a 1000sf home will have, before furnishings, about 8500cf volume. after counting for simple furniture, maybe 7000cf. So to raise an IDEAL home of this size by 10 degrees- from 60 to 70, one would need 1260btu's.
why does the stove produce 20k or more BTUS an hour? if thats the standard, the room just went from 60 to 220f+ in one hour!
This would be the actual case if your home was surrounded by a gigantic thermos bottle which stopped ALL external heat losses. In the real world, homes lose heat to the outside world like a sieve. Granted that installing higher R rated wall and ceiling insulation, higher R rated windows and doors etc. can reduce the 'mesh size' of that sieve from large to small. But in the grand scheme of things, external heat losses for real world homes are still on the order of magnitude of a sieve !
In it's simplest form, the stove heat input versus external heat loss equation is a variant of the ever famous 'filling the bathtub while the stopper is removed from the drain' equation. Unfortunately, there are lots of additional variables such as the day to day 'height of the tub' ( temperature differential from inside of home to outside ) changing.
In the final analysis, overall wood stove efficiency is a combination of efficient combustion ( i.e. being hot enough to create secondary combustion of still flammable gases emitted by primary combustion ), and efficient transfer of the resulting heat to the home ( as opposed to much of it going up the stack in the form of very high temperature exhaust gases ).
With most stove designs, the two tend to be mutually exclusive. However, with the rocket stove design, it attempts to achieve the best of both worlds ... relying in huge thermal mass to prevent sustained high temperature combustion of the wood plus primary combustion gas byproducts from driving the surrounding temperature to uncomfortably high levels, plus relying on extensive stack heat transfer to reduce the temperature of the exhaust gases as much as is practical before they are released.
In terms of operational efficiency, every wood stove operates very inefficiently when it is first lit and coming up to temperature, as well as when it is 'throttled back' to the point where secondary combustion can no longer occur ( i.e. reduced stove temperature allowing incompletely combusted creosote vapors up the stack instead of burning them completely before they exit the stove.
Some Canadian gov't research on various wood stoves tends to show that wood stove efficiency in the absence of secondary combustion tops out around the 55% mark ... which rises to 70% or so when secondary combustion is taking place. "Trick' wood stoves such as the rocket heater, soapstone stoves, 'high tech' combustion control stoves etc. can allow the efficiency to rise to 80% ... with the caveat that these high efficiencies are only achievable once the stove's combustion chamber has reached optimal operating temperature.
Thus actually being able to take advantage of 70% to 80% combustion efficiency means that the stove needs to be sized and selected such that the BTU output capacity versus the home's need for BTU's are fairly well matched ... so that once lit the stove can continue to operate at optimal combustion temperature for a sustained period of time. This is less of a problem with a rocket stove than with commercial product stoves since everything is 'scalable' by the builder.
Personally, I went another route ... mostly so that I could do some serious cooking as well as heating.
However, one mistake I made was failing to order the ( now available ) air to water heat exchanger option ... which if installed would allow me to capture even more combustion heat for a useful purpose ( hot water supplement ) before having to throttle back or shut off the stove.
