Home Calculator
Stove sizing and fuel cost Built on tested output
Two calculators: one checks each stove’s EPA-tested maximum against the heat your space needs, the other turns your local cord or ton price into a season cost using the stove’s HHV efficiency.
Both calculators use the certified figures, not the headline ones. The sizing check compares your heat load with each stove’s EPA-tested maximum output, which is what a stove sustains on a full test load. The fuel calculator uses each stove’s EPA HHV efficiency, the strict basis, so the cords or tons it shows lean toward the high side.
Heating Area Calculator
Enter the area you want the stove to carry and a heat load per square foot. We multiply them and check each stove's EPA-tested maximum output against the result.
Heat needed: 52,500 BTU/hr
| Stove | EPA-tested max | Covers it? | Advertised max | Advertised area |
|---|---|---|---|---|
| Turn on JavaScript to use the calculator. The stove table lists every figure. | ||||
35 BTU/hr per sq ft is the sizing rule in Castle's Serenity manual for homes built after 1982 (Castle manual). Older, leakier or colder homes need more; tight new builds need less. A real heat-loss calculation beats any rule of thumb. EPA output from the EPA Certified Wood Heater Database, checked 2026-10-21.
Fuel Use and Cost Calculator
Enter the heat your home uses in a season and your local fuel prices. We divide by the fuel's gross heat content and the stove's EPA efficiency to get cords or tons, then multiply by your price.
| Fuel | Heat delivered per unit | Needed per season | Cost per million BTU delivered | Season cost |
|---|---|---|---|---|
| Turn on JavaScript to use the calculator. | ||||
Gross heat content from the USDA Forest Products Laboratory Fuel Value Calculator (updated 01/24): seasoned firewood at 20% moisture 20 million BTU per cord, premium pellets 16.4 million BTU per ton. The same source says an average home typically uses 50 to 150 million BTU in a heating season. Cost per million BTU follows the method in EIA's fuel comparison FAQ. Wood species, moisture and how you run the stove all move the real number. We don't supply fuel prices because they vary too much by region; use a quote from your supplier.
How to Use the Numbers
- “How many sq ft will it heat?” is the most common question in r/woodstoving and r/PelletStoveTalk, and the honest answer is “it depends on the house.” A tight, well-insulated house needs far less heat per square foot than a drafty farmhouse in the same town. Start with Castle’s 35 BTU/hr rule if you don’t know, then adjust it against what your current heating system actually burns in a cold month.
- Pick on the tested maximum, not the advertised one. A stove that only covers your load at its advertised maximum will be running flat out, burning through wood and reloading often. A stove whose tested range puts your normal winter load in the middle, rather than at the top, is the one that runs clean and holds a long burn.
- Fuel cost per million BTU is the fairest way to compare a cord of wood with a ton of pellets or a gallon of propane. The formula is price ÷ (gross heat per unit × efficiency). To compare with your current furnace, use EIA’s heating fuel comparison calculator with the same season heat figure.
- Firewood varies most. USDA’s 20 million BTU per cord assumes seasoned wood at 20% moisture. Softwoods have less energy per cord than oak or hickory, and wet wood loses a large share to boiling off water. A cheap cord that “seems barely seasoned” is rarely a bargain.
See the stove comparison for each stove’s full figures, or stove BTU ratings explained for why advertised and tested output differ.