More Efficient...Big & Heavy or Thin & Light?

[Islander08]

Seems like people talk about big heavy stoves as being the most efficient. I guess this is motivated by the retained heat that allows longer refueling cycles.

I recently installed a BIS Nova fireplace, which as the name implies, is really a Built In Stove. Airtight firebox, adjustable inlet air, secondary burn. This unit is on the other end of the scale...its mostly made of lighter sheetmetal. The whole unit weighs about 225 pounds.

I'm wondering which is really more efficient. In my mind, stove efficiency is the amount of the BTU's that make it from the wood into the house. In an airtight stove, that seems to me to be every BTU that doesn't go up the chimney, either as unburned wood, or as heat lost through convection.

Doesn't all that retained heat in a heavy, high-thermal-mass stove really encourage more heat to be lost up the chimney? Seems to me the longer the firebox stays at an elevated temperature, the more time for heat to be lost to convection up the stack.

On the other hand, my BIS Nova doesn't have all that mass, and it seems the heat is more likely to travel out of the stove and into the room. It doesn't have all the retained heat of a big cast iron or soapstove stove, requiring more frequent refueling. But it appears that in terms on BTU's delivered to the living space, it might be more efficient overall. And the firebox seems like maybe it gets hotter faster so the secondary burn is more effective, helping combust unburned fuel (very little smoke).

Interested in your thoughts...

 

[begreen]

I don't think there is a hand in hand relationship between mass and efficiency. There are some very efficient designs in both lighter and heavier stoves. Mass does have better heat retention and can release the heat over a long period of time. But there is also a slower warm up time for this mass to heat up. As a counterpoint, most pellet stoves have less mass, but are generally more efficient than wood stoves.

 

[weezer4117]

this is a topic that can be argued all day, what it boils down to is personall preference. myself, i prefer a freestander over a insert. the radiant heat without the use of a fan is what sells me. my stove is a monster, takes awhile to heat it up but once it does i can easly get 70-72 temps inside 2100 sf @ 15 degrees outside. alot of heat is lost up the chimney with whatever appliance, thats why we have dampers bottom line is all units are going to put out heat, we just have to figure out the best way to transfer it into the home.

 

[Backwoods Savage]

When I see our stove top temperature between 500-600 degrees and the flue temperature at 250-350 degrees, I don't think we are losing heat up the chimney. Remember that the chimney doe require some heat in order to push the smoke and/or gasses out. A cold chimney is a worthless chimney.