oldspark said:
If the efficiently rating of the stoves are pretty much the same cat vs non cat and the fire boxes the same size would not the consumption of the wood for the heat given be the same or so close to call?
They aren't the same. Look at Woodstock, for example. All four of their models are using the EPA default of 72% efficiency for a cat stove. It is apparent to me that these were not numbers generated from test data or they wouldn't all be identical. Perhaps these stoves are actually higher in efficiency than the advertised figures? In contrast, the EPA default efficiency for a non-cat (secondary combustion) stove is only 63%.
It's hard to deny that cat stoves are, in general, more efficient. I've always like the idea behind them, but fell prey to the horror stories. Large industrial manufacturers often use catalysts to increase their yields (i.e. increased efficiency). The same reactions could be forced to completion using heat, pressure, continuous product removal, etc., but the bottom line is that the appropriate catalyst puts the molecules into a better configuration for reactions to occur, so lower energies of activation are needed. That's why cat stoves don't need to achieve 1100ºF to burn off the gases. If the reaction can proceed at 500º instead, there is a much greater chance that more molecules will combine with the oxygen molecules need for complete combustion.
There are other reasons for reduced wood consumption as well. Burn efficiency is only a part of the equation. Heat transfer efficiency is the part we are all concerned with. The Woodstock stoves have no insulating materials in them. You have to use more energy to get all that stone up to temp, but in the end nothing is lost. The heat comes out steadily and evenly for a longer period of time. Compare that with my VC stove. That thing just blasts the heat out, but that raises the temperature of the room too high. The excess heat is transferred to the outdoors through the walls of my home more rapidly because of this. Then the fire dies down and the stove cools off and I am forced to load it again to keep it warm in here. In effect, I am forced to over-stoke my stove, and this has zero to do with it's actual burn efficiency (which I am convinced is a lot higher in my stove than in many of the old dragons). But Woodstock stoves (and other cats, I'm sure) can maintain their high efficiency at very low burn rates. The Fireview can put out as little as 10,000 BTU/hr and still burn clean. I don't think my stove can do that and still stay lit. I think I'm wasting a lot of wood just keeping it burning clean.
I don't think it has so much to do with burn efficiency (EPA rating) as it has to do with the fact that a properly sized cat stove can give off just enough heat to do the job over a much longer period of time. If you still feel warm, you won't be refilling your stove as often. Less refills means less wood used. Add in the heat storage ability of 500 pounds of soapstone like in the Woodstock stoves and I think you have a winner.
I have been thinking long and hard about the Woodstock stoves since I visited the factory, and I am seriously thinking of trying one out in my basement. The time is
now as far as their offers go, but I'm kinda broke right now so I may have to wait. Still, it might be worth it for me to buy one through their financing (9.9%) plan, so persuade me to go into debt, I'll love you for it.