Sauna Heater Size Calculator
Enter your sauna's inside dimensions, plus any glass or bare masonry, and the calculator shows the electric heater size that fits, how many amps it draws, and heaters we carry in that size. It uses Harvia's published room ratings and Harvia's own rule for glass, masonry and log walls.
Sauna Heater Size Calculator
Enter your sauna's inside dimensions to see which heater size fits.
Your recommended heater size will appear here as you enter your measurements.
Room ranges are Harvia's published ratings (Kip 3 to 8 kW, Cilindro and Virta 9 to 10.5 kW). Adjustments follow Harvia's rule: add 1.2 m³ per m² of glass or masonry (about 3.9 cu. ft. per sq. ft.) and multiply by 1.5 for solid log walls. Confirm the range for your specific heater on its product page. A licensed electrician should confirm breaker and wire size.
How the Calculator Sizes Your Heater
- Room volume. Length x width x height of the inside of the sauna, in feet. For a barrel, choose Barrel and enter the inside diameter and the length of the heated room.
- Heat-loss adjustment. Glass, tile, stone and concrete absorb heat, so each square foot adds about 3.9 cubic feet (Harvia's 1.2 m³ per m²). Solid log walls multiply the whole volume by 1.5.
- Match to a rated range. The calculator picks the smallest heater whose range covers your adjusted size, and steps up one size only when you're near the top of that range. It never recommends going past a heater's rating.
Sauna Heater Sizes at a Glance
| Heater Size | Sauna Size (cu. ft.) | Amps at 240V | Shop |
|---|---|---|---|
| 3 kW | Up to 130 | 12.5 A | 3 kW heaters |
| 4.5 kW | 100 to 210 | 18.8 A | 4.5 kW heaters |
| 6 kW | 170 to 300 | 25 A | 6 kW heaters |
| 8 kW | 250 to 425 | 33.3 A | 8 kW heaters |
| 9 kW | Up to about 500 | 37.5 A | 9 kW heaters |
| 10.5 kW | 400 to 636 | 43.8 A | All electric heaters |
Ranges are Harvia's ratings for the Kip (3 to 8 kW) and Cilindro and Virta (9 and 10.5 kW). Other brands differ slightly; check the product page for your heater.
Why the Calculator Won't Tell You to Go Bigger
The most common sizing mistake we see is buying a heater that's too big to make sure the sauna gets hot. It doesn't work: every heater's thermostat stops at the same maximum temperature, a bigger heater only heats slightly faster, and the extra output dries out and scorches the wood closest to it. A customer outside Santa Fe, New Mexico, put an 8 kW heater in a sauna sized for 4.5 to 6 kW, with a bench close to the heater. The sauna got no hotter, and the bench started to scorch. If warm-up time is the worry, a Wi-Fi control that starts the sauna before you get home is the better fix.
Frequently Asked Questions
What size heater do I need for a 6 x 8 sauna?
About 336 cubic feet with a 7 ft. ceiling, which calls for an 8 kW heater. With a glass door, it's usually still an 8 kW.
What size heater do I need for a barrel sauna?
Choose Barrel in the calculator and enter the inside diameter and the length of the heated room. The math is 3.14 x radius x radius x length, plus about 3.9 cubic feet per square foot of glass. A 4-person barrel (6 ft. diameter, 6 ft. long) is about 170 cubic feet, a 4.5 or 6 kW heater; a 6-person barrel (7 ft. by 8 ft.) is about 308, an 8 kW, or a 9 kW with a full glass back.
Can I use a wood stove instead?
Yes. Wood stoves are sized the same way, by cubic feet. See our best wood burning sauna stoves guide.
For the full walkthrough, including 6kW vs 8kW, worked examples and replacing an old heater, read What Size Sauna Heater Do I Need? Still unsure? Call or text 1-855-963-5665 with your dimensions.
Electric sauna heaters must be installed by a licensed electrician according to the manufacturer's instructions and local electrical codes.