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Simple method to Calculate how many or what size of RMS needed?

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Hi, I am new and excited but ready to get my hands dirty and try this out.

I am designing my own home and settled on the idea of a Rocket Mass Stove to cook on and feed the underfloor firebrick flues of each of two 3x3sqm sleeping rooms, one 3x3sqm shower/toilet room and one 4x4sqm sleeping room.The rooms will be raised from the cooking area as with most ondol/hypocaust systems but with the stove situated in the centre of the square shaped floorplan (the sleeping rooms and shower/toilet room form two sides of the build - North and East) (the living space will be a square shape using the South and West sides of the house).

I have even considered that because I placed the shower/toilet room at the South East corner that itself my have a small ondol/RMS of it's own, separate to the two 3x3sqm sleep rooms and the one 4x4sqm sleep room at the North East corner of the house.

I am concerned with building an ondol/RMS that is not large enough to heat all the sleeprooms for the colder nights, and certainly didn't want to face having to dismantle the whole thing,and start over; is this the way everyone else has done it, or do you all kind of know what size of burner will heat a certain size of floor space?

Any helpful info is greatly appreciated.

I did read the FAQ's but could not find a way to calculate the plan.

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Location: Upstate NY, zone 5
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There are so many variables that it is hardly possible to perform useful calculations. In general, for a fairly well insulated medium sized house in a climate with real winters but not brutally cold, an 8"/20cm system will usually work. Much of the published experience is with US building practices, so Swiss practices may be different enough that this is not accurate. It is not easy to make a RMH that is too big for a given building and climate; you simply fire it less often if your heating needs are lower, and the mass slowly radiates the heat.

There are rules of thumb for the size of bells that a given combustion unit can support to heat effectively without wasting heat up the chimney or taking so much that the draft suffers. Underfloor hypocaust or ondol arrangements may behave differently from a masonry-enclosed bell, I couldn't say.

There are several members here from Europe who may be able to give advice based more on your building and climate conditions. There are a number of European members at the rocket mass heater forum http://donkey32.proboards.com who could give detailed advice.
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