There are EPA wood boilers that claim over 100% efficiency.
Says more about the EPA methodology than anything else.
Just some comments, I am not saying it is not a good product but they need to review there advertising copy.
1. You can not burn wood without smoke, not even the most advanced lambada controlled German Boilers, it is just not possible.
2. I get worried when I see mention of sq ft as a heating load, Medieval Cathedral or Passivhaus? 10btu's per sq ft suggests nearer the latter.
3. I used to handle Intertek's Insurance programme, they would have tested it in accordance with their clients request to whatever standards specified. Now I am not saying it is the case here, but I remember reading that one OWB manufacturer used dimensional lumber for EPA testing. I am going to guess that this is not a common fuel for OWB's.
4. 10 hour burns with high efficiency, the Intertek results were on shorter burns, I would be interested to see how output varied with time, how well the controls managed variances in burn.
Just one question, something I had suppose but never looked into, I thought you needed 2000F for good gassification rather than 1000F?
Excellent Questions
1) EPA current methodology has nothing to do with efficiencies. It's all about emmissions. This will change in the next iteration probably in the next year or so.
2) I dont know about that boiler maker's claim to efficiencies. Depends what he's measuring. Heat exchange ability? Combustion? other parameters? Buyer beware if they do not provide what they are measuring to and to what standards.
3) It is possible to attain close to 100% efficiencies (LHV). Some European boiler MFG are close to it. But in order to do so they have to power vent it since there is not enough heat loss for natural draft. Plus they need complex electronics and stack dehumidifier in order to work properly. They are also very expensive. So your overall efficiencies and ROI is not really what it should be. If we are talking about efficiencies in terms of how much heat is retained in the house there are 3 different tests to measure this: Stack Loss, Low-Heating Value (LHV), High Heating Value (HHV). Wood stoves uses primarily Stack loss method, while furnaces and boilers uses LHV & HHV. We state both in our literature. Also keep in mind that in these 2 last methodology 'jacket loss' is not included. It means if a furnace is 80% efficient LHV it probably is even more since there is always heat radiating from the furnace itself (not in the exchanger). And since this heat stays in the house... Bonus!
4) It is possible to burn wood appliances without *visible* smoke. The current EPA emission standard for wood stoves is no more than 7.6 gr/hr. This is accomplished over 4 burn cycle. Most of that smoke is on start up. Once your firebox is up to temp you will not see any smoke. The new EPA standard for wood stove will likely be 4.5 gr/hr while for furnaces and boilers it will likely be 4.5 gr/Megajoule (gr/million BTU).
5) You are right... Sq ft specifications for wood stove is a rule of thumb at best since there are too many variables to really provide a good indication. For furnaces and boilers it is a better indicator since its a forced air unit (or Hydro unit).
6) You are also correct. Current EPA testing for wood stoves requires cribbed dimensional BC Fir. Remember they are measuring emissions not efficiencies or BTU output. The new EPA legislation will hopefully change that.
7) Lab tests for certifications are done with a minimum of 4 tests which are averaged. This is done under ideal conditions. Therefore Lab burn times are not indicative of the 'real' world. We've obtained 19Hrs burn time for the Max Caddy in the lab. However, we state 8-12 Hrs in our marketing material. Again too many variables to define what burn time really is.
8) The OP title is a misnomer. Neither the Kuuma or the PSG Caddy lines are gasification furnaces.
The problem with wood or rather the beauty of it is it's a non-standard fuel... Unlike gas or oil, each load, each cycle, each log is different. Therefore the difficulty to establish consumer specs such as burn time, sq ft etc...
Hope this helps.