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Rocket mass heating capabilities?  RSS feed

 
Ben Williams
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I would like to install one in a new construction. It will have supplemental heat via thermal mass (earthbag/cob) but the home will be rather large (1800 - 2000sf...ish) compared to some of the cottages that I have seen, in terms of square footage.
Because of that I fear thermal mass may not be enough.
I do live in NC and our winters are not nearly as cold as the more northern states but it does get chilly.

As of now I have decided that the flooring will be concrete and would like to perhaps run piping directly below before pouring the concrete.
I dont however know if this is a good idea or not.

My questions are...

Through how long of a pipe will air from a rocket mass stove continue to travel / properly heat?

Is there a size of stove / pipe vs desired square foot of warmth ratio guesstimate out there?

Will concrete block the heat too much or will it just take a little longer than cob?

Any insight and information that you can provide will be greatly appreciated.

 
Gary Park
Posts: 146
Location: St. Louis, MO
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My experience has been heating a 1500 sq. ft. house with a standard very inefficient wood stove located at the far end of the house in the basement(also 1500 sq. ft., so total of 3000), and I could go through a cord of wood a month in the coldest months and still have to supplement with electric space heaters. I'm currently gathering supplies and designing a rocket mass heater with similar sized piping(though my wood stove had an 8" flue, it really should have been a 6" for it's size). I have considered an 8" flue system RMH, but I think that would be overkill. Even a 6" flue standard wood stove puts out a TON of heat, so a RMH with a 6" should be even better. For my project, the RMH will be centrally located in the basement, and the thermal mass will cover ~46 sq. ft.(1 1/2 sheets of plywood sized) about 2' high average, with a 30 foot flue--using a 6"x30' stainless steel chimney liner. I will also be adding a cold air inlet which will help keep heat in the house. Overall, I expect to only be using space heaters set to where they may kick on in the morning at the most(not all of them on full blast 24/7 which cost me $200 last month when the lowest temp was about 35F! As for concrete blocking the heat, I'll be underlaying my setup with 1 or 2 inches of foam board, then 3/4 plywood. My cob mix will include some cement(which I think will keep cracking down when it dries), and I plan on smoothing it all over with that lightweight fiber concrete spackle stuff and painting or sealing it somehow.
 
Sam Surman
Posts: 64
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I'm all in favour of getting the most heat from the least fuel burnt ... at the moment we live in a reasonably well insulated house, with oil central heating and a wood stove to supplement additional heat.
The wood stove burns seasoned timber and puts up a good heat, I do burn it hot as that is best in a wood burner, I question if a masonary stove would be any better at heating (but I don't know) as the walls, floor, furnature etc all add mass to be heated at the moment, and the wall behind the stove is normally still noticebly warm in the mornings.
I feel that we would need to be burning more fuel (BTU's) to actually get more heat in the house, but perhaps the hot exhaust gases that are lost at the moment are were the savings in fuel would be ... but would they really make that much of a difference? I'd really like to see pics, vid's of actual rocket mass heaters in use in a home environment. Would be even better is folks on here could share their experiences and how they get on with them.
I would be interested in building something in our next home but don't really want to be experimenting, I'd like to build something that will do the job and do it well!

TIA
 
Gary Park
Posts: 146
Location: St. Louis, MO
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Dolman--I think a lot of people are in your position. My position is that if I don't step out and try it, I would be left struggling to get enough wood for a grossly polluting wood stove which had poor designs, too big uninsulated flue pipe causing a lot of creosote, burned through two FULL wheelbarrows full of wood a day(24 hours), and required multiple blowers and fans to get all the heat around. It was also located at the far end of the house against a concrete wall that was only partially underground, so that radiant heat was lost. I figured I had to redo the whole thing anyway, so here I go. One other factor was that a roof without a chimney is a lot easier to replace and less chance for any leaks(just replaced that section of roof and removed the flue piping).

On the factor of heating everything already IN the house for mass...most rocket stoves weigh a few tons. Mine will be probaby 6000+ pounds, plus a cinder block wall inches away that is freestanding in the middle of the basement. So for me, that trumps the kitchen table, t.v. and couches by about x10.

I would keep a wood stove I already had if it was nice, with a big viewing window, insulated flue, cold air inlet kit installed, and it had the afterburn air-injection option. Rocket heaters may be more efficient, but if you have something that is nice to use and look at already(and probably cost in the neighborhood of $2-3000 with the flue piping), then it would be REALLY hard to part with that for something made of mud and old oil tanks that doesn't have a lot of hard recorded R&D figures to go on.

What you COULD do is build a smaller one(maybe 2 pallets in the basement), and build it with stones, sand, fire bricks, and reclaimed materials to see how it goes(like the one on U-tube that they all moved with bicycles!). It will be a learning experience for anyone, just as installing and using a wood stove is. I remember installing my first wood stove and being so confused with all the clearance numbers, ceiling air gap spacer things, roof flashing, all the flue pieces, underlayment, wall heat shields, and then learning how to use the damper and air inlet slide valve thing, and then all the different kinds of woods and how they burn, and the moisture levels affecting that, and then overburning where all the paint would smoke up the house. It was so confusing and stinky and dirty and a pain to keep up, but I still have good memories of it, and now I could probably install a wood stove in a couple hours with one hardware store trip.
 
Sam Surman
Posts: 64
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tnx for that, and good luck with your experiments. I have a Morso stove with the 'after burn' or 'turbo' as I call it, and it works extremely well. But I had to show some faith when I purchased it as no one I knew had one and even the sellers knew/know little about it, but I'd never go back to an older stove again.
So perhaps when the time comes I might just have to bite the bullet again, but I'd like to hear much more about it from others that have actually travelled that road.

Cheers

 
dave marth
Posts: 50
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Im also wondering about the capabilities. I have a 800sq ft basement and 1000sq foot upstairs that was heated last season with a wood stove as the only heat. The wood stove radiated at 5-600 degrees though. Is a 6" rocket mass heater in place of the wood stove going to perform as well as a wood stove? I am just worried it wont have enough hot heat output to flood the house with radiant heat like my wood stove. It was a big moe by Vermont castings. It could take a 30" log.
 
L. Jones
Posts: 80
Location: NW Mass Zone 4 (5 for optomists)
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First, you make the most difference with proper sealing of the house against cold air infiltration and hot air exfiltration - ie, drafts. This is the most bang for the buck on almost every house, unless it was built VERY well VERY recently. Sloppy builders and old age (and ants and mice and a variety of things most people would prefer to keep out of the house) open up gaps - you have to seal them.

Next, insulation. The more careful and complete the better. If you have an unburied uninsulated concrete wall, FIX IT, don't just burn more wood/oil/electricity/gas. You should also fix buried but non-insulated concrete walls, though that does take a bit more work digging them out so you can apply insulation on the correct (out) side - but insulating the "easy side" is a heck of a lot better than leaving them uninsulated.

I haven't built an RMH, heck, as of a week ago I had heard of rocket stoves (cooking) but had not heard of RMHs. But...IF it's more efficient and you burn the same amount of wood, you should have more heat. I think someone mentioned a setup with a dual RMH - you could either assume you might need that and build both at once, or build one with space available to add another only if needed. Then you can burn one, the other, or both at the same time when you need more heat.
 
dave marth
Posts: 50
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I think what I'm worried about is it will be more efficient but I don't wanna have a trade off for a lower temperature in the house. What I'm trying to say is I know the rocket mass heater is more efficient than a wood stove, but I'm not sure if it will still put out enough heat to warm the entire house to a comfortable temperature. Also, I'm not sure if I'm going to have to constantly feed the fire as soon as it stops burning so that I can keep the house temperature up. Does anybody know what the Average temperature on a masonry heat riser for a rocket mass would be? I would assume if the bricks outside heat riser could get to the same temperature as my wood stove does then there would be no problem heating the house. What do you guys think?
 
Brent Rickenbacker
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I have been a user of both Rocket Mass Heater as well as a conventional wood stove in my home. I build my RMH out of an old water heater tank. It was fun to build and it did an OK job of heating the room it was in, but I found that it just didn't put out as much heat as my conventional wood stove. Here's a link to my rocket stove...
http://streetjesus.blogspot.com/2010/12/rocket-mass-heater-project.html

With a rocket mass stove you will burn less fuel, but you will find yourself feeding the stove more often.... Unless you can rig up some sort of gravity feed system. If you use your RMH within masonry \ cob you get the benefit of storing the heat in a thermal battery for an extended time.... My house is about 2900 sq feet, and the RMH just wasn't heating my house well. The room that my RMH was in got repurposed (Kids)... Sooo... Now my RMH is a patio heater. I am thinking seriously about cutting the top off of the unit and welding a flat top onto it with a hole for exposed flame for outdoor cooking.

This past year I installed a Vogelzang wood stove (The Durango. Got it from NorthernTool.com). I also added a device called a "MagicHeat" into the flue pipe. The new stove heats my entire house. The MagicHeat really cranks out a lot of heat. For the first time since my house was built it was actually warm this winter. I burned about 1-1/2 pickup truck loads of wood. I simply could not be happier with this setup!! Wood is abundant in my area, and I am going to build a wood shed to store my firewood for next winter!! Here's my new setup...
http://streetjesus.blogspot.com/2011/12/heating-with-wood-simply-best.html

Cheers!
 
Sara White
Posts: 1
Location: Ozone, Arkansas
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Greetings!

I am new to permies. I came here via rocket mass heater research. I was wondering if I could seek some sage advice from the ether concerning RMHs.

My husband and I are in the process of building a timber-frame house. It is approx. 1500 sq. ft. of active living space (1000ft downstairs, and 500 tucked into the gable peak upstairs). We will also have a 416 sq. ft. half basement. We're on a hill so it'll be a walk out basement on one side of the house, and a slab-on-grade on the other. Eventually we're going to have radiant heat in the slab (we're putting the PEX in when we pour), but we don't have the funds to set it up immediately. The floor plan of the main living areas is completely open. The house is set up passive solar with all of these living areas on the south side. The house is going to be well insulated (rigid sheets of extruded polystyrene).

My question is, will a RMH with a 40inch riser with a standard 55gallon drum top and 8 inch exhaust ducts running approx. 20ft heat a space this big? The bench I have designed is 28" deep by 18"tall by approx 20ft. Plus, the RMH is planned to be entirely on the slab-on-grade.

I've posted my RMH core design into Google Sketchup's model library if anyone wants more specifics.

Thanks ya'll!

 
I agree. Here's the link: http://stoves2.com
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