Sauna heater size calculator
What size sauna heater do I need?
Enter your sauna's inside measurements in inches, feet or centimetres. We'll work out the heater size in kW, then show you heaters that fit.
Calculator
Find your heater size in 30 seconds
Works for cabin and barrel saunas, electric heaters and wood-burning stoves.
Enter your sauna's interior size above and we'll work out a starting point.
A guide, not a guarantee. Glass areas are typical estimates, and barrel volumes allow for the round shape. Always check the heater's own recommended room size, and ask your electrician to confirm the circuit.
How it works
The math behind your number
Here's the quick version, so you can check our working or size a heater by hand.
Measure the inside
Measure the room you sit in, not the outside of the cabin. Interior length × width × height in feet gives you cubic feet. A 6 × 7 × 7 ft room is 294 cubic feet.
Barrel sauna? We allow for the round shape, so just enter length, diameter and height.
Allow for glass and stone
Glass, tile, brick and stone soak up heat, so they count as extra room. Add 2 cubic feet for every square foot of them, glass door included.
294 cubic feet with 20 sq ft of glass becomes 334 cubic feet.
Match the kW
Allow roughly 1 kW for every 45 cubic feet. Outdoor, cold-climate or poorly insulated? Add about 25%. Between two sizes? Go up.
334 ÷ 45 = about 7.5 kW indoors, or about 9.5 kW outdoors.
Sizing chart
Sauna heater sizing chart
Use your adjusted room volume, after adding extra for glass and stone.
| Adjusted room volume (cubic feet) | Approx. m³ | Heater size |
|---|---|---|
| Up to 135 | Up to 3.8 | 3 kW |
| 136 – 202 | 3.9 – 5.7 | 3.5 – 4.5 kW |
| 203 – 270 | 5.8 – 7.6 | 5 – 6 kW |
| 271 – 337 | 7.7 – 9.5 | 6.5 – 7.5 kW |
| 338 – 405 | 9.6 – 11.5 | 8 – 9 kW |
| 406 – 540 | 11.5 – 15.3 | 9.5 – 12 kW |
| 541 – 675 | 15.3 – 19.1 | 12.5 – 15 kW |
| 676 – 900 | 19.1 – 25.5 | 15.5 – 20 kW |
For outdoor, cold-climate or poorly insulated saunas, add about 25%. Always check the heater's own recommended room size, and choose the size up if you're on the line. Bigger than 900 cubic feet? Email us and we'll help.
Questions
Heater sizing, answered
What size sauna heater do I need?
Roughly 1 kW for every 45 cubic feet of sauna, after adding 2 cubic feet for every square foot of glass, tile, brick or stone. Most saunas with a heater are outdoors, and a typical 6 × 7 × 7 ft outdoor sauna with a glass door lands at about 9 kW. The same room indoors needs about 7.5 kW. The calculator above does the math for you.
How do I measure my sauna?
Measure the inside of the room you sit in: wall to wall for length and width, and floor to ceiling for height. Don't use the outside dimensions of the cabin, since the walls and roof aren't heated space.
Why does glass make a difference?
Glass lets heat escape much faster than insulated wooden walls, and tile, brick and stone soak up heat before the room warms up. Both mean the heater has more work to do, so we count them as extra room volume.
Do I need a bigger heater for an outdoor sauna?
Usually, yes. Outdoor saunas lose heat faster, especially in colder climates, so add about 25% to the kW. Tick the outdoor box in the calculator and it does this for you.
My sauna is between two heater sizes. Which one?
Go up. A slightly larger heater copes better with glass, cold weather and a door that gets opened a lot. Just check that your sauna sits inside the heater's own recommended room range.
Does the same sizing work for wood-burning stoves?
Yes, as a starting point. Wood stoves are usually listed with a recommended room volume as well as kW, so check your sauna falls inside that range. Plan the chimney and clearances to walls and ceiling before you order.
What electrical circuit will I need?
Most home saunas run on a dedicated 240V single-phase circuit. The quick math is kW × 1000 ÷ 240 = amps, and electricians usually size the breaker about 25% above that. The calculator shows a rough figure, but your electrician makes the final call, so book them early.
Does this work for infrared saunas?
No. This calculator is for traditional saunas with a stove-style heater. Infrared saunas come with their heating panels built in and already matched to the cabin by the manufacturer.
Can you help me choose?
Always. Send your sauna's dimensions and a note on glass and location to hello@phoebe-wellness.com and we'll do the math with you.
Got your number?
Browse heaters by size, or send us your sauna's dimensions and we'll do the math with you. Call 7 days a week, 8am–6pm EST, or email or live chat any time.
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