RMH in stick built new construction

I plan on building a new house (~1500 sqft) next year. Can I heat the entire house with a RMH in the living room? It is going to be a shoe box floor plan, about 30x50 (jpg attached). It will be slab-on-grade so I could build the mass under the slab.

The other option is heat the living room and master bed room only with a "Mass wall" between the two room.

Anyone have any experience with this design?

To be efficient with a RMH in a house with that many walls I would think you would need duct work to distribute the heat.

Whether a RMH in one room will be sufficient is a matter of how much heat you need to put into the house.

How much heat you need to put into the house depends on how much heat you let OUT of the house. There are folks out there building to such extreme levels of insulation that bodies, light bulbs, and appliances are enough to keep the place warm. They're doing R60 walls and heat recovery ventilators, that kind of level. Extreme.

So clearly, if you're building like that, then you could certainly get by with one RMH for the whole house. If you don't let any heat out, then you don't need to make much heat! On the other hand, if you're cutting corners and throwing up some R11 between 2x4 studs, you're asking for trouble. When the heat's pouring out as fast as you produce it, you've got to produce a whole lot to feel it.

You also haven't told us where you are. In Fairbanks, challenging. In Austin, no big deal.


TL; DR: It depends.

If you are super-insulating the house (living in a plastic bag) then be sure you are getting enough fresh air into the house. Fresh air is useful for health.

I'd like to see a sketch where the rooms are named. I'm having some trouble identifying every room - which one is the kitchen for example? And the one in the upper right corner is a 2nd bedroom? And what is the part cut off at the top, a patio? Garage?

Anyway....

I too would suggest opening up the floor plan. Transoms are one way. But also, don't over look the idea of not running all the walls to the ceiling. Sometimes you really want to but not every room needs that.

I'd consider a re-design. Shoot for a square instead of a rectangle. Put the RMH in the center and build around it. That's how traditional homes using masonry heaters are designed, around the thermal mass of the masonry heater; a RMH is ideally the same in that regard.

Remember to insulate the concrete foundation/slab. If you do not, it becomes a giant heat sink and you can never fill it up! (Cold floors and a drain on your thermal mass is the result.)

I also do not see a southern exposure noted - maybe I just overlooked it, as I cannot see your post as I write this. Plan you eve overhangs to block the summer sun and let the lower winter sun shine inside, preferably hitting some thermal mass (and not hitting/heating it in the summer).

And as the others said - where are you at? What are the details of the construction and materials? Particular of the site and micro-climate? Etc.

I will be building in South Georgia. I plan on using R30 wall SIPS and R50 roof SIPS. It will require very little HEAT, but my concern is air distribution to the rear of the house.

The heater will be in the front right of the wall between the LR and MBR.

1) Fans are cheap.

2) I'd want a back-up heat method in those bathrooms to keep pipes from freezing, even at R30.
We used electric toe kick heaters. I think I've turned them on 1-2x per year but I'm glad to have them.

3) Can you really get a permit to do this? Let that happy news get out and people will be flocking to your area.

Sam Harris : 95% of the people who come here and are contemplating a move to their ''Forever Home", Want to Add a Rocket Mass Heater RMH, into an existing structure!

This puts you ahead of the game somewhat ! But, there is a certain hard fact to take in the RMH was designed to be a Space Heater, located at the very heart of your
home and providing you and family with one warm comfortable hang-out location.

While an 8'' system can surely heat the amount of space you want to heat, this would be in a location with an open floor plan, no interior walls, a large workshop or
garage! You can ether use supplementary heat through the rest of your house and move the pipes in the master bathroom away from the outside wall, or over heat one
area trying to warm the rest of your house !

Erica Wisner one of our Forum Moderators has just opened a New informational post on the problems of designing a system that will be mostly for part time use !

Link Below !

https://permies.com/t/41595/rocket-stoves/Rocket-mass-heaters-Texas-warm


S.I.P.s Panels : I travelled over 300 miles with an Insurance Adjuster who was called in to examine the aftermath of a Large Front-end Loader striking a house during
snow removal and much of the damage to that section of the building was actually caused by poorly executed installation of those panels! This was 3 years ago, the short
term result was A code enforcement officer declaring the structure used as a dormitory non-habitable, and a major everyone sues everyone else lawsuit !

Here is a link to ''cold weather housing Research Center, an arm of University of Alaska Fairbanks, you should look at the concrete slab work ! Also they have had many
years experience with diagnosing and preventing water build up and mold and rot conditions in super sealed structures, Their very common experience is Finding a
knowledgeable crew to make sips is one thing, finding a knowledgeable installation crew is something else and usually modifications done on the fly always turn out very
badly !

http://www.cchrc.org

Well this post turned out much more negative than was my intention ! You still have time to modify your plans ! For the Good of The Craft ! Big AL

sam hamis wrote:I will be building in South Georgia. I plan on using R30 wall SIPS and R50 roof SIPS. It will require very little HEAT, but my concern is air distribution to the rear of the house.

Wow. I grew up in Statesboro. I think you may be killing a mosquito with a gun! I just can't see needing a RMH in an extremely well-insulated house at all. Our place was a hundred years old, drafty as you've ever seen, and we got by with one of those wall-mounted propane heaters in the living room, and another in the bathroom. We just didn't need a whole ton of heat.



Have you run a heat load calculator? To see how much heat you'll need? Let me see if I can find one....

Here's one:
http://builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

That's a good one (the builditsolar heat calculator).
I think with R30 in Georgia you won't need much heat, and an 8" J-type heater would probably do it with heat to spare. I think the 6" J-type might be too small given the unpredictable winter storms the East Coast has been getting lately. Georgia sounds warm to us northerners, but you do sometimes get snow I know.

Another good general reference is http://www.huduser.org/portal/resources/UtilityModel/hdd.html the Heating Degree Days (HDD) lookup tool. Builditsolar also has an HDD map.


Just from experience:
- a 6" heater has worked for anything from 120 sq.ft. (fired twice a week) up to about 800 sq.ft. (fired each evening in the coldest months, did not heat the back room due to 2 intervening walls/poor insulation)
in the Portland, OR area (NW Oregon near the coast. Oregon is the one between Washington and California. Middle of the West Coast.) That's about 4500 HDD, and the larger building was 4" stick-frame with poor insulation, probably not more than R-19 at best.
- an 8" heater has worked for anything from 3000-5000 sq.ft. in coastal California (2300 HDD, insulation unknown) to about 1500 sq.ft. in north-central Washington or upstate NY (6000-8000 HDD/yr) with at least R-30 insulation.
The past two winters we've used about 1.3 to 1.5 cords, and as we're sometimes gone I'd play it safe and estimate we'd burn up to 2 cords if we were home all winter during a cold one in north-central WA. That's about what the 3000 to 5000 sf house in CA burned the first year they were using it, so that's a pretty doable firing schedule. They had oak/madrone, we had pine/fir/larch, and you can guesstimate the BTU/cord here:
http://www.chimneysweeponline.com/howoodbtu.htm

So that gives you a rough BTU estimate.
Very roughly: the wood's heat value is between 15 and 35 MBTU per cord (as calculated for an 80% efficient woodstove burning willow, or a 100% theoretically efficient woodstove burning Osage Orange).
So that's somewhere between 30 and 70 MBTU that a good 8" heater is putting out during a year's use, which really is probably the 6 or 7 colder months, with heavy use for 2 to 4 months.

When I've worked it out on paper, calculating the theoretical heat loss for our 840 sf home with R30 insulation using that build-it-solar site and the actual larch/fir firewood numbers, it seems like we are getting almost every BTU that's theoretically possible from the firewood we actually burned. Or, we are deluding ourselves and living happily at a somewhat lower temperature than we think. (We weighed each load of wood for weeks at a time one winter to test the theory; we are running at something under 10% moisture content when we get our wood in on time, and the exhaust temp is lower than for a woodstove, so I estimated using the middle heat value of about 7000BTU/lb. On larch, it would be about 22MBTU per cord). There's really not much heat lost to exhaust, like they estimate happens for woodstoves; you shut the stove down for at least 12 hours per day, usually more like 16 to 20 hours, and don't lose any heat to the exhaust during that time.

I think there's one other rocket mass heater I've heard about at secondhand, built in Georgia, that's an 8" system and it's heating a conventional home (probably around 2000 sq.ft.) quite nicely.

Incidentally, for anything short of a month-long muggy heat wave with no drop in night-time temperatures, you may also see some cooling benefit as well. We stopped running our stove in June, and in the Portland home we didn't have to get the fans down from the attic at all the following 2 summers that we'd needed before the stove went in. Kept the indoor temps 10 to 20 degrees cooler than outside. If you get a cool night-time or early-morning breeze, you can even chill it a bit to take up more of the daytime heat.

House Plan:
Whether this heat will reach the rooms evenly would be a question of circulation. Transoms are not a bad idea, but line-of-sight on the barrel is better. Even just a bit of that radiant heat through an open door makes a difference.

Having the heater between the LR and MBR sounds good. The ASTM E1602 standard for masonry heaters describes how to do "wing walls" to connect heaters that go through walls with any combustible framing where the standard walls take up again. Of course you can also just do a fully-masonry wall, completely non-combustible.

The main question is whether you'll need supplemental heat in those kids' BRs at the far end of the house. Can you put the kitchen stove, and/or the water heater, on that wall so the smaller BR's get some latent heat from those appliances?
Another option might be to shift things a bit. Can you run the main corridor of the house sideways, toward the right as you've currently oriented the plans? Shift those kids' BR's to just beyond the LR/Kitchen, so that one of them shares a wall with the LR and the other with the kitchen. Then you'd only have one wall between them and the heat source, and you could probably get line-of-sight on the heater's radiant bell/barrel with the smaller BR doors open. The only down side is they have to go past the kitchen to get to the bathroom, and you might end up with more midnight snacking on the way back than absolutely necessary . You can leave the bathroom as-is, swap it with the kitchen and leave a sort of breakfast nook in between, or leave it as-is and consider a WC for the other two bedrooms (just a toilet and sink).

Given that you rarely have truly evil cold snaps, maybe if the kids occasionally take a hot brick to bed when they want one, the plan might still be OK as-is. Or consider letting them camp out on the heater bench in uber-cold weather. If they're guest BR's / spare rooms, then I wouldn't worry about it; how often do you have overnight guests in a nasty storm? If one's an office, then you can also use the hot brick trick for the office-sitter's toes.

Hope that helps.

-Erica W