How big a house can they heat

We have built a well insulated hybrid straw bale house (straw bale main floor double 2x4 walls upstairs)  of about 1400 square feet in south central BC Canada. It is an open concept with as few walls as possible, good heat flow/rise to the upstairs. We are currently heating the space with a 1937 Findlay Condor wood cook stove. We have stacked functions in the cook stove but when it's -10 to -15 celsius  (14 to 5 degrees Fahrenheit) the cook stove can't get the heat much above +14 c (57 F and that takes all day (morning temp inside is about 4 C)  It needs to be fed about every half hour or the fire will go out after about 45 min to an hour..
I heard from someone else who's building that a RMH cannot heat much more than a single room but I thought they could handle much more. I have contacted Matt Walker about his rocket cook stove and heater and he said that it depends on many factors but that  1400 square feet is a lot to ask of any mass heater.
So my question is - are there any estimates of the square footage a RMH can heat i.e. houses with multiple rooms and floors ? Or is there any owner built masonry heaters that can heat entire houses ? We don't have money to hire a stone mason or get one of the pre fab masonry stoves so any direction to plans etc would be most appreciated.

I'll start with I'm not a pro RMH builder. I have built one. There are many different styles and types of heaters. Mine is just stuff we had here (fire bricks, clay, small 35g barrel etc.) As my first build I would not use this one to heat a house, but I would not hesitate and in fact will heat my house next winter with a larger one. My house is 1600 sf. and not an open concept. You should be able to heat your house no problem with a fairly inexpensive build. I would recommend building one or 9 outside to get a feel for it and figure what works for you. Its not hard to build one but its hard to get one right.

An 8" batch rocket would probably heat your house well. Check out http://batchrocket.eu/en/building#size to determine the correct size. You can even oversize and built a 10" since the dimensions are readily available. If you want more ambient heat fast, use a second metal bell that will shed fast rather than brick or cob. These stoves are built for slow release heat and contact heat like an electric blanket. I burn my j-tube rocket and my house will stay between 55-64 for multiple days with low temps outside, but the bench is 80+ and warms a person up fast with a blanket. Not for everyone for sure, but i think  keeping ambient temps above 65 is uncomfortable.

I understand the concept - I've built 4 rocket stoves for cooking on outside, but I feel to commit to this as the sole source of heating the house is a big step. I've looked at Peter van den Berg's website and it is very comprehensive about the batch style - though a little more complicated than Ernie and Erica's way of building (with building molds and casting the core with vibrating etc for Peter's style) .I'm nervous with building a 10" model in "hopes" it would heat the house. I like the idea of building test ones outside but we would never know if it will heat the house until one is built" inside the house".  I was hoping to hear from someone who actually is heating a house of a specific size and what the design of the RMH is. I'm getting a little too old to try one and if it doesn't work rip it down and try idea #2 ;)

they're more proven than ya think. There are a myriad of youtube videos of people living with them in their houses. I would hesitate to run one if I had a day job because you need to spend quality time with it every day. The times vary and I'm sure some folks have it worked out but it is the necessary truth. Once its done 2-4 hours and fully charged then your free! Really the same thing is true with my current wood stove. I cant leave for more than 6-8 hours max or shit freezes up. I would invite some qualified help on this one and get it done right. Some one here wants to go to Canada for free beer!!!

Constant 65F = Total Heat Loss + Total Heat Input (from brunt wood in RMH) being balanced
Total Heat Loss=? (this is the 1st question you will have to answer)
Total Heat Input=? (I am sure the RMH/Rocket Stove can burn a crazy amount of wood per day...outputting a ton of BTU/day)
Constant 65F = Total Heat Input (from brunt wood in RMH) -> Fast Uniform Heat Charging Rate (Air Ductwork/Liquid Radiant Heating Pipe) -> Thermal Storage -> Total Heat Loss

Given that the Rocket Stove/RMH can actually burn a crazy amount of wood outputting TONS of BTU/day, the real question is how much heat can you store in your thermal storage battery system and the rate and uniformity of heat charge and discharge.

If you could burn some wood in a rocket stove (Input) and then heat some water and do some pumped radiant floor heating (Fast and Uniform Charging) then use that to heat your earthen/cement/waterbag floor (Thermal Storage System), then you would have a nice setup.

Now quite a few factor will have to be considered.

Rate of Heat Loss due to inside and outside temperature differential
Convective Heat Loss (due to how often you open doors/windows and also infiltration, how can you improve these)
Conductive Heat Loss (due to R-Value of Insulation, how can you improve these)

Thermal storage capacity (the more mass/density/specific heat capacity the better)
Charging Rate of Thermal Storage ( (1)the more surface area/conduit/pipe/duct-work and (2)the faster the flow of heat and (3)the higher the temp difference the better)
Uniformity of Thermal Storage Charging/Discharge Rate ( The layout/size/length/width of the burn chamber and conduit)

Heat Input from Hot Water (Heat loss will just enter the house)
Heat Input from Appliance (the more KWH you use per month the more KWH that get turned into heat in the house)
Heat Input from Cooking (feel free to do alot of baking and cooking, eating out less, etc)
Heat Input from Humans ( the more active the better)
Heat Input from RMH/Heating System (the bigger the system the better)

Human Sensory-Hacks
A) Warmer Floor vs Warmer Air Temp
B) Avg Humidity vs High Humidity

Human Heat Generation and Conservation
A) Create more brown fat
B) Increase metabolic Rate
C) Being more active
D) Clothes/Blanket/Socks

Here in Europe mass heater traditionally heated very large houses in Germany Russia etc it gets pretty cold there:-)

David

Heat Lost/Heat Input = Insulation Factor(.5 to 1.8 range) * Volume(1440sqftX10ft) * Temp Difference (16F to 70F)
Heat Lost/Heat Input = 1.7* 400* 30 = 20kW

Wood Need = Heat Need / Rate = 20kW / 3.7kw per Kg of wood = 5.4kg or 12lbs
note about 1kg/2.2lbs of wood is need to raise the internal temp 1C (2F) given an outside temp of 16F and a room temp of 65F

Thermal storage
Heat Delta = 20kW
Temp Delta = 5.6667C
Rate = Heat/Temp= 20/5.667 = 3.57kw per 1C

1m3 of sand/dirt/concrete = .58kW/ 1C
Sand Volume Needed = 3.57 / .58 =6.16m3 or 218ft3 or 8cubic yard of sand/dirt/concrete

Sand Height Needed = Volume / Surface Area = 6.16 / 133.78 = 0.05m or 2inch of sand if you were to use pex/radiant floor heating with a wood heater.

Well this thing heats up my workshop, and my flat above. I haven't gone under 18C° when it was -17C° outside. Typically around 19C°/22C°. in the flat. Going from 15 to 20C° in the workshop.

http://donkey32.proboards.com/thread/1817/starting-build-220mm-rocket-double

113m² of workshop 57m² of flat approximately. And around 635 m3. Euro R7 in the walls, but not on all of them. South and east facing entrance walls are not insulated more than R1, flat gables are R2 or 3 big maximum, and R3 in the roof. All of this is euro R values.


And i usually burn this much oak in three burns a day. One morning, 2 evenings. One more in the evening if it's bellow -10C°.  

" good heat flow/rise to the upstairs."
Its not sound good at all

The convective heat is good imho, and the conductive heat in the wall is good too. Nowhere near perfect. The worse bit, is all the dust that hot air brings upstairs. It's a workshop below.

Thanks Satamax - the info you provided was great - same size space as we are planning to heat, but your design appears to require a lot of welding (I don't have a welder). Also as it will be going in the living room we hope to have something a little more aestheti ;)
Does anyone know if Ernie and Erica's designs for RMH can heat about 1400 sq feet (130 sq meters) ? Their designs seem to be simpler to build (no welding or casting a firebox) and repair/replace parts.
Thanks for any and all replies  

I'd love to hear from someone who has a Ernie and Erica design RMH currently in their house and let me know how big their house is, how happy they are with the design and how many times a day they fire it etc
Thanks again for all replies

Bryan,  my design doesn't require much welding, if at all.

You van skip metal containers if you wish. Replacing these with double skin bells. There is tons of solutions.

I would say, go for batch. Forget thé jays.



http://batchrocket.eu/en/

I constructed a double-bell masonry heater in my new home as the only source of heat.  The house is 2000 sqft, and I live in an area where the temps get very low.  I also have two cantilevers in the design where the heat cannot directly reach the exposed portions.  Simply put, a masonry heater can keep an entire house very comfortable.  You simply build the right size heater for your heating requirements, and then you insulate until the house is comfortable with that amount of heat.  This season I am adding more insulation to the attic area to help with the coldest days.  I would advise anyone who likes the idea of heating with wood to strongly consider a masonry heater; the best part is that you are not feeding a fire all day, while still heating with a sustainable resource.  I also have an integrated oven, it's my favorite way to cook everything and a total joy to have.

Bryan, our house is also really well insulated, made of straw, brick and stone.

I built a "J" 8" rocket mass heater with about 30 feet of exhaust in our extension just over six years ago. After a few tweaks it works like a dream and it really is one of the most worthwhile things I've ever built - despite all the leg pulling I had to put up with - references to "Encounters of the Third Kind" etc.

Our cleanish workshop/studio is 5x13 metres and there's a room and a bedroom directly above, making a total of 1399 square feet. That whole space is really comfortable if the temperature doesn't drop below about minus 7°c. (19°F) We have included a lot of thermal mass in the house, at strategic points : huge pillars to hold up the two floors of the extension behind the cookstove and near the RMH and the floor itself, insulated underneath with 75cms of glass bottles.

We also have a wood range which heats six radiators and 400 litres of water and I cook on it sometimes to heat the water (and usually don't light the RMH if I'm doing that) but we rarely ever need to put the radiators on except if it's really cold. Sometimes in winter, we've had a couple of weeks of just over zero F, we only used a few radiators, closed the top of the cooker down and the house is toasty warm.