Matt Walker tiny cookstove build in Portugal

as the sealing off of the cooktop has improved the stove s flue pull/draw, looking at the left side of the cooktop , it has several ring inserts ,could those be drawing in too much air , if you could seal them up with clay slip at first to experiment further , or a large steel plate over it sealed with clay .

In light of the graphic about the chimney positions outside the house, I had a look at what we have so far and there's a good 1.5m of flue above where it comes through the roof, and since the roof slope is under 45°, that means there's more than 1.5m horizontal clearance from the top of the pipe to the roof, because geometry.  There's an option to get half-metre lengths of pipe (or even 25cm) but I'm gonna hang fire on that for now, as I've a feeling the chimney is good.  

As for the rings on the stove top, I've not seen any smoke sneaking out around them, so although they're not sealed per se I doubt there's much of a leak there either.  At some point I might smooth off the metal a bit as they're basically just as-cast, and they'd probably sit nicer for being smoothed out but I don't regard that as a priority.  The gap between the plate and the surround bricks was much more obvious.

tony uljee wrote:as the sealing off of the cooktop has improved the stove s flue pull/draw...

The thing is we're not 100% sure if it was the sealing off of the cooktop that has caused the improvement or the fact that the bricks are gradually drying out.

I think what we should do now is to leave things pretty much exactly as they are for a week or two (depending on how often we light it...) while it continues to dry, then when improvement stops happening we can tweak other things.

We had two half-burns yesterday evening, which is around an hour of active burning in total. This made the place lovely and cozy on a very wet day. And there was still warmth coming off it this morning. And there isn't even a bench there yet...

Time for an update.  I keep burning it once most days and it shows signs of behaving better but I still needed to address the smoke sneaking out of the door.  This was always intended to have a fire proof rope seal between the door and the firebox.  When building the core, I left what I fondly imagined was a suitable recess between the front face of the stove body and the front of the core bricks, where I intended the rope seal to sit.  The plan was to make a groove for the rope inside the door, using some 6mm square section steel rod.  Well, it still is, kinda.  Having assessed it and also in light that the fattest rope I can readily get is only 8mm (I had in mind 10mm), there was no way the rope was gonna fill the gap.  

I first welded a frame of 25mmx3mm flat steel inside the door to match the shape of the front of the core.  Then I welded the 6mm bars to make the groove as planned onto that.  All of this helps to stiffen the door which is only made from 3mm plate so not really as stiff as it might be.  Then I put a decent amount of high temperature fire cement stuff (1200°C rated) which mostly filled the new groove and pressed the available not long enough bit of rope around the top of the door and most of the way down the sides.  However, the rope still didn't meet the face of the core.  So I cut some more bits of the 25x3 steel and stuck them around the firebox opening with high temp silicon.  That gave the rope a nice surface to land on and lo! it did indeed contact.  After lighting and burning the stove, the emission of smoke from the front was almost entirely gone!  Yay!

So today I happened to be passing the hardware store and picked up another rope kit, pulled off yesterday's rope and put on a new one which went all the way around, leaving the existing cement and adding a thin new layer to stick the new rope:

Then I shut the door to hold it in place.  The cement will dry a bit on its own and will cure nice and hard later when the stove is lit this evening.
Here's a pic showing the landing face around the firebox opening.  I kinda like that, makes it look sort-of official.  I hope they stay on there.


Will see how the new rope fares.  There was a teeny amount of smoke still sneaking out, but maybe I pulled the first rope a bit long:  it's kinda stretchy and you can vary the effective diameter of the rope a little by how much you stretch it when fitting it.  This new one I didn't stretch so it makes a nice fat seal.

Theres a ceramic fibre packing /rope sold by vitcas , its available in 30x30mm square cross section and in 40x20mm rectangle cross section, they also have the usual rope type cross section in sizes from 20mm to 50mm in cross section ---the 40x20 its what i had planned to use but for being impatient to get moving on and having the ceramic fibre board to hand is the way i landed up going with.

It looks like you are sorted well now, but I was going to suggest vitcas too. They do sell direct and were very quick in sending up my bits for refurbishing our range cooker which needs a new firebox lining. I had to restrain myself....

Nancy Reading wrote:It looks like you are sorted well now...

Well we still have the bench to build, but even without the bench this is by far the best wood stove I've ever had. It's still a bit fiddly to light, but it gets better each time we burn it, which isn't every day yet but as the weather cools it's getting more frequent. The house heats up more gently and stays warmer longer into the night. Plus it's using significantly less wood. I tried to get a figure out of Himself but all he was willing to share was "Next to f*** all compared to what we usually do. We'll know better by later in the year."  I'll work on a more printable, and accurate, estimate by spring...

Rosa snuck off with Austin last week, inspired by an old painting she saw of raising a baby dragon which involved feeding it and puffing breath into it with a pair of bellows. And she came back with this, which is helping with the lighting. At least, once Austin had learned to huff it slowly and gently instead of blasting it with full force...



Austin has named it Lobinho,  which means little wolf, on the grounds that it huffs and it puffs but, hopefully, won't be powerful enough to blow the house down. Especially as it's made of bricks.  

I do worry sometimes that maybe I'm a bit of a bad influence on him...

Meanwhile, my dragons inform me that the new dragon who now inhabits the rocket mass heater is called Cuca. Usually in Portugal they call her Coca, but my dragons insist that she prefers Cuca. But then, I suspect my dragons just like arguing over which vowels to use. They do the same incessantly with the giant sea dragon, who is either called MOR or MAR depending on which dragon you ask. She's an enormous dragon who lives along the middle of the sea floor, snoozing gently but gradually spreading her massive wings under the continents and wrinkling them up along the edges a little. Or something.  Serra, who is Portuguese, insists that her name is MAR, while Rubeus, who is Welsh, insists it should be MOR. They both mean sea so I think it's just excuse for them to squabble.

Anyway, Cuca is settling in well and finding her voice. She tends to hang out in the forest at night but has found that the children she used to help find their way home if they got lost have all grown up and forgotten her, and most of the children these days are frightened of her and blame her for all sorts of things. And every year someone called Jorge hunts her down and attempt to cut her ears off. So she needs somewhere safe to hide while they grow back.

but I was going to suggest vitcas too. They do sell direct and were very quick in sending up my bits for refurbishing our range cooker which needs a new firebox lining. I had to restrain myself....

Thanks for that link - very handy for anyone this side of the pond  (mor? mar?) to source things.

Pity they don't sell ceramic glass for door windows.  However I did find a website in Spain that offers that cut to custom sizes.  While I intend putting in a window, it's not a priority so I can keep looking for a local supplier.  The problem is that most suppliers supply specific cuts for a known brand of stove, so finding the size you want can be tedious.

Austin, is there a large outlet that sells stoves in your area, if so they will probably  replace  stove doors with cracked or crazed glass.
I visit my local  store every few weeks to see if they have any off cuts or any second hand cracked glass.
In fact at this time of year they have a bin full of old glass, sometimes I can get really large pieces and there are always a few band new off cuts to take away.

could try portugal s ebay , look for high temp glass ,neoceram , or robox  not sure though if you are under the same import taxation for import of goods outside the eu, as we are in ireland . so look for stuff coming from germany ,italy  some suppliers are damn expensive and postage is unreal ---so shop around ---i spotted some from italy with only a couple of euros postage---ifs its from usa dont bother as the postage will be more than the glass is and you could face a customs charge /tax on top of it.

I found 2 old wood stoves in the dump that I scavenged the glass doors from that I plan on using for a future build.

Here goes with today's update :)

Stove a bit grumpy to start but to be fair
a) I put the fire together the other way up, because it appears that others running batch boxes do that - viz. with the kindling at the top.  I don't believe that was the grumpy start issue.
b) I didn't bother to prime the chimney, partly to see if it would start without.  It's also still marginal on temperature, I don't have an outside thermometer to hand but I'd be surprised if it's much under 15°C/60°F out there.

I'm still debating primary air inlet, after looking at this thread in which the topic cropped up.  I imagine an inadequate primary air intake is gonna make it burn slower and start harder.  That said I don't really want to go OTT on it either.

We're around 560m/1860ft altitude here, so not crazy high but a fair way from sea level.  Currently the primary air intake is 30 x 12mm holes, which I like the look of but only adds up to about 5.25 sq in total.  From reading that thread I think I may need more.  Added to the total area, it's probable that 30 x 12mm holes don't actually flow the same amount of air as a single 5.25" hole would.  There's space on the door to drill more holes, or I could buy a bigger drill and enlarge the ones I have, or both.

For others who have a 6" batch, Matt Walker or otherwise, how big did you make your primary air intake?

Austin Shackles wrote:For others who have a 6" batch, Matt Walker or otherwise, how big did you make your primary air intake?

I have a 6" now-standard batchrocket mass heater here. Its air system is a combined air inlet, feeding both primary and secondary air. During the course of the burn the emphasys shifts to secondary, this is intentionally. This single air inlet is 3x14,8 cm, horizontal opening, 44.4 cm² or 6.88 sq. in. The total area of these holes is 5.25 sq in, might be too small as compared to my single air inlet.

Also, a lot of smaller holes together has more circumference than a single larger hole. As a consequence, more friction is created this way. Which in turn means you'll get less air inside. My opinion: you'd do better to switch to a single larger opening.

As an aside, I start my heater with the door open a generous crack to allow enough air in. Combustion air is a volume, the product of opening and air velocity. The stronger the pull of the chimney, the more air is coming in through the same opening.

So far we've been lighting the rocket mass heater around three times a week, depending on the weather. This has kept the house at around 20ºC (68ºF), which is where we like it. If it drops below that, we decide it's time to light it up.

I also decided to do a little experiment, which won't be completed until Christmas. We went out for a walk and I found a stick that we guestimated to be around the right size for a burn. It was the right size for me to drag home without undue exertion, so home it came!



Then we took another photo that actually showed how big it is, with Rock for scale, as usual...



The wood itself was dry as it has been down for a year or so, but the surface was damp as it had been raining recently so I put it somewhere it could dry out for a bit. Then today we sawed it up to size and put it on one side and declared it to be some kind of Yule log, ready to burned at or around the solstice.

Here is Austin attempting to get it into sensible sized and shaped pieces to fit into the firebox.

There are lots of offshoots and twiggy bits and bits of bark, which actually makes a good mix as it has built-in kindling.



An olive crate makes a useful container for it so it doesn't get mixed up with the rest of the wood.



There.

We got that much out of it.

Might even weigh it some time.

Not a huge amount, but it was a very achievable amount for me to drag home while out walking.

It will be interesting to see if it really is a day's heat in December though.

Time will tell...



And then I noticed this...



There's a preying mantis ootheca in the olive crate!  

It's probably not viable now, or already hatched, but I was reminded of one of my very few house rules with my late husband - "no coming to bed with oothecas in your pocket". I shall leave it to your imaginations why I instigated that rule....

Great demonstration of how the stove is capable of using timber as found and the efficiency of that , no timber is wasted or considered not suitable anymore  , i am thinking now of how bundles of stuff used to be collected , trimmed and tied into faggots whilest held in a special steel frame work made for this process---i could make them firebox size and a blend of smaller on top bigger on the base---put into the firebox and a fire lighter---homemade of course---and just let it go and roar away.

I just weighed the wood in the olive crate - 2.8 kg, or 6 lb 4 oz.

And speaking of faggots, did you see my post in the carrying things on your head thread.  I refrained from using the word 'faggot' there as it tends to get misunderstood. Even I tend to think of them as something that is served with chips and mushy peas...

yes the word has been hy jacked and distorted , i suppose it could be be brought back into our domain and use by using the older spellings of it and remembering its importance to us --- rather than it s misused meaning --part of our older culture and traditional use of it-- is coming up to that  time of year  to burn it for household goodluck ---as you are intending---so heres to your goodluck ---cheers

Time for another update on running the stove... I have some points in no particular order and as usual welcome any comments:

* Others describe stacking wood in the box with kindling on top.  I tried this but I'm ambivalent about the results.  One thing I've noticed is related to some of the wood I'm using which is old roof laths, so rectangular sawn about 1" x 1½", and I note that I need to be a bit careful about stacking that to allow some air space around it, or it tends to stifle the draft.  Anyway, I seem to get the best results by starting a little fire at the back of the box with some ripped up egg carton and small sticks, then when that's burning stack the fuel on it.

* Primary draft.  I previously enlarged the holes in my door to 12mm.  There were 30 holes and that worked out to about 5.25 sq in in total but I had a feeling that 30 small holes didn't flow as much air as one single 5.25 sq in opening would, 'cos fluid dynamics is complicated.  The other day she was a bit grumpy about lighting and I noted a distinct improvement with the door open.  So I drilled 7 more 12mm holes in the door (it fitted the pattern that was already there) and that increased the total area to almost 6.5 sq in.  The result shows significant improvement in burning compared to what it was.  I think I probably have the primary draft good now, gonna run it for a bit and see.

* Burning with/without bypass.  I'm confident the chimney draws fine: if I put a small fire at the base† of the chimney it draws and burns nicely (this is used to prime the chimney if needed).  The main fire burns well with the bypass open, but shutting the bypass completely seems to slow it down more than I expected, and can lead to smoke sneaking out in odd places.  I feel it's not burning fast enough to burn as clean as it should, with the bypass shut.  I can get it to burn quite well with just a little bit of bypass.   It's just occurred to me though that because I have yet to build the bench which is planned to go alongside it, I have the 2 bench openings at the bottom of the stove and although I stacked some bricks against them to shut them off, they aren't sealed as such.  Maybe this is the problem and I should temporarily seal those openings better until I can build the bench?  There's also the point of the lower oven door.  That fits fairly nicely against the brick shell but it isn't specifically sealed around the edge.  I've noted that opening that door makes a big difference when the fire's burning so maybe I need to think about a better seal there too.

† It occurs to me now that it would be possible for the more adventurous builder to incorporate a small door down there for that purpose.  However I have a small steel shovel with an extra long handle and can slide that in through the bottom oven door to position it, which also leaves any residue from the priming material on the shovel and thus easily removed.  Of note is that it's best to leave the oven door open while priming.

It might help if you could post a video of the stove working as it is very difficult to accurately comment from afar but it sounds like you need more draw.
All riserless cores rely of a strong draw to work efficiently, a tall insulated chimney with a straight run is often required to get the best results.
This becomes even more important when the stove is forced into down drafting benches etc
How much smoke is coming out of your chimney on start up and how long is it visible for?

Austin Shackles wrote:It's just occurred to me though that because I have yet to build the bench which is planned to go alongside it, I have the 2 bench openings at the bottom of the stove and although I stacked some bricks against them to shut them off, they aren't sealed as such.  Maybe this is the problem and I should temporarily seal those openings better until I can build the bench?  There's also the point of the lower oven door.  

Update (again? whoa there tiger)

OK so this morning I made up some clay mortar and sealed around the bricks that are obstructing the going-to-be-bench-flues-one-day, and for good measure put a bead of silicone around the inside edge of the lower door.  Then I waited most of the day until the silicon wasn't sticky.

It's not that cold today (just over 18°C/65°F inside), so ordinarily would barely need a fire.  But I went ahead and lit it anyhow, to see how it was behaving.  I'm cautiously optimistic: I didn't prime the flue as I was keen to see how it coped without.  Took a little fanning to persuade the smoke to go up the chimney but once it caught alight properly it drew nicely with the bypass open.  Having gotten it going and loaded it with a modest amount of fuel, I started closing down the bypass.  Got to full shut and it burned quite well for about a half a minute and then quite clearly stalled: smoke started to emerge merrily.  Cracking open the bypass maybe half an inch started it up again.  I let it burn like that a bit more, so that the body of the stove could start to warm up, and after 5 or 10 minutes the oven door was 29°C/84°F vs the brickwork of the lower body still at about 18°.  That door is a single sheet of 3mm steel with no insulation.  

Then I shut the bypass again and this time, so far (fingers crossed) it kept burning.  Makes sense to me that you need a minimum temperature* at the base of the chimney to make it draw and that, with the whole stove cold, shutting the bypass too much/too soon causes the exhaust gas temperature to go below that minimum.  If you put your hand on the chimney where it's single skin emerging from the stove, it gets quite hot with the bypass open.  Partly-shutting the bypass almost immediately cools that chimney base temperature.

So I'm a calling today's experiment a success pending more experiments later.  No doubt the weather will oblige in being colder before long and then I can see how it behaves then.

As for the flue:  the initial maybe 12" emerging from the stove top is single skin.  It bends 45°, changes to insulated, goes through the wall and has another 45° outside then goes up the side of the house and currently terminates comfortably beyond the 1.5m distance  from the roof that was shown in that chimney/roof graphic posted earlier in this thread.  It wouldn't be hard to extend it a bit more, but to make it a lot taller would need to devise some additional support, I think.  I'd need to check with the makers of the pipes.  I'd be OK with adding another half-meter to it as is, but I don't want to do that (it's not cheap) unless it really needs it.

* depending on the conditions at the time.

Today's News from the front

About a week ago I decided that I was running out of things to mess with and tweak on the stove and yet it still didn't really burn with the ferocity I'd kind of hoped it would.  So I went to the chimney factory and bought another meter length of 150mm double wall insulated flue.  [if it's of use  to anyone, it's called Eco-Ar and is on the Zona Industrial in Fundão, Portugal.  Not just a sales place, they actually make the flues there.  1m of insulated 150mm is €75 including tax and including the clamp ring that attaches it to the one below it.  They seem well made and have nice little touches like the screws for the clamp are captive so they can't be lost]

After some delay arranging a day when both Alan and I were available and it was decent weather, compounded by needing to make a thing with a couple of stays to support it, this got fitted yesterday so now not only is the flue exit compliant with that diagram* someone had further up the thread, but it also reaches just above ridge height on the roof.

Yesterday's burn went pretty well.  With the bypass open it lit readily and drew strongly, and I was also able to shut the bypass sooner without it stalling.  Previously, shutting the bypass too soon it would continue to burn for a few minutes and then quite suddenly would stop and make clouds of smoke.  It was also not all that cold outside.  There will be more tests in the coming days.

I've also been messin' with the laser-guided temperature-teller (an essential tool ) and concluded that the hotplate above the core exit gets up to water-boiling point pretty fast.  Shutting the bypass most of the way diverts most of the exhaust around the "long way" inside the stove, which of course extracts heat from it as intended.  I find leaving the bypass open a bit at this point keeps the chimney base (at the top of the stove) warm enough to ensure good draft. Once the (non-insulated) door of the lower oven space reaches 25-30°C (77-86°F) the bypass can then be fully shut.   As an interesting side-note, before lighting, the whole stove is about ambient temperature, let's say for example 18°C/68°F.  As soon as I divert the exhaust around the stove and start to warm the body of the stove up (and, later this will include a bench), the oven door quite soon starts to get warm but the lower part of the brick body actually cools by a couple degrees.  Later of course it begins to warm up above ambient.

Lastly if anyone's still reading I've been having thoughts about the size of the fuel.  This stove has a firebox about 6½" x 6½", and it feels to me that trying to put in single pieces of wood bigger than about 2" is counter-productive.  Clearly I could put a straight log about 5½" diameter in it but I doubt it would burn right if I did, so....

Question for people running batch-box style rocket things, what size is your favored fuel vs the size of the firebox?

* I've a feeling the diagram showing good flue exit points is for a regular wood stove, so it might be that a rocket stove needs a more generous allowance.

Sounds like you are getting to know your stove, you just need some cold wind to test it out with, then you might see a more impressive burn.
I have never built a Matt Walker stove so I dont really know what to expect but, cold weather should see increased draw and therefore higher stove temperatures.
The fire box on my 4” vortex stove is 8x8x13” but I keep the fuel 3” back from the door glass, hottest burn come from loading random thickness pieces of around 1-1.5” square with kindling size pieces for the top 10%.stacked with a 2” gap on top and of course top lit.
Longer burns are loaded differently, with kindling at the top and getting bigger as the stack goes down, the bottom would be much larger pieces.. ie .. 10” long 3x2”.
For a long uninterrupted burn, using the bigger prices at the bottom, I will fill to the top just leaving a one inch clearance on top, that will last about 1.3/4 hours to get to coals.
However you will probably find your own preferences that suit your circumstances.    
Interestingly my vortex J tube is not remotely fussy about fuel and gobbles up anything from sticks to 3” logs in any order  without any issues but it runs with a 30” tall insulated rise and a straight up 4 meter chimney.

Hi Austin;
Adding the newest section of chimney pipe and having it reach above the ridgeline will work well for you.

For wood size.
I have three Peter Berg design batches, the fireboxes are much larger.
My 6" stoves can burn large 1/2 rounds or full 6" logs easily, with room for cookstove-size pieces around it.
In my 7" batch I can stack three or four 6" rounds with quite a bit of room for smaller wood around them.

The fireboxes on all the Walker-style riserless cores are much smaller.

I have Matt's BBQ oven (I call it a black-and-white oven).
It uses the same size core as the tiny cookstove.
My wood for it is split down to triangles with 1.5"-2.5" (38mm-63mm) per side.
Having grown up using traditional wood cookstoves I  think of this as standard wood cookstove size.
Because I am running an oven to cook outdoors, once it is warmed up I can easily burn 5.5" (139mm) rounds with a couple of 38mm pieces around it.

My Walker is built with heavy firebricks, it is hard to start even with the white oven open (bypass-sort of).
When starting it cold, I use short kindling directly in front of the secondary riser, once the bricks heat around the 180-degree bend and the draw starts going, I can start adding cookstove-size pieces.
Once the core is fully warmed up (Screaming Hot) I can burn any size that will fit inside on top of the coals.

I've tried top lighting but I get on better with a small kindling fire at the back of the box by the secondary air, as you mentioned.  Once that's burning nicely I can stack full length wood on it.  

The climate here is such that burning for an hour or 90 minutes will give enough heat most days.  Sometimes it's colder and I expect to burn it a bit longer then.  I shall split down the bigger stuff and reserve larger bits for restarts after the first burn, I had already concluded that it burns better once the firebox is nice and hot.

I made a nifty device for pulling any ash out of the firebox, and that doubles handily as a way to push the hot coals to the back when adding more fuel for another burn.  I'll take a picture of it sometime.

It's the end of November now and we're currently burning pretty much every day, sometimes just one burn, sometimes reloading once.

Here are my thoughts on its performance so far.

1. It uses a small fraction of the wood we'd usually use, and the house is a much more consistent temperature than it ever was before.

2. The mass in just the brick cookstove is probably adequate for a house this size in this climate, though my view on that might change over the next couple of months. I still want the heated bench though - I've wanted one too long!

3. It gets easier to light, especially as the outside temperatures drop, tweaks have been happening to the build, and we're getting used to lighting it. I'm glad we went slowly and learned how each tweak affected things. Austin is the one who usually lights it, which gives him a chance to notice changes day to day. But if he's out working and it's a cold evening I'm quite happy to light it so it's one less job for him to do.

4. Burning twice instead of only once makes a bit of difference to the house temperature at the time, and a lot of difference to how long the heat keeps coming out and how cozy things feel the next morning.

5. The stove top gets hot! We're not actually using it for cooking at the moment because the whole kitchen is set up upstairs and it's a bit too much of a faff to carry stuff up and down stairs, but the cooktop gets wonderfully hot. Austin tests it with the temperature gun, I use more, er, traditional methods...

6. For this climate, at this time of year, the oven is NOT a practical consideration for actually cooking anything. We simply don't run the stove long enough for the oven to get up to temperature as any surplus heat gets shoved into the mass of the bricks before it reaches the oven. If we burned long enough I'm sure it would work fine, but I suspect when we finally move the kitchen downstairs I'll be using the stovetop to start things off and then a haybox for finishing off anything that needs long, slow cooking.

Burra Maluca wrote: 6. For this climate, at this time of year, the oven is NOT a practical consideration for actually cooking anything. We simply don't run the stove long enough for the oven to get up to temperature as any surplus heat gets shoved into the mass of the bricks before it reaches the oven. If we burned long enough I'm sure it would work fine, but I suspect when we finally move the kitchen downstairs I'll be using the stovetop to start things off and then a haybox for finishing off anything that needs long, slow cooking.

As a bread baker, I have to ask...
Could you actually move coals from the batch box to the oven section to get it up to temperature, sort of the way a traditional cob oven is fired?

We make a no-knead bread in a glazed cast-iron casserole which we pre-heat at 425F for 30 minutes, put the dough into in and the lid on, and bake if for 30-35 min. Then we remove the lid and lower the temperature for the final 5-10 minutes. Great stuff and pretty easy to make. It also warms up the house in the morning, but sometimes the house is so cold overnight, I have to put my heated rice pack under it in the evening to give the yeast a fighting chance to get their job done!

Austin Shackles wrote:

† It occurs to me now that it would be possible for the more adventurous builder to incorporate a small door down there for that purpose.  However I have a small steel shovel with an extra long handle and can slide that in through the bottom oven door to position it, which also leaves any residue from the priming material on the shovel and thus easily removed.  Of note is that it's best to leave the oven door open while priming.

Pre-heating ("priming") the stack to initiate draw seems to be common practice when firing the Russian style masonry heaters from cold.  For example, the first couple of minutes of this video, especially just after the 2 minute mark:

In this case, he has a hinged door for the purpose, but I have also seen a cleanout plug (with metal frame in the opening to allow easy removal and replacement) similarly used.

Not a rocket stove, and most certainly not a Walker Stoves design, but a similar problem to what you have faced.  In your case, not very much temperature difference between interior and exterior leads to low draft until the stack is heated, even at put-on-a-sweater temperatures.  In his case, there is also not much temperature difference between inside and out, but it's honestly cold, and it takes a lot of energy to get the stack warmed up.  Even though I think the batch box designs are most appropriate for people who have been accustomed to using conventional wood stoves (less retraining of the user), I am fascinated by some of these old Russian heaters and heater/cook stove combos.

Different from what he shows here, but it was pretty common in the Russian stoves to have a door like this, with the "vyushka" (draft blocker) inside, right at the bottom of the stack, but above the mass of the masonry heater.  The vyushka is a sort of double pot lid affair, which can be inserted to prevent standby losses up the stack after the burn tails out.  I don't think you can buy them anywhere in the West - maybe Ukraine or Estonia or somewhere, but I haven't seen them in the catalogs of any of the usual suspects.  Sliding blast gates - whether single or double - seem to be the commonly available hardware to accomplish the same (or at least similar) purpose.  The priming fire would simply be kindled on top of the vyushka, with the access door open (which then provided the combustion air to the priming fire).  Once the priming fire had burned out, the vyushka plates would be removed, the access door closed, and the fire built in the main firebox, with all bypasses open, to assure the straightest path for the new fire, with the least draft restriction.  Once the fire was well established, the internal bypasses could be manipulated to begin heating the cooktop plate, warming the bake oven, etc.

Your approach seems to work well, and doesn't leave a deposit of ash in the stove, so it seems ideal to me - less hardware to purchase, fewer penetrations to build and maintain.  Perfect!

I have been lurking, following your build and Tony's of the Walker stoves.  Thanks for sharing your progress/process.

Now the weather is cooler it's starting easier (and I did also extend the chimney another meter).  I did prime it the other day as it was starting from stone cold.  However last night I didn't do that and it also started pretty easily.

This leads me to my Thought of the Day (yesterday).  When it's not that cold weather, I feel it's maybe going to be better to burn the stove for longer every other day, rather than a shorter burn every day.  The initial burn has some inevitable loss of heat while starting, whereas a re-start once it's burned down to some nice red coals doesn't need any bypass or anything to heat the flue, so you get to harvest all the heat from that second batch.

I imagine when it's colder I will want to burn 2 batches a day to get enough heat.  But for now, it's still like 18°C / 65°F outside on a nice day.  One batch gets the stove quite nice and warm, but 2 batches sequentially puts significantly more heat into the brickwork.

Jay - I'll come back and talk about ovens and things when I have a bit more energy. For now I want to share some photos of Cuca in action.

Vermelha, my fiery young dragon, wanted to demonstrate how to wake Cuca up using her favourite snack - a dry corn stalk harvested from the GAMCOD bed, and a giant pine cone.



She shoved them right in the back of the firebox, near the secondary air feed.



Then she huffed on them for a few seconds.

I guess if you don't have a resident fire-dragon then you may have to improvise with matches or something, but Vermelha is very useful for this job.

So long as you remember to open the bypass, the flames immediately begin to draw to the right, around the corner, where they meet the magic portal and are mixed with the secondary air and the unburned gases to generate a re-burn.



When Cuca ws purring like an overgrown pussycat, which didn't take long, I shoved as many bits of wood as I could into the main fire-box so that the fire would spread from the appetiser to the main course.

A lot of our wood is offcuts from building jobs. I make sure that it's stacked so that there is plenty of air between the bits of wood else it might not get going properly, especially in this first batch.

The firebox in this rocket mass heater is small. With a bigger firebox it might be possible to induce an overburn if you load it up with too many small sticks with too much air, but it's really not likely with this set up.



Cuca has woken up and is purring like a giant pussycat.

Now I have to gradually shut the bypass down so more heat is diverted around the rest of the system instead of escaping up the chimney.

When the lower oven door is around 27C, it seems to be safe to shut the bypass completely.



40 minutes later...



After another 25 minutes, ie just over an hour after ignition, this had burned down to mostly just hot coals. So I gave her another batch of wood.

She's a good dragon and deserves dessert after all!

I shoved a few more sticks on her while I played with the laser thermometer.



Chimney reading isn't easy to take as it's shiny metal. It's likely higher than this. 29C is around 85F.

Most of the chimney is insulated, but the bendy bit that comes out of the stove is uninsulated and will give a good idea of the temperature of the gases escaping up the chimney.



It feels pleasantly warm to the touch, but I could happily leave my hand there so it's not wasting too much heat.



The hottest part of the hot-plate however is 196C!

For any of who want that in archaic, that's 384F.

The hot gases snake their way around under the cast iron hot plate. Further back it's not quite so scorching hot, and over on the far side it's cooler again. This is where the initial burst of heat to warm the house comes from.

The rest of the heat is used to warm the bricks, leaving enough heat to create sufficient draught up the chimney. The hot bricks will keep the house at a nice temperature overnight when the stove is out.

But there is plenty of fast-heat too!



Aha - Cuca has got her teeth into those sticks in the time it took for me to take a couple of temperature readings. She's such a good dragon...

good result, and maybe a first on the forum --a stove built from scratch and worked at to get it going ,improvements made and shown ---and now how its running and performing ----congratulations -----i myself am still working away at mine ---the flue is becoming a major engineering project in its self

Another quick update because we've finally had a couple of weeks of weather cold enough (we hit freezing!) to assess performance when the heat is really needed.

Bear in mind that

a) we haven't built the heated bench yet
and
b) the house is crazy draughty, which might or might not get fixed over the next year...

During less cold weather, one burn with maybe one re-fill most days was plenty to keep the temperature where we like it.

When the temperature dropped down to near freezing though, especially if there was wind, we'd need to re-fill several times. We found out that there was only so much heat that the bricks in the stove itself would absorb. After that the chimney  temperature rose and we were losing heat. We need to get that heated bench built before next year. We both feel, however, that in less cold weather, when the draught isn't so good, having the bench might make it difficult to light. So when we do build it we want to put a close-off in place so we can isolate it. At the moment it is being a total dream to light but we have memories of the very start of the season when it wasn't so easy and want to make sure. And anyway, with the option of closing it off we can make comparisons. It might be perfectly ok now that the brickwork is dry and the chimney is taller. Or it might be that in this climate shutting it off is a good thing that we should recommend to people if they build one the same.  But it seems that after two or maybe three loads of wood, more heat is going up the chimney than I'd like. For now we think that maybe a short burn in the morning and another in the evening might mean less wasted heat.

tony uljee wrote:good result, and maybe a first on the forum --a stove built from scratch and worked at to get it going ,improvements made and shown ---and now how its running and performing ----congratulations -----i myself am still working away at mine ---the flue is becoming a major engineering project in its self

Your build is looking awesome Tony! Please keeping sharing all your updates.

I had a possibly crazy thought - if you aren't using the oven right now, could you put slabs of marble with gaps for air flow in the oven section to add a little extra thermal mass until you are ready to build the bench? I'm not sure what the cubage is in the oven, so how much difference it would make?

Jay Angler wrote:if you aren't using the oven right now, could you put slabs of marble with gaps for air flow in the oven section to add a little extra thermal mass until you are ready to build the bench?

The only problem with that idea is that the cold spell has stopped.  It's currently 18C (65F) outside, expected to fall to around 5C (41F) tonight. So we are unlikely to be burning long enough for the extra mass to make a difference. The experiment I will probably try next time we have a cold spell is to light twice a day. When we've figured what difference that makes, if we get another cold snap we might try with extra mass in the oven.  

Jay Angler wrote:

Burra Maluca wrote: For this climate, at this time of year, the oven is NOT a practical consideration for actually cooking anything. We simply don't run the stove long enough for the oven to get up to temperature as any surplus heat gets shoved into the mass of the bricks before it reaches the oven. If we burned long enough I'm sure it would work fine, but I suspect when we finally move the kitchen downstairs I'll be using the stovetop to start things off and then a haybox for finishing off anything that needs long, slow cooking.

As a bread baker, I have to ask...
Could you actually move coals from the batch box to the oven section to get it up to temperature, sort of the way a traditional cob oven is fired?

I'm not actually much of a baker, but there are a few possibilities. I'm sure I saw somewhere that you could use the firebox itself when it was nearly out. Just push the glowing coals to the back and use the residual heat in the front of the firebox. It's a pretty small firebox but I suspect it might work well. I think this would be a safer way to do things than actually moving coals around. For me anyway. I get a bit wobbly sometimes...

Matt Walker made an attachment for his stove to cook on top of part of the hot-plate.  



It doesn't actually appeal to me - I love the look of the cookstove as it is without an extra box stuck on top.

I'm going to send off for a thermometer to put in the oven door to monitor the temperatures in there, which might give us some good information.

We seem to have been a bit quiet on this thread, mainly because until we're ready to build the bench, the build is basically complete.

The stove is running well now, having dried out and the outside temperature being a bit lower, and the taller chimney and all that.  I still use the bypass to start it, but on a good day it would start without but would take longer to get going.  By making the initial starting fire with full bypass it gets roaring nice and fast, can then load it up, shut the bypass down to about a quarter, then wait a bit until the oven door gets to about 27°C, at which point shut the bypass and let it get on with it.

The initial burn loses a bit of heat up the spout as a result but the ease of lighting and absence of smoke means I think that's acceptable.  

Re-starts are generally without hassle unless we do a Paul* and rarely need anything beyond using the special tool to shove the embers to the back of the box by the secondary air tube.   Unlike the J tubes that Paul mostly favours, we find a burn runs approximately an hour from filling the box until it being ready to re-start.  I suspect maybe if we used really small sticks it'd be faster and we'd get faster heat but a 1 hour stoking cycle compares well with the conventional wood stove: the difference being that we run this for at most 3 hours, whereas in winter the woodstove had to be run flat out for 6-8 hours to get the house warm on a cold† day , using more wood and more effort.

It's now quite well established that more than 3 consecutive burns without a bench or other additional heat storage starts to get wasteful as the majority of the stove is by then nice and warm and you start sending warmer-than-optimal gases up the chimney.   To solve this until we DO have the bench, we burn it a couple of times a bit earlier, then leave it a few hours and re-light it later once some of the heat has gotten into the house.

On the topic of the clay mortar, there have been issues with the top layer of bricks coming loose.  It might be I needed different sand: the sand I used is what is sold here as "yellow" sand and would ordinarily be used with cement or lime for rendering, not bricklaying.  It just doesn't bond that well to the bricks and yes, I know that makes it easy to take it apart, but I don't want on-going maintenance requirements sticking it back together, either.

* in the Xmas podcast about RMHs, Paul mentions that he gets distracted and returns to feed the beast only to find that there're just a few small embers left, not enough to start the next batch of sticks burning.

† where cold mostly means in the 0-10°C range (32-50°F) .  Not COLD like in, say, Montana

One of the main noticeable differences in my life since having the rocket mass heater is that I no longer use a heated blanket on my bed during the winter. I'm usually totally addicted to it, but now the temperature is much more even and I haven't felt the need for it all.

The only exceptions have been due to some weird health thing I have going on where I go hypothermic if I over-exert myself. I've managed to do this four times this winter and I've used a small heat pad (and big steaming mugs of cocoa!) to sort myself out again. The only time we've cheated and put an electric heater on was one exceptionally cold day when we'd been out all day attempting to get some tests done to figure out what is actually wrong with me and we'd come home with me hypothermic and the house cold because we hadn't run the the rocket mass heater that morning.

It's also been notable that as winter has progressed, we've both gradually adapted to lower temperatures. At the start of winter we'd feel cold at 18C (64.5F). Right now it's 16C (61F) and we both feel warm and cozy. The same sort of thing happens in reverse during the summer and we gradually adapt to the heat. Which I find fascinating, especially as it seems so many people can't function unless their homes stay within very narrow ranges of temperature. I suspect our bodies are capable of adapting far more than we give them credit for.

We've also decided, for various reasons, that we're not going to follow through with tying up bundles of sticks to feed en masse into the firebox. At first we thought it would save time, but in actual practice it's really no problem to grab what we want from the piles of sticks. Plus sometimes there are still loads of hot coals which, when pushed to the back of the firebox, mean that the floor of the firebox is no longer level so we need a bit of creative stick-stacking. And at other times we've let the coals run down a bit, so we want smaller sticks so that they catch fire more easily.

But the main reason is actually dragons. In particular, baby dragons. They are breeding. Again. And the babies hang out on the piles of sticks. If we pick up sticks singly and bundle them together, the baby dragons jump off. But I'm scared that if there are ready-tied bundles of sticks they will just hide inside. And Portuguese house-dragons simply aren't fire-proof. So I've banned the tying up of bundles of sticks for fear of accidentally burning any.

I mean - just look at them!

And, um, speaking of baby dragons, exciting things may be happening, which has instigated some new developments in and around the rocket mass heater. Which may soon become an official hatchery...

A mystery parcel arrived yesterday, which has changed the trajectory of the projects here.

When we opened it, it looked like this...



Rosa was immediately drawn to that pretty tartan ribbon, as she'd been looking for a ribbon to experiment making ribbon roses and it seemed to fit the bill perfectly. So I opened that first.  Inside, rolled into some cardboard, was a mysterious message...

"Once upon a time in a land far far away, when dragons still flew freely over the earth, a Dragon Queen laid her eggs in the heart of a smouldering volcano.
For thousands of years the volcano kept the dragon's eggs at the perfect temperature. Then the earth cooled and grew old and solid and the eggs were locked, hidden in the rock....
...Until now."



Barely able to contain their excitement, the young dragons reached into the box and carefully removed the three cloth-wrapped treasures. Rosa carefully untied the strings, put the wraps on one side for making into zokin, and admired the contents.



Serra, who is rather experienced with such things, declared them to be the eggs of a Skye Dragon! She was not, however, entirely certain what the perfect temperature to incubate them should be, so Iggy, whose name is really Igneus and who has a natural affinity for both rocks and all-thing-related-to-heat, has gone off somewhere to do some research, leaving Rosa and Roxa to start designing a nursery for the magic Skye Dragon eggs.

They suspected the oven might be a good sort of place, so Rosa thought it was time to dig out that pretty cast iron decoration and fit it to the door. Roxa isn't convinced that this is the most important consideration in designing a nursery and is rolling her eyes impatiently.



Roxa believes that the most important thing to do next is to find out exactly how hot the oven gets, then when Iggy comes back with some figures for us we can work out where the eggs have to be. So while Austin was fiddling about decorating the door, she got him to install an oven thermometer. And then of course he had to light the rocket mass heater to see how hot it actually gets in the oven.

The girls settled down to watch the needle...



The heat from the burn mostly goes to the hotplate and to heat the bricks, especially for the first couple of burns. And, as we don't have the heated bench built yet, we tend to not burn more than three times as we end up losing too much heat up the chimney. So we suspected that the oven doesn't get very hot. It might get hotter next year when we burn it longer, but of course we won't know that until next year. By half way through the third burn, the needle on the thermometer looked like this...



Which I thinks mean smoking hot, but not hot enough to bake.

So now we have to wait for more information on how to hatch Skye Dragon eggs to decide how to proceed. I suspect that they should be kept warm but not too hot, then a quick burst of heat to help them break out of their shell. Which might mean making them a little home on or near the heated bench when it's made, then hatching them out individually in the oven when the time is right.

Watch this space.

And keep dreaming of how to make your dragons come to life!

Of course, after this time there is no knowing if the eggs are viable....Doing a bit of research - it is well known that dragon's eggs can be found in volcanos, and if the volcano starts to erupt that will trigger the eggs to hatch. Apparently the firebox of a steam train is the perfect temperature to finish the job then: (ref: Ivor the engine - Smoke Muntain). If the egg has not gone dormant, then it only takes an open fire to incubate the egg.

norweigian ridgeback egg in Hagrid's fire

source

(I'm so glad they got there safely!)

Well the weather here has been incredibly wet for days and days now. At some time last night, in the wee hours of the morning I heard a diesel cargo train screeching to a long, drawn out halt outside. Then a minute or two later the door clicked open and Iggy and Rubeus attempted to sneak back into the house, along with a rather old black umbrella which they'd been using to keep the worst of the rain off them. I knew Iggy had gone off to do some research, but I hadn't realised it was a father-and-son trip so I dried them off and asked them what they'd been up to and what they'd found out.

It's quite a tale!



Apparently they had flown back to the UK together to consult with a couple of old friends about the hatching of dragon eggs.

First they'd gone to Wales to consult Edwin Jones, better known as Jones the Steam of Ivor the Engine fame, about his experiences hatching dragon eggs in the firebox of steam trains.



Anyway, it turns out that Edwin Jones is an old friend of Austin's! He used to go down from Llaniog to visit the Teifi Valley Railway when Austin was a volunteer there and received his training as a fireman. I should have known I guess. Austin also used to volunteer at Internal Fire Museum of Power just a few miles away and he even took me to visit it when we were first together.

Edwin Jones explained that dragon eggs are like ideas. Sometimes you stumble on them unexpectedly, sometimes you go looking for them but never find them, and sometimes they are given to you by other people. Sometimes people have them but don't realise what they are or how valuable they might be. And sometimes people just have lumps of coal or rock and have overly grandiose beliefs about their value. But then, coal and rocks still have value, even if they aren't dragons and will never fly!

Having stumbled on an idea in the form of a dragon's egg, very often that egg will sit there forevermore and do nothing. But sometimes, almost as though fate is playing a hand, you will do something almost without thinking. Like popping it into the firebox just because it felt like the right thing to do at the time. And then the egg will hatch, and the idea will come to life, possibly even fly and sing. But the important thing if you stumble on any sort of idea is to do something with it. If nothing else, maybe share it in a place that other people can find it, then they can take it and put it in their own firebox and let the dragon fly for them.

Mr Jones then gave the dragons a nice cup of tea, showed Iggy how to make welsh cakes and then took them to visit Mrs Thomas' fish and chip shop as a special treat.

Then the dragons few off to Scotland to visit Hagrid!

Rubeus is an old friend of Hagrid's. Personally I suspect he's a very old friend of Hagrid's entire family but I can't quite put my finger on what makes me think that...

Anyway, Hagrid has devoted a lot of his time to searching out dragon eggs and hatching them and he's quite the expert at it. He says that whilst some people just happen to have the right training, the right job, and be in the right place at the right time to stumble on dragon eggs and have the right equipment to hand to hatch them, mostly it doesn't work like that. At least, not for him anyway. He has to work at it. And study hard. He says if he had to summarise what he's learned, it's that you have do something. Anything at all is likely better than nothing. And the main thing is provide the right sort of habitat for them. The proper container as it were. A bit like the philosophy of build it and they will come.

Any idea will take a bit of work, a bit of effort, of energy to bring it to life. And it's the same with dragon eggs. Edwin Jones' steam engine firebox was a perfect hatchery, but ideas will also hatch if you put them over a more gentle fire and interact with them. Interaction is important - befriend your dragons even before they become reality. He also pointed out our Cuca had moved in quite spontaneously when we built the rocket mass heater for her to live in. I guess we did build it, and she did come.

He also suggested that dragons are best hatched and raised singly, especially for novice dragon breeders. Give them as much time and attention as they need to develop well before moving on to the next one. Iggy explained our set up to him, and he suggested that for our Skye Dragon eggs, we should put them somewhere safe and cozy for now. Then finish off the heated bench, get the room down there all sorted out nicely, then when we are ready for our next project we can put one of the eggs to hatch. He said that maybe one of them is destined to be the dragon that lives in my son's rocket mass heater, so we can begin to think about designing that as we finish off the work on our own.

Iggy seemed very pleased with what he had learned and wanted to head back to Portugal to tell us all about it. Rubeus was a little concerned about him though, as Iggy isn't the best flyer and the weather was truly awful. Hagrid suggested that they take the train instead. That way they could do a bit of work on temperature readings in tunnels of various lengths and depths on the way home. Iggy thought that was a wonderful idea. Then Hagrid gave them a special present to help them in their quest, and also to keep them dry on the way home. A lovely old umbrella, built around a single rather gorgeous piece of wood with mystical carvings on the handle, which was made of the same piece of wood curved around somehow.



Hagrid said it was a very special umbrella with a safety tip over the end, just in case.



Just in case of what I'm not entirely sure, but anyway the dragons snuck on a few trains, headed back towards Portugal, took temperature readings along the way to see if the data would be useful some time, then hopped off that cargo train as it mysteriously stopped outside our house last night. None of my other dragons admit responsibility for anything, but did suggest that maybe it had been going too fast through the Gardunha tunnel and tripped the convel. Personally I have doubts about that, but something must have tripped it I guess...

All the other dragons were delighted to have the boys home again. Rosa ran off downstairs and rummaged in a heap of old kitchen stuff that we'd found in the house when we moved here, dug out a rather battered old enamel plate with flowers painted on it, declared it to be an appropriate container for the Skye Dragon eggs, made them a lovely warm cozy nest out of some raw (and smelly) black sheep wool, and laid the eggs on it.



Serra watched over proceedings with a mischievous glint in her eye, and I think the eggs are safe now while we gradually finish off the current dragony project and start preparing for the next one.

Who knows what magic and mischief and mayhem will happen then?

eva guo wrote:Wow. Looks great, Austin and Burra. Wish I could build one. I just stacked some fire bricks. Have no idea how to mortar.

EVA, this is a 2500 year old version of your version of a kitchen RMH cook stove!

See the attached photo. I scanned this off a very large display on Rocket Stoves on the Internet.

I just stumbled on a photo I took a year ago, when the new laser thermometer arrived, along with some temperature readings Iggy took when we fired up the old salamandra.

All temperatures in Celsius.

TOP OF STOVE
before lighting - 12.0
after lighting - 29.5
after few mins - 58
after a while more -140
30 mins later - 250

FIRST CHIMNEY BEND BEFORE EXITS WALL
start - 12.9
after lighting - 28
rising to - 50
after few mins - 98
after closing damper down a little - 103
after a while more - 140
30 mins later - 144

OUTSIDE BEND
after few mins - 90
after closing damper down a little - 82
after a while more - 110
30 mins later - 110

WHERE CHIMNEY GOES THROUGH ROOF
after closing damper down a little - 55
30 mins later - 55

THROUGH THE GLASS OF THE DOOR
30 mins later - 339



The bit that really struck home now that we've built the rocket mass heater is this...

FIRST CHIMNEY BEND BEFORE EXITS WALL
start - 12.9 C 55F
after lighting - 28 C 82F
rising to - 50 C 122F
after few mins - 98 C 208F
after closing damper down a little - 103 C 217F
after a while more - 140 C 284F
30 mins later - 144 C 291F

After just a few minutes, the first chimney bend before it exited the wall would be at 98C, or 208F. These days, if I stick my hand on the equivalent of that bit of chimney and it's much more than pleasantly warm, I refuse to feed the dragon any more wood as too much heat is going up out of the chimney instead of heating the room. And to reach that stage we've usually been burning for between two and three hours.