KLook wrote:That is a hard one, I would think that air is the oxidation of the fuel and you can't get something for nothing so you need the same air for the same oxidation. It is just that air goes through the coal bed harder(more restrictive) and wood requires air over the fire to burn the volatiles. I think he means that he is putting more air under the fire with coal as you put non (almost) over. Coal has more carbon so it takes more air to mix with it.
If you had two burners, one oil and one propane, you would add different amounts of air to efficiently burn the fuel based on the carbon chain.
I know just enough to be dangerous. But I have burned a lot of wood and now some coal.
Me too about the dangerous statement
I think Keven is onto it. To set up my stove for coal burning the air restrictor must be removed. This increases the volume of air fed per similar opening by an estimated factor of 5. All of this is under-fire air feeds the combustion of mostly elemental carbon primarily within the deep coal bed. Wood has a higher hydrocarbon content. Wood gassifies into unburned particulates and volatile hydrocarbons that move away from the hot fuel into the space above the fuel. Overfire air and stove design (cat, non cat) influences where, when and if they fully combust.
Moisture content of the fuel is the next limiting factor. Dry wood is quoted at 12% moisture
. I've seen figures for anthracite listed in this range an lower (6-<15%). Firewood moisture content can vary from a high of 40 - 60 % for green wood (from above link) to a dry 12%. In either case, to convert a pound of liquid water to steam, it takes about 1000 btu/Lb. You can do a simple calculation to estimate how much heat (btu) from either fuel is being used to evaporate the water from a given load of fuel. The heat in the steam goes out of the flue and is a loss of heating value.
The green wood (@ 40-60% moisture) = less creosote statement is true. The trouble is the fire must burn hot and quick to maintain the wet-wood fire. High heat burns the compounds and particulates. All that moisture must be converted to steam (@ 1,000 BTU/Lb of water) to be carried out of the flue. That heat is lost to the room.