Investigating a strong draft blowing toward my hand-fired insert stove, I wondered how much of that draft was going to support combustion (versus, for example, the amount going to the convection blower fans, which obviously play no major or direct role in combustion).
Assume you are firing your stove somewhat above an idle—for example, you burn 24 pounds of coal in 24 hours, or one pound per hour. What volume of air is necessary, per minute, to support this combustion of one pound of coal in one hour?
(Assume you are at sea level, and air temp is 59 degrees F)
I found a link ( http://renaud.ca/wordpress/?p=49
) that went through several chemical calculations regarding combustion of coal which shed light on the issue of air flow I'd wondered about. In the example, the author uses an approximation of 70% as the percentage of carbon in coal. So, he's using bituminous coal for his estimate. Anthracite is closer to 90% carbon. He assumes—which is fair, based on other research I found—that all the carbon is converted to CO2 or CO (carbon dioxide or carbon monoxide). Thus, in a pound (454 grams) of bituminous, 317.5 g is carbon; and a pound of anthracite is 408.6 grams carbon. In his calculation with bituminous—which you can go through at the link—625 liters of carbon dioxide (at sea level barometric pressure and at about 59 degrees F) is produced by burning 1 pound of bituminous. This translates to 804 liters of carbon dioxide from burning 1 pound of anthracite. Since for every molecule (or mole, or any other amount) of CO2 produced, one molecule of O2 (oxygen) must combine with one atom of C (carbon), 804 liters of O2 are required for this combustion of one pound of anthracite. (I re-did the calculation using a molar mass of 32 for O2, as well) Since air is 21% oxygen, this means that 3829 liters of air are necessary for the combustion of one pound of anthracite. This converts to 1010 gallons of air, or about 16.8 gallons per minute. It seems hard to believe this much air is required, but I believe the calculations are correct.
Figuring out how to get this much air to the stove without having it sucked in through gaps and creating drafts, especially in already-cool rooms far removed from the stove, is a critical problem.