What is more efficient (uses less wood)?

[velvetfoot]

A small stove/insert working at capacity more times than not, or a larger unit?
Any empirical data on this anywhere?

 

[begreen]

Tom Oyen might want to chime in on this one. I remember reading about the early epa tests on his website. They found that even an older stove, if burned correctly, put out lower emissions once it was running hot. So empirically I would think that a smaller stove running continuously at peak efficiency would be much cleaner than an oversized stove that has to be throttled back and burn short fires a large part of the season. The dirty part is in the startup and/or running too cool.

 

[thechimneysweep]

This is the sort of question that makes me cringe, because there are so many variables that need to be considered, and so many possible arguments that could be made against any hastily written response, that there can really be no hard-and-fast answer.

That said, here's my hastily written, hard-and-fast answer:

Let's say you need an average of 40,000 btu/hr to heat your house. You could produce that amount of heat by burning a 28 lb. load in a size-small Pacific Vista at a fairly open setting, and reload another 28 lbs. of wood every 4 hours or so. You could also produce that amount of heat by burning a 60 lb. load in the larger Pacific Summit turned to its lowest setting, and reload it every 8 hours or so. Either way, you'd be burning the same amount of wood to heat the same area for the same period of time.

 

[Corie]

I think you're better off with the smaller stove and here's why: Larger stoves are not tested with small loads for certification testing; the fuel load is a function of firebox volume only and often times the low burn air properties are designed for the EPA sized load. I've noticed that larger (standard secondary combustion in firebox top) firebox woodstoves generally do not perform wonderfully with small partial loads of wood. This isn't a hard, fast rule, but just something I've noticed, which I think is a byproduct of the testing procedure.

 

[thechimneysweep]

Hey Corie,

I read the original question as being about the draft control setting, not the size of the fuel load. If, as in my example above, you need 40,000 btu/hr to heat your house, I'll agree that putting a small load in a big stove isn't going to get you there. I was comparing two fully loaded stoves, and suggesting a fully loaded big stove with the draft control adjusted down for a long, low burn would burn about the same amount of fuel as a fully loaded firebox half the size burning wide open and being reloaded twice as often.

 

[begreen]

This is just an empirical observation on today's wood burning. It's not super cold out. I thought if I filled the stove to the gills the house would get too hot, so I started out burning just two splits at a time. I had a good fire, but the stove never kicked into high-gear secondary burn. It stayed at about 350-400 degrees. This evening I filled the stove and it took off nicely. In 30 minutes it was at 500 degrees and when dampered down had strong secondaries for a couple hours (softwood maple). So it seems to me that burning smaller fires in a big stove is not as clean as a long intense burn. The question is, how does one do that in an oversized stove during the shoulder seasons without cooking oneself out of the house? (Besides opening a window which is inefficient.)