Conflicting views: more air=more/less heat?

[martel]

working on getting a hotter burn. i ran across conflicting views between the inof on hearth.com and regency's site:

regency claims:

Master the art of draft control. By controlling the flow of air into the firebox, you can control the burn rate of your fire. The less air, the slower it burns, the longer the wood lasts, and the more heat you get. Always keep the air shutter completely open when starting your fire, letting the logs catch before choking off the air.

while an article around here tells me:

#3 - Close the door, open the air inlet to get the wood burning well. Adjust the air inlet (less air) when you are comfortable with the heat output. More air=more heat and a shorter burn time. Less air=less heat and a longer burn

what's the call on this?

 

[KarlP]

Its a trade off. "Too much" air means the fire burns hotter, but more air flow also means more of the heat goes up the chimney. The "right amount" of air flow means the fire burns a little cooler, but far less heat goes up the chimney so you can get more heat into the house this way. "Too little" air and the fire smolders and much of the smoke goes unburnt and goes up the chimney.

 

[MountainStoveGuy]

I think #3 says it all. I dont really see a conflict of information.

 

[martel]

I think #3 says it all. I dont really see a conflict of information.

MSG-

aren't these two reports absolutely conflicting? it seems regency says "less air=more heat" the hearth.com article says "more air=more heat" I certainly trust your opinion, but you need to straighten me out regarding how these are not opposites.

the regency link:
http://www.regency-fire.com/Tips/Wood.php

the hearth link:
https://www.hearth.com/what/tending.html

and what is your view on heat escaping up the flue when it is cranked open?

 

[webbie]

aren't these two reports absolutely conflicting? it seems regency says "less air=more heat" the hearth.com article says "more air=more heat" I certainly trust your opinion, but you need to straighten me out regarding how these are not opposites.

the regency link:
http://www.regency-fire.com/Tips/Wood.php

the hearth link:
https://www.hearth.com/what/tending.html

and what is your view on heat escaping up the flue when it is cranked open?

It depends on the stove as well as the chimney and wood - BUT, given a stove with a decent baffle and smoke path, as well as some stovepipe in the room, more air =more heat and shorter burn.

Actually, it's really a "stage" thing which you will find mentioned in other articles. The basic rule applies to when the wood is first added and is burning most of the gases. When the wood has turned to coals (carbon), a longer burn and possibly more heat can be obtained by - as Regency says - "mastering the art of the damper.

This can usually be actually felt by the user- especially in older stoves. I remember closing a stack damper in my old funky wood burners in WV and TN, and you would immediately feel the radiant heat increase greatly.

But, given a newer and efficient stove, it can generally be said that more air equals higher output and a shorter burn.

 

[martel]

Thanks guys- I was sort of hoping this was part of my problem- burning at full tilt with little heat output... keep trying I guess. waiting for a call back from the installer/

 

[martel]

I think both approaches that you cited treat the subject simplisticly.

say more brave helios!

 

[MountainStoveGuy]

A piece of wood has X amount of BTU stored in its woody fibers. That amount doenst change from stove to stove. If you burn that piece of wood up in lets say a hour, then you have released all its btu's in a hour. If it takes three hours then you have released the same amount of btu's over three hours, only slower and not as hot. But the same energy has been released. Some would argue that if you burn youf firebox full of wood up quickly, you have wasted some heat and your room is too warm. If you slow it down, its possible to heat your room to a more comfortable temp and keep it there over a long period of time. There is still X amount of energy in that firebox, and its up to you how fast you want to release it.

 

[martel]

A piece of wood has X amount of BTU stored in its woody fibers. That amount doenst change from stove to stove. If you burn that piece of wood up in lets say a hour, then you have released all its btu's in a hour. If it takes three hours then you have released the same amount of btu's over three hours, only slower and not as hot. But the same energy has been released. Some would argue that if you burn youf firebox full of wood up quickly, you have wasted some heat and your room is too warm. If you slow it down, its possible to heat your room to a more comfortable temp and keep it there over a long period of time. There is still X amount of energy in that firebox, and its up to you how fast you want to release it.

Simple and logical- now what about heat up the chimney? anything to it or is it not significant enough to make a difference with a new and very efficient stove?

 

[MountainStoveGuy]

I think secondary combustion will take place in the life cycle of the load of wood being burned at some point during the burn, weither its a fast burn or a slow one. When your not combusting completly, then your wasting "fuel" up the chimnney. One thing i havent thought about before, is smoke btu's factored in the dry wood btu's? and i suspect its not, so i wonder if there is a btu per cubic foot of smoke measument?

 

[Sandor]

I think by slowing down the air intake, the hot gases have time to complete combustion within the firebox, instead of burning in the chimney.

With my two Regency's, backing down the air intake created a "firey cloud" in the roof of the firebox, lotsa heat, and no smoke.

Caveat with Regency, if turned it too far down, or the wood started to burn out, secondary combustion would not occur then ya start the process over....

On my Woodstock, it burns hotter while burning smaller loads with the air turned down to about 3/4, rather than wide open.

Did any of that make sense?

 

[MountainStoveGuy]

I would agree with sandor. There is a sweet spot on ever stove, a point of diminishing return if you will. You burn it to slow and cool you dont burn the gasses efficiently. You burn it to hot and fast you loose some of the gasses up the flue. On my stove, i dont get smoke no matter where i burn it as long as i dont damp it down when the logs are still catching.

 

[Mo Heat]

... One thing i havent thought about before, is smoke btu's factored in the dry wood btu's? and i suspect its not, so i wonder if there is a btu per cubic foot of smoke measument?

It's all included. Smoke and carbon.

 

[rudysmallfry]

I like this thread. I've been stuck home for the past month with a bad leg bored out of my mind. Most of the time, I sit and watch my fire burn. I've done LOTS of experiments. I agree with the sweet spot theory. Every setup has that maximum heat setting. With my Heritage, when I reload I let the wood burn strong for about 10 minutes. Once I turn the air down to about 1/4, my stack temp quickly shoots up about 50 degrees, and my soapstone gains at least 100 in a very short time. It seems to radiate it better as well. With anymore air, it's more burning, less heat. With the air off, the heat isn't as intense.

 

[webbie]

Simple and logical- now what about heat up the chimney? anything to it or is it not significant enough to make a difference with a new and very efficient stove?

This can be a BIG DEAL in a fireplace insert! We've had many discussions over the years regarding the advantage of stoves on the hearth or inserts without panels, etc.

We only have to look at the mechanics of inserts to see that a LOT of the heat is thrown to the top and rear plates of the unit and up the chimney. Sure, a blower gets some of this out - but "some" is the operative word.

Given this, the forumula we have been discussing is not valid. In such a situation, a high fire might create output, but a lot of that output might not go into the room. So a smaller or medium fire damped down might be substantially more efficient in such an insert.

 

[BrotherBart]

I like this thread. I've been stuck home for the past month with a bad leg bored out of my mind. Most of the time, I sit and watch my fire burn. I've done LOTS of experiments. I agree with the sweet spot theory. Every setup has that maximum heat setting. With my Heritage, when I reload I let the wood burn strong for about 10 minutes. Once I turn the air down to about 1/4, my stack temp quickly shoots up about 50 degrees, and my soapstone gains at least 100 in a very short time. It seems to radiate it better as well. With anymore air, it's more burning, less heat. With the air off, the heat isn't as intense.

Every wood burner since cave man times has gone to his grave "just knowing that I could have gotten more heat and longer burns out of that wood".

The pellet guys don't seem to worry about it. Of course the cave men only had rabbit pellets to work with. Or dinosaur pellets. Whoa!

 

[martel]

Simple and logical- now what about heat up the chimney? anything to it or is it not significant enough to make a difference with a new and very efficient stove?

This can be a BIG DEAL in a fireplace insert! We've had many discussions over the years regarding the advantage of stoves on the hearth or inserts without panels, etc.

We only have to look at the mechanics of inserts to see that a LOT of the heat is thrown to the top and rear plates of the unit and up the chimney. Sure, a blower gets some of this out - but "some" is the operative word.

Given this, the forumula we have been discussing is not valid. In such a situation, a high fire might create output, but a lot of that output might not go into the room. So a smaller or medium fire damped down might be substantially more efficient in such an insert.

I will find the sweet spot this week... (insert junior high humor here)