First Rocket Mass Heater Going In My Basement

Satamax Antone wrote:Matthew, your bell combination ISA is way too big for the 6 incher J you plan to use.

You have about 6.38m²

You don't can't use more than 4m² on a 6 inch J

It would be good for a 6 inch batch, and output a more heat.

Yea my original plan was to make an 8" system, but my chimney flue is a 6" essentially so i just figured i needed to do 6" for my rocket. So these numbers you are throwing at me are just the area of the bells and are not the total volume. So the height of my bells are of no concern? Please specify on how you got those numbers based on my drawing. I am a little lost on that. Any why i am now too big.



Also i don't know much about batch stoves as in how they work compared to a j-tube rocket. so building one i haven't looked into at all at this point. and as you might be able to tell i am no expert on rocket stoves or pyrodynamics at all. I knew i needed some criticisms thanks. so please people i want to be criticized. for i need it! for the love of my children and keeping their butts warm, lol.

-matt

Matthew, ISA or internal surface area is calculated as

Surface of every internal face of a parallelepiped exept the bottom one.

So in your case, (24+20) x72 x2 plus (24+12) x48 x2 plus 24x20 plus 12x24 = 10560sqin

If you have too much surface area, all the heat gets dissipated, not leaving any left to power the chimney, thus stalling the system.

I'm just transfering the numbers to you, from what i've read and remembered from Donkey's site. My bells all have been metal so far, and i have stalled a system once or twice. I admit, i also have restricted the chimney. Up to the point that i need a starting fan on my green machine.

Satamax Antone wrote:Matthew, ISA or internal surface area is calculated as

Surface of every internal face of a parallelepiped exept the bottom one.

So in your case, (24+20) x72 x2 plus (24+12) x48 x2 plus 24x20 plus 12x24 = 10560sqin

If you have too much surface area, all the heat gets dissipated, not leaving any left to power the chimney, thus stalling the system.

I'm just transfering the numbers to you, from what i've read and remembered from Donkey's site. My bells all have been metal so far, and i have stalled a system once or twice. I admit, i also have restricted the chimney. Up to the point that i need a starting fan on my green machine.

alright so i did some calculations. the math you sent me now makes a bit more sense, but i have been following this build at dragon heaters. so im a little lost still after a crunch of their flue dimensions vs. mine. here is the blog i have been looking at.. http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-2/ and if i use the dimensions from the kit they sell.. http://www.dragonheaters.com/6-rocket-masonry-heater-castle-build-kit/ ...my numbers don't seem too far off if i line the inside of my first bell similarly with lets say a 16"x20" liner to the top. the ISA would be 9,248sq. in. which would only be 67sq. in. different from their tested build. which according to them was fairly draft friendly even in hot weather. so i guess im not sure where your coming from exactly. i mean if the build i provided the link to actually works well as advertised i cant see why mine wont work even if i somewhat loosely follow what they did. if you could provide some information to help prove your statement to me that could be helpful. it almost seems your stalling might be coming from your restricted chimney alone. im no expert as i already stated, so i would like to clear the air(smokey) so to speak, lol. i appreciate bringing up the point regardless of my understanding with it.

-matt

Peter Berg wrote:

matthew boersma wrote:i think/hope this is what are saying i should do?

Yes, you've got the picture.
Don't know what size the bells ought to be, when too large you are loosing too much draft and the "thing" will backfire.

As an afterthought: when quick heat isn't required there's the possibility to build the rocket inside the first bell and skip the barrel.

any thoughts on the above notions? btw are you peter van den berg by chance? the guy they mention in many of dragon heater designs. if so, im sure you have some knowledge/expertise based on this design. please help!

-matt

also i would like to add i noticed that in that specific construction the inlet/outlets are much larger than the 6" exit point this is built for. more like about 10"x 8" from the heat riser to the first bell and about 12"x12" to the second as it looks anyway. so i am wondering if as long as the feed is about 6" construction and the exit is 6" construction will the "free gas movement" system work fine as long as there are no smaller restriction point along the way. these guys seem to think they have great drafting in this system. like i asked.. any thoughts?

matthew boersma wrote:it almost seems your stalling might be coming from your restricted chimney alone.

Please note: any chimney however perfect, could be stalled by a low exhaust temperature and lots of moist in the flue gases. Mine did this several times anyway.

btw are you peter van den berg by chance? the guy they mention in many of dragon heater designs. if so, im sure you have some knowledge/expertise based on this design. please help!

Yes, my full name is Peter van den Berg or PvdB for short. The rocket heater cores sold by Dragon Heaters are my design and some of the ideas incorporated in their complete stoves are mine as well. But they did their own development and testing to find out what would work and what not regarding their bell designs. So I don't have hard figures to share with you, sorry.

also i would like to add i noticed that in that specific construction the inlet/outlets are much larger than the 6" exit point this is built for. more like about 10"x 8" from the heat riser to the first bell and about 12"x12" to the second as it looks anyway. so i am wondering if as long as the feed is about 6" construction and the exit is 6" construction will the "free gas movement" system work fine as long as there are no smaller restriction point along the way. these guys seem to think they have great drafting in this system. like i asked.. any thoughts?

The transfer opening from the riser to the first bell in the Dragon Heaters design need to be larger than system size because of the high temperatures. Also the openings were dictated by the size of the liners itself.

The transfer holes between two bells could be as small as system size itself, provided all around the circumference the gases can stream through. When such a hole is placed really on the floor of the bell, around a quarter of the opening is blocked by the floor, so the opening has to be larger accordingly. There is a way around this: when the opening is placed higher up, about half the diameter of the hole, gases are able to stream through all around the circumference. Moreover, when you choose to use a rectangle opening this has to be substantiously larger in cross section area because the corners are virtally useless for smooth streaming of gases.

Every shape and placement has its merits and problems, it's not easy to recognise built-in restrictions even when it won't look like that.
Round is best, second best is square but has to be larger in csa, rectangles are worst so those could end up as twice the area as the round one, especially when placed in a potentially troublesome spot. When you know all this, it seems logical to cut out a complete side of the liner, don't you think? Could never be too small.

so to update everyone i do plan to move ahead attempt a build outside model with the parts first. not mortared at all though, and probably just using ceramic felt in the gaps to make sure there are no gas leaks. i am hopefully finishing the cast form today and casting as soon as i have the chance. i still need to find a good way to vibrate the mold without a vibrating table, and also i have a mixer coming so i can make sure the mix is mixed proportionately. i will post pics of my process as soon as i get them as well.

i do have a few concerns which is why in the first place i am planning on building a test model outside. even though i may get a solid test run if things go well i am now thinking about how differently things will act piping into my actual chimney inside the house. i plan to emulate the size of my chimney outside in my test with the same size flue that is already lining my existing chimney to hopefully to get a good idea of how my draft situation will be. the main difference will be the outside model will have a much shorter chimney than the one in my house.

my house chimney is from the basement floor to approximately 6 feet high. through my main floor of 7.5 feet to the ceiling. through the upstairs of about 7 or so feet again, and then finally through my attic and out my roof probably about another 10 or so feet in total from there. so an approximate total height of the chimney would be close to 31 feet give or take a foot or two from basement floor to out of my roof. and it travels through the very center of my home so this should have a great pull for draft hopefully. i plan to pipe into my chimney on the main floor at floor level so about 7+ feet from the very bottom. my question is do you think this will be a problem piping in so high. typically i have seen pipe in locations in the basement at about half this height. will there be a problem with cool gases or some sort of smoke settling down at the base of the chimney? i guess my thought was typically in a very common situation the gasses are much hotter by up to 3x or so possibly going into the chimney. so i would imagine the draft would carry them out very easily and quickly. my exhaust temp if the design works well should be about 150 to 200 at most ensuring i am not just loosing my created warmth to the outside. i will have the chimney sealed down in the basement at the existing port areas. they will be closed off so my draft works on my bell system and not the basement air. so any thoughts on this? should i close of the lower 7 feet of the chimney at all. or would you think the draft will be good enough to carry all of my exhaust out my my house adequately? thanks once again in advance.

-matt

matthew boersma wrote:i will have the chimney sealed down in the basement at the existing port areas. they will be closed off so my draft works on my bell system and not the basement air. so any thoughts on this? should i close of the lower 7 feet of the chimney at all. or would you think the draft will be good enough to carry all of my exhaust out my my house adequately? thanks once again in advance.

Hi Matt,
That lower 7 ft of chimney is far too much dead end to my taste. The draft caused by upper end of the chimney will pull some of the air out of that dead end pipe and create a slight under pressure in there. This will act as an inhibitory effect, like riding in a car with the hand brake on. As a rule of thumb, the length of the dead end in the chimney shouldn't be more than the diameter of the same.

Peter Berg wrote:

matthew boersma wrote:i will have the chimney sealed down in the basement at the existing port areas. they will be closed off so my draft works on my bell system and not the basement air. so any thoughts on this? should i close of the lower 7 feet of the chimney at all. or would you think the draft will be good enough to carry all of my exhaust out my my house adequately? thanks once again in advance.

Hi Matt,
That lower 7 ft of chimney is far too much dead end to my taste. The draft caused by upper end of the chimney will pull some of the air out of that dead end pipe and create a slight under pressure in there. This will act as an inhibitory effect, like riding in a car with the hand brake on. As a rule of thumb, the length of the dead end in the chimney shouldn't be more than the diameter of the same.

got it. so block the lower 7 feet off somehow then?

-matt

matthew boersma wrote:got it. so block the lower 7 feet off somehow then?

Correct. Maybe by making a horizontal slit in the side of the chimney and sliding in a wide piece of flat steel?

Peter Berg wrote:

matthew boersma wrote:got it. so block the lower 7 feet off somehow then?

Correct. Maybe by making a horizontal slit in the side of the chimney and sliding in a wide piece of flat steel?

what if i make this slit about a foot or two lower than the inlet into the chimney. such as at ceiling level in the basement. so i can pull it out and let any ash that might collect fall down to the original ash clean out at the very base of the chimney. do you think that could work ok?

-matt

Matthew B. : What you are describing should be airtight and then would be called a guillotine plate, My question is -will you have to remove
or disassemble the stove pipe to pullout the handle of your guillotine ? I would be very surprised if you get a quart full of fly ash in a heating
season, unless you are also blasting a lot of heat out doors. A stovepipe "T' With a clean out at the chimney would probably serve you just as
well .

Also now is your best time to ask for second opinions on a Rocket Mass Heater in your basement ! for the Craft ! Big AL

here is my prototype mold innards. i realize a few things already measuring it out again. first off you might notice that my "P-channel" is taken out of the feed opening area. i think from what i understand in reading about how to incorporate it that it is to be 5% of the feed opening area added to the top end of the feed for an "added" air channel. clearly i forgot when making this model and notched it out of the feed area instead. so correct me if i am wrong.. i should fix that? also i made the top on the p-channel opening larger than the bottom as you might also notice so hopefully this will act as its design suggests.

my innards are 5 3/8" x 5 5/8"(i have accidentally put 5 6/8" by accident so note that if you decide to calculate my flow space). if designing this to fit into an 6"(my square clay flue liners in my chimney are about 6.25"x6.25" or so)" system i need to have a cross sectional area of 28+ square inches(pi*radius squared). with this i have 29+. so being this j-tube is square in shape i probably will have a slightly less area than that for air flow since circles are better than square by a small bit, right? so if is all well so far i also have a concern about the pitched roof of the burn tunnel as well. i took a 1" foam board and shaved down the sides at an angle to create the pitch. this will add slightly less than 3 square inches to the area in the burn tunnel i believe. although i haven't tried to calculate the effected area of the ramp to the "kick tail" yet, or not sure if i really need to. it seems to look good to me. and i was thinking it might not be a big deal in widening the cross-sectional area of the burn tunnel because the "trip wire" does somewhat act as a truncator bring the flow are back to a similar number as the rest of the system. not sure about that?? obviously i am basing this around peter's design as so many of us are from what i can tell. i don't want the engine too big so my chimney cant draft out the smoke properly which is why i went with slightly less than 6"x6" to begin with. also assuming my bells create the right draft when operating, but from i am reading bells tend to create a quite good draft scenario as long as my inlet/outlets are big enough. please let me know what you think.

-matt

side view, top view, front view

close top view of p-channel and trip wire, and close side view of the same

Peter Berg wrote:Every shape and placement has its merits and problems

i plan to split this in half when completed to satisfaction and cast similar to how you have shown in your donkey32 posts. thanks for being such an icon in this community. or at least to me! let me know what you think about my decided dimensions.

-matt

anyone by chance have an idea if i am going to have success? first build working great is what i need. i cant really afford to mess it up.. i already have spent too much on materials sadly to say. not too much to justify the project. if it works it will give me great savings in the first year i believe. i just am running out of funds to do much more.

-matt

here is a slightly updated model on a few of the areas. also with a few more dimensions posted.

-matt

Matt B. : i see nothing that jumps out at me, The single most important is to build your 1st rocket as conventionally as your materials will permit ! Generally your 2nd
or 3rd build is soon enough to try and improve on a well established pattern >

I expect that you will have success and someday soon you will be the one giving this information to another would-be-jr.-Rocketeer !

Remember to dry fit everything outdoors 1st, fire it up, and make sure your design will work in the space and with the parts you can give it , then finish your build inside!
Big AL

Matthew, to me there's plenty of details i'm not too keen on. The kicktail seems extremely fancy. The ceiling of the burn tunel is not flat, tho i like the idea. The two side parts of the tripwire i would remove, that leads to a reduction in csa. The tripwire seems too deep. And the burn tunel too long. But that's just my impression.

Satamax Antone wrote:Matthew, to me there's plenty of details i'm not too keen on. The kicktail seems extremely fancy. The ceiling of the burn tunel is not flat, tho i like the idea. The two side parts of the tripwire i would remove, that leads to a reduction in csa. The tripwire seems too deep. And the burn tunel too long. But that's just my impression.

well i agree.. im still tweaking the mold. i have removed the point to the kick tail, so now it is a bit more rounded(this was peter's suggestion). although i am thinking of slimming it(the kick tail ramp) down just a touch more so its not so drastic. i also was thinking the side trip wire is a bit much. so i could easily make it much much smaller or nonexistent. i will say that my pitched roof does add about 1-2 square inches to the c.s.a. so i was thinking i should be safe as long as i don't over do the trip wire concept. i have been molding it fairly closely to the dragon heater core i will admit. they include all the "features" that mine resembles on theirs. my core dimensions may be not exactly what they are using, but from their overall listing of the outer core dimensions(or at least from what i can tell) i am somewhat close i believe. also i have compared my tunnel length to a blown up picture(i know its not exact) by blowing it up with my core up against my computer screen(lol) and have found that my ratios are near exact from what the 6" dragon is. i don't necessarily believe that the used dragon heater design is the one and only best out there. i just have read their testo graphs and cant really deny that they are very impressive. too much money for me if i can use my handy skills to come up with something close that will hopefully work as well or if im lucky.. better. thanks for your criticisms. please do not hold back if you have any more. to success!!

-matt

hey all, i am about to cast my core in a day or so. i am using kast-o-lite 30li for the refractory cement. i have already built molds out of plywood for both the core and riser. my molds are measured out to be about 1.25 inches for the outer wall thicknesses. my question is.. would you think 1.25 inches is a good enough thickness(or should i really go bigger? i have a vibrator unit so i am looking to get very solid casts. also i have noticed after squishing in my riser innards foam part that my riser dimensions are likely to be about an 1/16" more on at least one of the sides. any perceivable issues there (i was thinks at least it isn't much of a difference and not smaller)? any thoughts?

-matt

Anyone... Or yall too busy at the workshop. Looks like fun. Wish i was there.

matthew boersma wrote:hey all, i am about to cast my core in a day or so. i am using kast-o-lite 30li for the refractory cement. i have already built molds out of plywood for both the core and riser. my molds are measured out to be about 1.25 inches for the outer wall thicknesses. my question is.. would you think 1.25 inches is a good enough thickness(or should i really go bigger? i have a vibrator unit so i am looking to get very solid casts. also i have noticed after squishing in my riser innards foam part that my riser dimensions are likely to be about an 1/16" more on at least one of the sides. any perceivable issues there (i was thinks at least it isn't much of a difference and not smaller)? any thoughts?

-matt

I do not have experience with casting, although I am making a mold right now. I would think that 1.25 is a good thickness, like the "split" fire brick.

I would think that it is not good to make it too thick, as that could cause cracking with the expansion. But that is just my guess.

One think you may want to do is to cast a small brick to as a test to get familiar with the Kast-o-lite, and to see how strong it is.

I notice you are casting a square riser. Peter's original model used a vermiculite board, as do the Dragon Heaters. The Lowes in this area sells vermiculite board in 36 inch squares at 3/4 inch thickness for a good price. (If you have to get it mail order, it is very expensive, since they have to make a special crate to ship it.)

I think the vermiculite is a better insulator. But if I was going to actually cast the riser, I would make it round.

But again, I don't have experience with this.

- joe

So here are my casts. Came out pretty well. Seems extremely sturdy. I will be trying to bake cure the j-tube in my oven. Although my max temp in there wont be what it will be when im building a fire in it. So im not sure this is a good idea or not. Should i bother? Or should i just start with a small fire right away and build to a roarin one? My riser is 30inches tall, so i will have to just use the workomg unit to heat cure with fire. Any suggestion on a further cure for this kast-o-lite 30?

Will be putting a test dry build together of the whole masonry heater this weekend hopefully. So time is soon for seeing if my time and money will pay off.

Hi Matt,
you asked me to weigh in again on the question of the steel barrel vs. starting the masonry bell right over the firebox.

I also noticed the question about 6" vs. 8" systems. Since you now have a beautiful 6" cast firebox ready to go, that seems like the way to go for now.
If you have any trouble that leads to needing to replace that firebox, you might look at Peter's 6" batch box designs. They may be able to give you a little more heat while working with the same size chimney.

The main value of the steel drum is that it's easy to install, and also relatively easy to remove if you need to get in there and mess with things. It's also usually cheaper than brick, though in your case it sounds like you have a lot of reclaimed brick available.

The instant-response heat is a benefit if you have the heater in the living area of your home or cabin, and sometimes take a winter vacation. It's less valuable if you're trying to maintain steady temperatures (heat will increase during the fire with a thin-walled steel bell), and if you plan to run the heater regularly enough that you never come home to a cold house. It's a problem if you have to put the firebox in a small room for some reason, or outside the occupied areas of the building. (for example, if the intense radiant heat off the barrel would lead you to putting it in a different room to avoid scorching plants in a greenhouse).

If it were up to me, I'd probably lay out your system as two parts, with the two permanent bells as you showed them to the right, and the combustion unit to the left. Give yourself room to get into the firebox area, and raise the openings up a few inches off the floor of the bells, so you can get in there easily and clean out any fly ash or take a look at any problems.

Now that we have a layout that we can alter if needed, I would consider using the barrel for this year, so you can open it up and look at things next spring before making a final decision.
To use the barrel, you'd build the brick box up to the right height to support the barrel with at least 2" gap above the heat riser (Peter might say 3" to 4"), and use just clay-sand mortar to seal the barrel onto the last course of brick. (You can do one course with bricks angled across each corner, to make an octagonal shape that meets the barrel rim easily.
Fill any holes in these bricks with mortar, or use solid bricks for the last course. Add several inches of plaster or cob (earthen masonry) around the outside to completely seal all joints, since this high-temperature area may get a lot of steam and expansion strain. You could wrap some mineral wool insulation around the rim of the barrel to reduce expansion strain if you want, or fire the heater while the cob is still pliable to set it at the expanded size.

To skip the barrel, you'd continue building upward with bricks to above the level of the heat riser. The bricks won't facilitate downdraft like the barrel does, so you'd continue upward a little farther, and make a fairly tall space above the heat riser. This lets hot gases lose some heat due to stay time, and cooler gases flow down. It may also relieve some of the extreme, concentrated heat immediately above the heat riser. For a short bell over the heat riser I'd expect thermal expansion in the center to cause a lot of strain, possibly cracking the top slab. You can account for this by using multiple units like bricks or half-slabs, in layers, so that the cracks are built-in and the construction remains self-supporting over the gap. Or use a very insulative, slightly flexible material for the top slab, and give yourself a way to inspect it for leaks or damage as needed. Whatever you use, think in layers, with a relatively easy way to inspect and repair any leaks that might develop due to heat, time, or household accidents. (Someone once dropped a partially-built roof on top of one of our first stoves, for example.)

As Satamax pointed out, regular cement mortar is not a good choice for the hotter parts of this system. We like to use the traditional clay-sand mortars, because it means you can take things apart and re-use the same bricks, and clay is also very similar to brick in terms of thermal expansion so it's less likely to have differential movement and cracking problems. There are also refractory mortars available which form a more permanent bond; but in some cases these harder materials require a better understanding of thermal expansion to have good results the first time.

I suspect your two bells could just as easily be built as one bell, if you can find or cast a suitable capping slab. Peter likes surface area rather than volume as the basis for calculating heat absorbtion, and given the chance to witness his excellent experiment last month, I would go with his numbers. Include the surface area of the bell or barrel directly over the heat riser, as well as the other bell(s) on the side.

Having laid all that out, I confess I have never successfully built a masonry bell. I have built lots of brick beehives to support a steel barrel, but the thermal differences at those lower areas are only a few hundred degrees F, not enough to cause serious materials problems that you might encounter directly above the fire.
It might be an extremely good idea to look into the traditional masonry heater designs available online, in David Lyle's Book of Masonry Stoves, or any local examples or builders you can find, to get a better idea how to do those capping slabs or brick-built domes over the spans of their stoves. You might find a design that just feel right, and has been proven out over centuries, to fit your needs.

This message might need to be edited later; i'm trying to squeeze a complicated response into a busy day. Peter or Lasse, any corrections welcome.

Yours,
Erica W