Efficiency questions

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littleboss

New Member
Feb 8, 2021
8
TX
So fireplaces are 10-15% efficient. An old wood stove (non airtight) with damper in the flue is maybe 25% efficient.
So,
how much does adding a baffle increase efficiency?
how much does being airtight increase efficiency? To me it doesn't it only allows you to slow the burn down to zero if you want
how much does adding firebricks improve efficiency? I understand the bricks reflect the heat back into the fire and make it hotter thus burning more.
how much does adding secondary air intake burner tubes increase efficiency?
 

Highbeam

Minister of Fire
Dec 28, 2006
19,338
Mt. Rainier Foothills, WA
So fireplaces are 10-15% efficient. An old wood stove (non airtight) with damper in the flue is maybe 25% efficient.
So,
how much does adding a baffle increase efficiency?
how much does being airtight increase efficiency? To me it doesn't it only allows you to slow the burn down to zero if you want
how much does adding firebricks improve efficiency? I understand the bricks reflect the heat back into the fire and make it hotter thus burning more.
how much does adding secondary air intake burner tubes increase efficiency?

Since the stoves of today have all of those things and get 75% I would say that they add 50%.
 

Rearscreen

Minister of Fire
Dec 21, 2014
755
Vermont
These are good questions. I think to simply answer, smoke is unburned wood. If you can reheat the smoke to a flash point, it will burn again. That creates heat. Airtight controls an exact amount of fuel/O2 like a carburetor for maximum power. How did I do?
 
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littleboss

New Member
Feb 8, 2021
8
TX
I am building a wood stove for my shop and trying to figure out how efficient it might be over my old one. Old one only had a damper in the pipe. This one will be firebrick lined on all sides, have a baffle plate lined with fire bricks. Will also have two stainless steel secondary air intakes.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,193
central pa
I am building a wood stove for my shop and trying to figure out how efficient it might be over my old one. Old one only had a damper in the pipe. This one will be firebrick lined on all sides, have a baffle plate lined with fire bricks. Will also have two stainless steel secondary air intakes.
If done right it could increase efficiency allot. If done wrong it could do the opposite. There is allot more to building an efficient stove than just adding brick and a baffle.
 

Rearscreen

Minister of Fire
Dec 21, 2014
755
Vermont
I do know that a gentleman behind the scenes at Woodstock is a flow designer. He understands how molecules both in water and air directed can create different results. Very nuanced and way above my head. For instance, air needs to be turbulent for cats to work more efficiently. The opposite is true for aircraft at the tip of the wings and is why they are, at the very end swept up vertically. Yes you can "try" to make a wood stove more efficient as bholler pointed out but the results could create more problems.
 
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littleboss

New Member
Feb 8, 2021
8
TX
There is no way that adding firebricks would DECREASE the efficiency over on that didn't have any. Same for a baffle. A stove without a baffle has no resistance to air flow. So any baffle that slows the flow down is better than none. I realize that there is a lot to baffle design but once again, any is better than none and certainly not worse than one without a baffle.
As far as the secondary air goes. I have a piece of 1 1/4' 12guage stainless steel and I will be inserting two secondary burners. If this doesn't seem to help efficiency over my old stove then I will go ahead and add secondary air above the door like in some newer stoves that I have seen. Between primary air, and two sources for secondary to choose from I should notice some improvement. I can also add tertiary air from the rear by adding a steel box on the rear to heat the air first before letting it into the firebox. I don't have any fancy way to measure efficiency besides measure the weight of the firewood and then the weight of left over ashes and compare stove to stove.......