explaination of dry wood burns, please?

[ryjen]

I hear people tell me all the time that they "Throw on a chunk of green wood" for their overnight burn.
However, in reading the forums here, I hear that the dry wood burns longer.

What is the science behind that? Is it just the better ability to control the burn in a stove?

 

[Jags]

It comes down to the extended time that green wood requires to burn off the excess water before the wood will actually start to burn (actually the gasses if getting technical).

Can it extend burn time? Maybe. But it will be at a reduced BTU output in either case. BTU used in burning off water is BTU's that ain't heating your home.

The dangers of doing this is worthy of a whole 'nuther thread.

 

[bigbarf48]

The reason people think a green piece is burning longer is because it isn't burning well. Like jags says, a dry piece doesn't have to burn out its own moisture so it doesn't sit there and smolder and hiss. You can get long burns out of dry pieces of wood too AND for any given piece of dry wood it will produce more heat than an identical green piece

 

[Applesister]

If you have a good stove you will have control over the burn. If the stove is of poor construction it may need wood that wont dissappear too fast.
Dry wood doesnt burn slower than green. It burns more efficiently.
Water has to be converted to steam and that is where heat output is lost. And steam is bad for the whole equation. Its bad for the iron in your stove its bad for chimney flues and the air outside.
It may be tempting to burn green wood in a stove that isnt airtight.
But the solution should be to scrap the stove instead of gumming up your chimney with unburnt wood byproducts.

 

[Wood Duck]

I don't think dry wood burns longer. It burns cleaner and gives off more heat and less smoke, but it burns faster. I occasionally spend a night in a cabin at the boy scout camp and each cabin has a large, old stove. We will put the largest pieces we have in the stove before we go to sleep, and that keeps the stove warm the longest. None of the wood at camp is particularly dry, so the first few hours after we load the logs (we load with a bed of coals) the logs aren't burning much, just cooking off water. after the water is mostly gone the logs start to seriously burn, so the water actually makes the log last longer by delaying the start of serious burning of the log. The long burn is a good trade-off for less heat at camp, but I bet it makes a mess of the flue, and it isn't an efficient way to use firewood. It is also lousy for air quality.

Now that I think about it, I guess dry wood might burn longer if the dry wood enables you to set the air lower at the beginning of the burn, and that slows the burn down. With wet wood you might tend to leave the air wide open, and that could make the whole load burn faster. So, maybe dry wood does burn longer in some cases.

 

[BobUrban]

Good points made - the wood is wood so the actual "burning" of wood is relatively the same as far as time is concerned but the heat is drastically different for reasons listed above and the time of heat production is longer with wood below 20mc because you didn't wait an hour before shutting down the air. Now if you throw in some green, shut the air down and let it smolder all night you will wake up with more coals in the stove giving the impression that it is burning longer but the heat gained will be less overnight. Better to have dry rounds or squares for long burns. Go big and dry for overnights.

As I believe Dennis has mentioned many times: "Until someone comes up with a method of efficiently burning water you are just wasting energy" Not to mention the other consequences.

 

[Backwoods Savage]

I hear people tell me all the time that they "Throw on a chunk of green wood" for their overnight burn.
However, in reading the forums here, I hear that the dry wood burns longer.

What is the science behind that? Is it just the better ability to control the burn in a stove?

No science at all. Very simple, as Bob stated above. Until someone comes up with a method of efficiently burning water you are just wasting energy.

 

[Paulywalnut]

Wood duck is right. Dry wood burns with optimal efficiency, not slower. Boiling water is slower.