"Cat stoves do very well with smoldering fires."

S&W, here is a table that may be of help to you.



Interesting to see the effect of air in the system. Convection transfer rises to about 40% of the total energy at a peak temp of 150-200ºF, then drops as the temp of the radiating surface rises beyond that. In a vacuum, all of the heat would be transferred by radiation alone.

Here are a few charts that show the same info, plus some other interesting stuff.

http://www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html

so what happens if a fan increases the convection & decreases the radiation temp?

The same amount of heat will be transferred as long as the same amount of heat is being generated inside the firebox. It has to leave through the flue or through the stove walls, or the internal temp has to rise. You can get more heat transferred by using a fan and increasing the draft, but you had better watch that if you are going to extremes. You just might cook the inside of your stove.

So, a given amount of material can transfer a given amount of heat and the rest goes up the pipe right? What I have found is that if I have the tstat set at the same place on the BK, so firebox temp the same, with the blowers on my burn time decreases by about one third over no blowers. What I have wondered is how much of that 50% increase in burn rate went into the house and how much went up the pipe. It would seem that I need a thermometer in the double wall stove pipe to answer that as it is always cool to the touch.

The big question is did BK succeed in creating a large stove that can burn both high and low equally efficiently or is there a trade-off there I should consider when setting up the burn. Or, not worry about it and pump as much heat into the house as needed when needed to keep the family happy.

Todd, indeed Wendell sent his back but there also was another fellow who had only a very few posts on here. He never did come back on but his posts led me to believe he would be sending the stove back. The poor fellow just did not have a good setup for any type of stove to do what he wanted it to do. I just do not remember when the post was made or who made it. Was it last winter or the winter before? My memory bank is overdrawn at present.

I never think in terms of absolutes when it comes to engineered products. This theoretical stuff is just for sitting around our digital campfire here discussing things. There is much that can't be directly measured and accounted for in complex systems like wood stoves. These are the things that give real engineers fits, and the reason why the perfect stove hasn't been invented yet. Modeling, prototyping, testing, analyzing, rebuilding, testing some more, analyzing some more, etc. All part of the iterative design process. Then there is the matter of what to do with the feed back from real world users who can't get the products to work as designed, or can't maintain them knowledgeably, etc.

That said, if the BK does in fact accurately monitor and control the actual internal firebox temp, then I believe that running the blowers will primarily push heat into the room and not up the flue. The blowers will cool off the outside of the stove, and this will mean that heat from the firebox will be drawn faster from the fire because of the greater temperature differential. The thermostat should sense this and give the stove more air to maintain the proper temp for clean combustion. I think the net effect would be to pull more heat from the fire into the stove walls and then allow radiation and convection to move it away and through the room.

However, even if the flue temps remain the same, in order to get more heat you will need a larger volume of air. That means more air at that same temp will have to pass through the stove and go up the flue. I don't see how you'd end up with a net gain in efficiency. There could be even be a small loss in efficiency (doubt it, though), but I don't feel it would be significant enough to avoid using the blowers. If you are getting more heat when you need it, go with option "B" and make the family happy. That's what it's all about, eh?

Yeah, that is definitely what its all about. From the crude experiment of watching what the stove does when you turn the blowers on or off, I think the BK does a pretty good job monitoring the firebox temp. It adjusts within 30-40 seconds.