Austin Shackles

John Wolfram makes an excellent point.  I've been avoiding those kind of lights for precisely that reason. In my house though there's not one incandescent light.  For my work spaces I like a cool or daylight light and that's inefficient to do with incandescent, even with the modern ones with a halogen lamp inside: There used to be special "northlight" bulbs for artists with a blue glass envelope and you needed about twice the power rating to get the same amount of usable light.  

Other lights are a mix of cool or warm, depending on what was to hand and where they are fitted.  My partner prefers the warm one for a bedroom light. In the kitchen I have a 4000K 4ft fluorescent tube replacement which uses less power than the original 4ft tube did to give more light, it doesn't have a starter (it comes with a plug-in "starter replacement" which I guess simply connects the power to it) and has the added advantage of instant full power light just like the other LEDs.

Going back to Paul's original point about altering other, much more power-hungry aspects of your life such as using a washing line or clothes rack vs. using an electric dryer, or washing up by hand in a sink and putting the dishes on a drainer vs. using a dishwasher: I think the point is that swapping out the lights is a low-effort thing that most anyone can do at more or less zero inconvenience.  Making those other changes would have much more effect but many people don't do that because they don't want the extra effort.

There is one aspect of LED lighting where I can see a definitive benefit in electricity cost and that's traffic signals.  Some years back they began converting all the traffic signals in the UK to LED lamp units.  The old signals used a 250W incandescent bulb in each of the 3 lamps (I know because I asked a chap who was changing out a bad bulb once).  Consider a simple 4-way cross road.  In the UK that will have 3 signals facing each direction: one either side of the road at the stop line, and one on the opposite side of the road so you can see it when parked at the line.  That's a total of 12 signals on that one junction, and all of them have 1 light illuminated 24/7* for an ongoing consumption of 72KWh per day, or 26,280KWh per year for just ONE road junction. 26MWh of energy for ONE road junction!

Now consider the same junction with LEDs. Even if the LED lamps are 25W which I doubt, that would still cut the power consumption by 90%.

It's not the same everywhere as the lights differ: for example, I believe US rail signals use a mere 35CP bulb due to clever design of the lamp.

However I found this webpage about traffic signals in the city of Yakima.  They had 100W bulbs in their signals and their LED replacements are 15W, and the bottom line is that they cut the energy use per 100 intersections by about 80%.

* OK in the UK they have a red+yellow phase, but that just makes the consumption higher.  Other places only have 1 lamp lit at a time

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

Burra says I should mention the idea of using the Walker stove as a pure cookstove, and she's right, I should have .  On an otherwise warm or hot day we might want to use the stove for cooking, if for example we were out of gas or the electricity was off. (we normally cook in a mix of gas stove and combi microwave/convection oven)

By having the bypass available, it would be possible to light a fast fire with small sticks, and leave the bypass fully open, so minimal heat would stay in the house.  Under those conditions, half the hotplate on the stove would heat up quickly.  We also have lids we can open in the hotplate, one of which is right above the outlet from the core and would be great for boiling water or for setting a wok on to stir fry stuff.

I built a bypass into our Matt Walker tiny cookstove, and I wouldn't want to be without it.  However, I can see Paul's issue that if you have different people with no experience lighting the stove, it offers another way for them to get it wrong.

Here we live in a warm climate (compared to, say, Montana) and it can be chilly and damp so you want the fire alight but it's not ideal conditions for starting a rocket and then the bypass is a big help.  The bypass opening is approximately 6" x 3½" and is at the back of the core directly into the top of the brick flue just under where the chimney connects.  You can see it in my build thread

My normal lighting procedure is as follows:
1) make a small kindling fire (with cardboard or a pine cone or other tinder and thin, 6"-long or so sticks) right at the back of the box just in front of the secondary air tube.  With the bypass fully open it normally takes less than a minute to start that roaring nicely.
2) add full length fatter sticks and some larger pieces on top of those until the box is mostly full.  Those catch light at the end from the small starting fire, and in turn start roaring nicely.  As soon as that wood has caught I mostly-shut the bypass.
3) monitor the stove for a few minutes, especially the lower oven door, which is a plain 3mm steel.  When that door gets to about 26-27°C (78-80°F) the bypass can almost always be shut fully.

If, on a marginal day (e.g. bad wind direction or too warm outside), I shut the bypass completely too soon it can stall and belch smoke into the house which nobody wants.  This stall is unmistakeable: it will be burning fine and then quite suddenly will stop and clouds of smoke blow back from everywhere.  From what I see, this is due to the colder air in the lower spaces of the stove getting into the flue and reversing the temperature gradient.  

The other thing I would have built into my stove had I thought about it is flue priming access.  This would be a removeable plug of some kind at the bottom of the brick flue space near the back of the stove, and would allow for placing a small amount of cardboard or other tinder at the bottom of the flue.  I have a means to do that which is a small shovel on a long handle, which I can insert through the lower oven door into the bottom of the flue but that's more hassle.  Priming the flue like that makes a difference on marginal days when the outside temperature makes it hard to get the flue drawing.  Likely in a colder climate you'd find less use for that feature though.  In the same way, we don't generally burn the stove enough that it stays all that warm 24/7, so we do more cold starts than you would if you have freezing weather outside.

For what it's worth, I used refractory mortar on the lower part of the Matt Walker stove* that I built, which I don't anticipate ever needing to take apart.  The top layers are clay-sand mortar in case I need to get it apart for some unspecified maintenance purpose later.

One thing I keep noticing though is the clay mortar has very limited adhesion to the bricks when dried out.  It's easy to knock bricks loose.  I dunno if my clay is inferior or the sand the wrong sort or whether that's normal for clay mortar but it's something that might put me off if I'd paid someone to build a stove for me.  

For now we don't have a bench on ours, but it's in the pipeline once the space it needs to go into can be cleared.  Not a priority until the kitchen gets moved downstairs where the stove is and the focus of our life moves downstairs with it  The stove itself has a fair bit of mass, and is now working quite well after a few tweaks and experiments.

* documented here if you haven't already seen it.

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.

Fox James wrote:Twin wall, insulated stainless is very expensive for sure but, is a good investment for outside.
I quite often use single wall for anything inside and wrap it is basalt exhaust wrap.

On mine the first 45° bend on top of the stove is single wall as any heat there stays in the house; that joins to a double-wall insulated to go through the wall and then up the wall outside.  

I believe I'm fortunate in being close to a factory that makes the double-wall flues, and which sells to the permies.  A 1m length of 150mm/6in ID costs €75 including IVA (purchase tax), which isn't exactly cheap but it's cheaper than I was expecting it to be.

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.

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.

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.