What Size Wood Stove Do I Need? BTU by Area and Climate
The usual rule is to multiply the floor area to be heated by 20 to 50 BTU per hour per square foot, depending on your climate. A 40 × 25 ft space (1,000 ft²) in a cool climate needs about 40,000 BTU/h (11.7 kW), so a stove rated near 48,000 BTU/h is a good match. The wood stove size calculator also adjusts for ceiling height and insulation.
Part of the project planners: Planning heating, cooling and ventilation and Getting the house ready for winter.
Stove size by area
An 8 ft ceiling, a cool climate (40 BTU per ft²) and average insulation. The last column adds about 20% to the need.
| Space | Area | BTU/h needed | Stove rating to look for (BTU/h) |
|---|---|---|---|
| 15 × 12 ft | 180 ft² | 7,200 | 8,640 |
| 20 × 15 ft | 300 ft² | 12,000 | 14,400 |
| 25 × 20 ft | 500 ft² | 20,000 | 24,000 |
| 30 × 20 ft | 600 ft² | 24,000 | 28,800 |
| 40 × 25 ft | 1,000 ft² | 40,000 | 48,000 |
| 40 × 40 ft | 1,600 ft² | 64,000 | 76,800 |
By climate
The same 1,000 ft² space, an 8 ft ceiling and average insulation:
| Climate | BTU per ft² | Needed | In kW |
|---|---|---|---|
| Mild | 20 | 20,000 BTU/h | 5.9 kW |
| Moderate | 30 | 30,000 BTU/h | 8.8 kW |
| Cool | 40 | 40,000 BTU/h | 11.7 kW |
| Cold | 50 | 50,000 BTU/h | 14.7 kW |
By insulation
A cool climate, the same space:
| Insulation and windows | Factor | Needed |
|---|---|---|
| Good | 0.8 | 32,000 BTU/h |
| Average | 1 | 40,000 BTU/h |
| Poor | 1.25 | 50,000 BTU/h |
These BTU per square foot figures are the rule of thumb used by stove makers and dealers: they are not a heat-loss calculation, so use them to choose between sizes, not to size a furnace.
Before you buy
- Choose an EPA-certified stove, and compare its heating output in BTU per hour, not the "area it heats" on the brochure.
- The stove needs clearances to walls and ceilings, a non-combustible hearth and a chimney or flue that suits it. Many places require a permit and an inspection.
- Burn dry, seasoned firewood below 20% moisture, and see the firewood calculator for the cords you will need.
- Fit a carbon monoxide alarm and a smoke alarm in the room, and have the chimney swept every year.
- Seal drafts and add attic insulation first, since a tighter house needs a smaller stove.
See also the furnace size calculator and the heating cost comparison. Estimates only: follow the maker and your local code.
Frequently asked questions
What size wood stove do I need?
Multiply the floor area by 20 to 50 BTU per hour per square foot, by climate. A 1,000 ft² space in a cool climate needs about 40,000 BTU/h, so look 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 an average house with an 8 ft ceiling.
Can a wood stove be too big?
Yes. An oversized stove is run on a low, smoldering fire to stop the room overheating, which makes smoke and creosote and blackens the glass. A stove sized to the space can burn hot and clean.
Will one stove heat my whole house?
It heats the room it is in best. Open plans and doorways let the heat spread, and a fan helps, but rooms with closed doors, and upstairs rooms, stay cooler.
Is the listed heating area on the stove reliable?
Only as a rough guide. It assumes a typical house in a typical climate. Use the BTU output and your own area, climate and insulation.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.