The Chimney Sweep Online Fireplace, Woodstove, Gas Stove and Barbecue Shop
While it might be possible to heat a large house with a small woodstove if you crank the draft control wide open and stand by to add fuel every few minutes, the preferred method is to choose a larger stove and refuel less often. The industry standard for airtights on a low draft setting is a 6-8 hour, "all night" fire, with coals left at the end of the burn to ignite a fresh load. This column shows the average output over a long burn.
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2000 - 3000
1200 - 2000
1200 - 1800
800 - 1200
Mathematicians: In order to compute the heat output of a given wood stove over a given period of time, we need to know the heat value contained in a full load of wood, the efficiency at which the woodstove delivers that heat, and the duration of the burn. We derived our sustained burn comparison figures using the formula below:
( firebox size in cu. in.) x ( 0.015 ) x ( 6200 ) x ( stove efficiency ) / ( burn time )
To get the firebox size in cubic inches, we multiplied the cubic foot measurement from the chart above by 1728.
The 0.015 is the weight of the load per cubic inch. To get this number, we used an average of the top 60 species from our firewood comparison chart, and adjusted to compensate for airspace between pieces.
The 6200 is the available BTU (heat) content per pound of fuelwood at 20% moisture content.
For stove efficiency, we use the manufacturer's published rating.
For burn time we used 6 or 8 hours, depending upon firebox size, which is an industry standard we know all our woodstoves can meet (even the little guys, if you're burning top-of-the-chart hardwoods).
Note that the average btu/hr rating derived by this formula does not reflect how the heat is actually delivered over the course of the fire. In the real world, a fresh load of wood delivers much more heat toward the beginning of the fire when the gasified resins are being consumed, then gradually delivers less and less heat as the fire proceeds through the charcoaling process. This actually works out quite well, as it takes more btu's to bring a cold house up to temperature than it does to maintain that temperature.