How this calculator works
The usual rule of thumb is to multiply the floor area you want to heat by the BTU per hour a square foot needs in your climate: about 20 in a mild climate, 30 in a moderate one, 40 in a cool one and 50 in a cold one, for an average house with an 8 ft ceiling. We then scale it by the ceiling height (taller rooms hold more air to heat) and by how well the space is insulated.
Worked example: a 40 × 25 ft space (1,000 ft²) in a cool climate with average insulation and an 8 ft ceiling needs 1,000 × 40 = 40,000 BTU per hour (11.7 kW). With 10 ft ceilings it is 50,000 BTU/h, and with poor insulation 50,000 BTU/h. A small 20 × 15 ft room in a mild climate needs only 6,000 BTU/h.
Stove size by floor area and climate
BTU per hour for an 8 ft ceiling and average insulation. Multiply by 0.8 for a well-insulated space and by 1.25 for a poor one.
| Area | Mild (20) | Moderate (30) | Cool (40) | Cold (50) |
|---|---|---|---|---|
| 400 ft² | 8,000 | 12,000 | 16,000 | 20,000 |
| 500 ft² | 10,000 | 15,000 | 20,000 | 25,000 |
| 600 ft² | 12,000 | 18,000 | 24,000 | 30,000 |
| 1,000 ft² | 20,000 | 30,000 | 40,000 | 50,000 |
| 1,600 ft² | 32,000 | 48,000 | 64,000 | 80,000 |
| 2,000 ft² | 40,000 | 60,000 | 80,000 | 100,000 |
Tips before you buy
- A stove heats the room it is in. Heat reaches other rooms through open doorways, so a stove in an open-plan living area is the most effective, and bedrooms down a hall stay cooler.
- Do not buy the biggest stove. A stove that is too big is run on a low, smoldering fire that makes smoke and creosote and blackens the glass. A stove a little too small can be run hot and clean.
- Fix drafts and add attic insulation first: a better sealed house needs a smaller stove, and the stove is easier to run.
- A fan or ceiling fan on low moves the warm air from the stove room to the others. Use dry, seasoned firewood (below 20% moisture).
- The stove needs the right clearances to walls, a non-combustible hearth, a chimney or flue sized for it, and often a permit and inspection. Fit a carbon monoxide alarm and have the chimney swept every year.
Tools & materials for this project
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Frequently asked questions
What size wood stove do I need?
Multiply the floor area by 20 to 50 BTU per hour per square foot, depending on climate. A 1,000 ft² space in a cool climate needs about 40,000 BTU/h, so shop for a stove rated for roughly 48,000 BTU/h.
How many BTU per square foot for a wood stove?
About 20 in a mild climate, 30 in a moderate one, 40 in a cool one and 50 in a cold one, for a typical house. Add about 25% for a poorly insulated space and take off about 20% for a well-insulated one.
What size wood stove for 1,000 square feet?
About 30,000 BTU/h in a moderate climate and 40,000 BTU/h in a cool one, with an 8 ft ceiling and average insulation.
Is it bad to have a wood stove that is too big?
Yes. An oversized stove is run on a low, smoldering fire to keep the room from overheating, which gives incomplete combustion, smoke and creosote in the chimney. A properly sized stove can burn hot and clean.
Does the stove heat the whole house?
It heats the room it is in best. Heat spreads through open doorways and with a fan, but a closed-off room or an upstairs bedroom stays cooler. Size the stove for the area the heat can reach.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.