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How to install an RMH in a home without it looking like a hatchet job

 
pioneer
Posts: 198
Location: Chesterfield, Massachusetts, United States
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One wants to be both warm and surrounded by beauty. Bare-bones RMH's seem to be fairly um...well they're not my idea of aesthetically pleasing. The curvy, wobbly lines of a cob-structure look very odd and out of place in a stick-framed home built in 1860, or at least they do in my opinion (read: I don't want to argue about the aesthetics because I like not losing apples). Has anybody come across a more aesthetically-pleasing design approach to an RMH that leverages the benefits of the excellent efficiency of an RMH but does so in a more muted, less cob-forward way? To be clear, I don't mind using cob, I just don't want to have a giant 10-foot long bench of cob looking weirdly out of place in the corner of a room.

Another question I have is about positioning. RMH's have to be vented out the SIDE of a building like a dryer vent-line, not up a smokestack, correct? If I try to vent it upwards, I risk gassing myself with CO2, is that accurate? I ask because our home is an old colonial-style, so the downstairs is 4 equally sized rectangular rooms, and the upstairs is another 4 equally sized rectangular rooms. There is a kitchen built off the side of the downstairs and then a computer den off the side of that, and above the kitchen/computer den is a little rec room where we have our pet bunny rabbits. It's a lot of space to heat, so I fully anticipate needing more than 1 RMH if I really intend to use all that space in the winter.

Fortunately, each of the upstairs rooms and 3 of the downstairs rooms has an old fireplace that has been boarded up. There are a WHOLE BUNCH of chimneys on this house. I would never re-open them just to build a fire in a fireplace, but if I'm able to vent UP from a rocket mass heater, that would sure be a great boon to me as I could build the RMH in a hemicircle around the existing fireplace, thus minimizing the footprint of the RMH creeping into the useful space of the room, *and* I wouldn't have to put a new hole in a 160-year old house. But if it really needs to vent out the side, I will have to do that. My question is how much square footage should I anticipate dedicating to each RMH? We're talking over 3000 square feet of space that needs heating.

So here's a THIRD question (figured I shouldn't do a separate topic for each): How much square footage does 1 RMH heat? I imagine that depends on how big you build the mass and how big of a firebox you allow for the rocket. But is there a sort of standard model of RMH that permies has settled on? How many square feet does that occupy? What is the equivalent BTU that it outputs would you say? Do the BTU's from an RMH cover a volume of space as efficiently (or better) than a space heater or a furnace or some other standard form of heating? I.e. if 10,000 BTU from a space heater were to cover a 10x10 room, would 10,000 BTU from an RMH cover the same volume? (I don't have any idea if those are reasonable numbers, I'm just giving them as a 'for example')

I don't have exact measurements on all the rooms, but it's around 15x15 in each room in the Colonial, old-school part of the house (the part arranged like 4, equal-sized boxes). The kitchen is maybe 20 feet long by 12 feet wide, something like that. Totally forgot to even draw in the office which is just off the side of the kitchen in front of the old barn structure which is attached by a back hallway that is allegedly haunted and is my favorite weirdo feature of the house.

Any rate, as I said, I know we are talking about beaucoup square footage, so this isn't going to get done with 0.6 cords of wood or anything like that, but I'm going through like $250/month on heating and it would be super great to stop doing that. I imagine even if it took 2-3 cords of wood, given that I've got 7 acres, I probably could harvest that sustainably myself for free and just keep a stand of trees in continual coppice.

This house also has a large, unfinished, dirt-floor basement with a mix of fieldstone and brick-and-mortar foundations. It's currently got an old, shitty, inefficient oil furnace for the downstairs heating and a more efficient (but still not as efficient as RMH) Buderus gas furnace for the upstairs part of the house. We were going to get rid of the oil furnace and revamp the downstairs with gas too, but if we can strategically place an RMH or two and keep the downstairs balmy on wood scraps, that's way better than using dinosaur farts. The basement spans the entire length of the house's footprint and is shored up with a ton of metal support beams sunk in concrete footing and buttresses on parts of the foundation wall. I have seen elsewhere that building an RMH in a basement is not recommended, so I'm not thinking that space is probably usable, but we do plan on drying it up, finishing it a bit (either a slab floor or maybe rammed earth or clay or hempcrete) and using it as a root cellar for our foodstuffs once we get more permie production going. So if that space would be useful for the purpose of heating the house more efficiently in some way, by all means, I'm willing to do whatever it takes to get to carbon neutrality and then carbon negativity.
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gardener
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Location: Westbridge, BC, Canada
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Hi D.W.

Rocket mass heaters come in a wide variety of skins that appeal to various tastes. Have you seen any masonry ones? Brick and stone give a real nice solid and angular appearance.
Wood accents applied to cooler areas of the bench can also add a nice highlight. Cob doesn't need to make up a large portion of a build but is real nice and forgiving to use when working around areas that need odd shapes to fill.

In the early days, Ianto Evans popularized through the wall chimneys that worked well in his tiny, single level home with very specific circumstances that allowed the gases to flow properly.
In a 3 story home like yours, forget it. You would end up with more smoke back in your home and will make you want to rip it out.
A properly insulated chimney that clears the highest peak of the roof by a few feet is almost always what is recommended, if not mandatory.
Your idea of multiple stoves sounds like a great idea, you just can't share the same chimney pipe for them all. If the stack can accommodate a separate stack for each stove that would certainly work - which is what sounds like is already there from your description.  

The amount of square footage each stove will take up really depends mainly on how much mass you want to add and whether its a bench or a tall bell chamber(s).
Peter van den Berg has posted some information on his website to help calculate the size heater that is needed to help heat your home. These numbers of course are related to batch boxes but may give you an idea if you are looking at making J tube rmh's.  How to size a batchrocket

Do know that when you build on the upper levels, keep in mind that you are going to be dealing with several tonnes of weight, so make sure you plan your builds accordingly to handle these kind of loads.
 
gardener
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Location: Cincinnati, Ohio,Price Hill 45205
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Definitely take a look at Donkey's forums https://donkey32.proboards.com/

Peter is a regular,  along with Matt Walker.

Where do you hang out most , which room?
I would choose that room and install a 6" batch box or 8" j-tube.
Once you get that one working and the bugs ironed  out,  I would build smaller one in the next most favored room.
Smaller rockets are more fussy, but if you are planning on one per room,  they might be the way to go.


Do your existing furnaces have a return air ducts?
Building a rocket mass heater in the room where a return air register is could let you spread heat from a central location via existing equipment.
 
pollinator
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Location: Hamburg, Germany
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Not to discourage you from building your own RMH, but have you looked at masonry stoves to meet your aesthetic (and have a pro install it, if that's an upside for you)?

In Germany they're called kachelofen - Wikipedia page here: https://de.wikipedia.org/wiki/Kachelofen (in German but Google Chrome will translate on the fly)

I know nothing of this company except that they have a nice mix of modern and old-fashioned styles:  https://www.kachelofenwelt.de/design/bildergalerie/kachelofen-heizkamin/
Or in the US:  https://www.mha-net.org/html/gallery2.html
 
D.W. Stratton
pioneer
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Location: Chesterfield, Massachusetts, United States
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Morfydd St. Clair wrote:Not to discourage you from building your own RMH, but have you looked at masonry stoves to meet your aesthetic (and have a pro install it, if that's an upside for you)?

In Germany they're called kachelofen - Wikipedia page here: https://de.wikipedia.org/wiki/Kachelofen (in German but Google Chrome will translate on the fly)

I know nothing of this company except that they have a nice mix of modern and old-fashioned styles:  https://www.kachelofenwelt.de/design/bildergalerie/kachelofen-heizkamin/
Or in the US:  https://www.mha-net.org/html/gallery2.html



A cursory look at the Internet seems to suggest they range in cost from $6,000 to $30,000 per stove. That seems prohibitively expensive for me.
 
pollinator
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Seems like the questions are

Load-bearing capacity of the basement's metal posts and floor itself

How to determine if the chimney is insulated and sound

How to make a visually pleasant cover for the bench


Cottage rocket (lightweight) might be worth making as a first pass.  Also a chance to try out  decorating it, and get a feel for how warm it is.  A blanket over a cob surface, assuming it's safe, could be aesthetic enough for the immediate situation.

If the chimney is not insulated up along its length, perhaps you can get insulated stovepipe (I think I've seen that sold) and just insert.

The balance is between safety and cost and so on.  Since we're in a pandemic, and getting a hold of contractors can be extra difficult, maybe it can be worth letting the aesthetics slide for this year.  

Also, "use slow and small solutions" comes to mind.  A cottage rocket as a start, then it can be expanded when you are able to get the basement supports evaluated/supplemented.

I'm no expert here, just speculating.

 
Joshua Myrvaagnes
pollinator
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oops, just to be clear, I had in mind a blanket over the bench of a _regular_ rocket mass heater, NOT over a cottage rocket.  Kids, do not try this at home.
 
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To my ever so limited mind...
A batch box feeding a bell....used as a wall between two rooms has always seemed like it had great potential,
Both to be aesthetically pleasing, and double your exposure of heated surface to two rooms at one burn!

If, (and mind you I'm stretching past my experience here) multiple floors had common wall lines a multistory bell could potentially expose 6 rooms over three floors to one batch box.
If overcooling the smoke was a concern then a narrow wall say four foot broad with a torturous path to ensure contact could still expose each room to heat.......
 
D.W. Stratton
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Bill Haynes wrote: To my ever so limited mind...
A batch box feeding a bell....used as a wall between two rooms has always seemed like it had great potential,
Both to be aesthetically pleasing, and double your exposure of heated surface to two rooms at one burn!

If, (and mind you I'm stretching past my experience here) multiple floors had common wall lines a multistory bell could potentially expose 6 rooms over three floors to one batch box.
If overcooling the smoke was a concern then a narrow wall say four foot broad with a torturous path to ensure contact could still expose each room to heat.......



Not quite sure I understand you. Any chance you'd draw a simple sketch of this and post it?
 
gardener
Posts: 3183
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Bill's idea of replacing the wall between two rooms with a (brick?) bell RMH is a good one, and a two-story bell is feasible too, as long as the system is sized large enough to heat that much masonry.

That said, the devil is in the details, and from the very rough sketch and a general knowledge of how old houses are often built, I am not sure that is practical here. We need to know a lot more about the layout of the walls, stairs, doors, and which way the floor joists run. Ideally, I would put the bell between the craft room and dining room for best centralish location and heat distribution, extending up through the floor to heat the front bedroom and two baths. However, I suspect that wall is load-bearing and you would have to do major structural alterations to accomplish this.

The next best location might be between the living and dining rooms, possibly extending up. This may require a minimum of structural rework to the framing, but I am not sure it is possible to use that location without obstructing the stairs and/or upstairs hallway.

In any case, with the basement as rough as you indicate, putting in piers or block walls to support a massive bell at ground floor level seems not a big deal. Depending on hall/stair configuration, a central bell on the ground floor might be able to heat the upper floor sufficiently. I would locate the bell and the firebox feed in the room you use most, and also as close as practical to a back/side door for wood transport ease. You will be carrying wood every day, make it convenient. If you have easy access from wood storage to the basement, you might build a large batch box there with a bell extending up through the floor to heat the ground floor. This could incidentally make the basement relatively comfortable. A batch box does not need frequent tending, so a good one in the basement could be practical to operate.
 
D.W. Stratton
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So what I'm hearing is there is no cheap way to switch to any kind of rocket heater for this property...

I know absolutely zero about house construction. Wouldn't know how to tell you a thing about the walls. And if any engineering needs to be done, we are probably jumping right to the five-digits for pricing. Can't afford that.
 
Glenn Herbert
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A large house with basement is going to require some foundation to support a mass on the first floor, but that does not have to be a complicated thing. Can you see the floor joists in the basement ceiling? Do they run from the front wall to a beam under the wall between craft room and dining room? If so, then that wall above will be load-bearing and you would not want to cut it away without resupporting what is above. However, you would not need to make a very large hole in the floor, maybe 4' x 3', to accommodate a bell with clearances. Cutting just on one side of that wall rather than down the middle would avoid replacing the main beam. Supporting the cut floor joist ends with the block foundation for the bell would be easy for a carpenter/builder, if you are not confident in doing it yourself.

Where are the fireplaces (and chimneys)? That is obviously a major consideration, and may make bell location easier. A more detailed sketch of the ground floor, with doors and fireplaces noted, and room dimensions to the nearest foot, would allow us to give some useful advice on what you could actually do. With details of the ground floor layout, we could concentrate on parts of the basement that need to be investigated for clearances.

I do think starting with something like a cottage rocket in a main room, to see how you like the operation, would be sensible. While you are using that, you could develop plans for a more ambitious whole-house RMH.
 
Bill Haynes
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Well...
I dunno if your drawings are to scale but from a cursory look it seems that you have a common wall between the living and the music room that carries through the second floor bedrooms.
If a brick bell was built on the bottom floor with a batch box (preferably in the music room since it has outdoor access) carrying through to say at least 4' above the average floor level on the second floor you would have good exposure to four rooms.
At the least if building a 4' wide bell it would entail removing one stud from the lower wall and half of one stud from the upper wall, and the addition of a steel beam (supported by the bell itself!) to support the upper  floor.
Alternatively it could be built against the wall, and the wall covering removed to expose the second room to the bell leaving he studs in place, but that seems like a far from handsome alternative.

The caveats are;
You need a solid foundation clear down into the earth for that much masonry, no stretch of the imagination will allow such tonnage to depend on framing.
$ 8,000 to $ 10,000 USD does not sound unreasonable if no unforeseen circumstances arise. Average heating costs run $1500 to $4000 yearly so the pay off is well within five years.
A sane man intending to occupy the home for generations would pay an engineer to ensure adequacy.
 
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D.W. Stratton
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Bill Haynes wrote:Well...
I dunno if your drawings are to scale but from a cursory look it seems that you have a common wall between the living and the music room that carries through the second floor bedrooms.
If a brick bell was built on the bottom floor with a batch box (preferably in the music room since it has outdoor access) carrying through to say at least 4' above the average floor level on the second floor you would have good exposure to four rooms.
At the least if building a 4' wide bell it would entail removing one stud from the lower wall and half of one stud from the upper wall, and the addition of a steel beam (supported by the bell itself!) to support the upper  floor.
Alternatively it could be built against the wall, and the wall covering removed to expose the second room to the bell leaving he studs in place, but that seems like a far from handsome alternative.

The caveats are;
You need a solid foundation clear down into the earth for that much masonry, no stretch of the imagination will allow such tonnage to depend on framing.
$ 8,000 to $ 10,000 USD does not sound unreasonable if no unforeseen circumstances arise. Average heating costs run $1500 to $4000 yearly so the pay off is well within five years.
A sane man intending to occupy the home for generations would pay an engineer to ensure adequacy.



If the basement hasn't got such a support, can one be retrofitted in place if the basement has a dirt floor?
 
Glenn Herbert
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It would be easier with a dirt floor than if there was already a concrete slab. A serious load like a two story plus bell would most likely overload and crack a standard basement floor slab, but a properly reinforced spread footing on bare dirt could take the load fine.
 
Bill Haynes
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With enough zero's on a large cheque everything gets easy!

Yes a dirt floor would be an ideal starting ground, ...and much of the work could be done by yourself.....but we are far past my education.
A competent bonded engineer is needed to do soil tests, and tell you how broad and deep your foundation needs to be, concrete content, and reinforcement minimums, and then you, (or your agents) can build to those specs.
Anything less, and you're tempting fortune to kick your hiney!
 
pollinator
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Considering the snow has already flown many places...

I would get one of these

https://www.rocketheater.com/buy-a-rocket-heater/

Not pretty, but efficient and UL listed if you need that for zoning or insurance.  And quick.  It is a good solution for upstairs regardless because it is fairly light.  

And put a new ss liner in the flue you are using to seal it against leaks.

I have this crazy ideas to make the barrel out of an old pot belly stove, but haven't found one in my price range yet.

 
this is supposed to be a surprise, but it smells like a tiny ad:
Rocket Mass Heater Plans: Annex 6
https://permies.com/wiki/138231/Rocket-Mass-Heater-Plans-Annex
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