Calculator
How big a sauna heater do you need?
Start at about 1 kW for every 45 cubic feet of room, add more for glass or a cold yard, then check the maker's own rating for the heater you like.
Figure about 1 kW of heater for every 45 cubic feet of sauna room, then add a quarter for big windows or uninsulated walls and a bit more for an outdoor sauna in a hard winter. A 6 by 7 by 7 foot room holds 294 cubic feet, so it wants a heater of about 6.5 kW by that rule. Then check the maker's own rating, which is the figure the warranty and the inspector care about. The calculator below runs the arithmetic and suggests a heater from our catalog built in the US.
Try it with your room
What size heater does your sauna need?
Room volume
336 ft³
Recommended heater
7–9 kW
From our listings, that points at Scandia Ultra Medium (6–9 kW).
Rule of thumb: ~1 kW per 45 ft³ of room volume. Always check the heater's own room-size rating and have a licensed electrician confirm the circuit. A 9 kW heater typically needs a 240V/50A non-GFI breaker.
Measure the inside of the room
Measure the room inside, in feet, and multiply the three figures. Measure height from the floor to the ceiling boards, since that's the air the heater has to warm. A 4 by 6 foot room with a 7-foot ceiling holds 168 cubic feet, and a 6 by 8 foot room under the same ceiling holds 336.
Benches and the heater take up some of that space, and we don't subtract them. The makers don't either when they publish a room size.
Our rule runs a little generous, and the maker's rating decides
The makers we list rate their heaters for more room per kW than our rule allows, so the calculator leans toward a heater with headroom. The table lays the numbers side by side. When the calculator lands between two sizes, the maker's rating for the room you have is the one to follow.
| Heater | Output | Maker's largest room | Cubic feet per kW |
|---|---|---|---|
| Scandia Ultra Small | 3 kW | 140 cu ft | 47 |
| Scandia Ultra Small | 4.5 kW | 210 cu ft | 47 |
| Scandia Ultra Medium | 6 kW | 294 cu ft | 49 |
| Scandia Ultra Medium | 7.5 kW | 448 cu ft | 60 |
| Scandia Ultra Medium | 9 kW | 616 cu ft | 68 |
| Finlandia FLB60 | 6 kW | 300 cu ft | 50 |
| Our rule | 1 kW | 45 cu ft | 45 |
Makers' ratings from Scandia's product pages and Finlandia's 2024 brochure, read Oct 10, 2026. Cubic feet per kW is our division of the two.
Glass and a cold yard call for more heat
Glass loses heat faster than an insulated cedar wall, and so does a wall with no insulation behind the boards. Our rule adds 25% for either. An outdoor sauna in a place with hard winters starts each session from a cold room, and the rule adds 15% for that, so a barrel in a Minnesota January gets a bigger heater than the same barrel in Georgia.
The makers' ratings assume an insulated room. If yours has a glass wall, you'll want to size up within the maker's range.
The circuit grows with the heater
A bigger heater draws more current, and the breaker and wire have to match. At 240V, Scandia lists 25 amps for its 6 kW heater, 31.3 for the 7.5 kW and 37.5 for the 9 kW, per its Ultra Medium page. Make sure your panel's got room before you settle on the bigger size, and let the electrician size the breaker to the maker's manual.
For a small room, Scandia's Ultra Small comes in 3 and 4.5 kW and draws less.
Where to buy
Scandia Heaters & Stoves
Scandia Ultra Medium Electric Sauna Heater
Built by a network of US manufacturers, Scandia says
- Electric
- 240V Hardwired
Scandia Heaters & Stoves
Scandia Ultra Small Electric Sauna Heater
Built by a network of US manufacturers, Scandia says
- Electric
- 240V Hardwired
Wood stoves come rated by room size too
A wood stove has no kW rating to divide, so its maker gives a room size instead. Kuuma's Classic Legacy covers 336 to 1,000 cubic feet across three sizes, and Nippa's Legacy runs from a 400-cubic-foot WB-15 to a 1,000-cubic-foot WB-24. Use the calculator's volume, then pick the stove size whose range covers it. Our wood stove guide compares them.
Where to buy
Kuuma Heaters & Stoves
Kuuma Classic Legacy Wood Sauna Stove
Built in Tower, Minnesota
- Wood-Fired
Nippa Heaters & Stoves
Nippa Legacy Series Wood Sauna Stove
Built in Beulah, Michigan
- Wood-Fired
How the calculator works
The calculator multiplies your three measurements, divides by 45 and applies the two multipliers you tick: 1.25 for glass or uninsulated walls and 1.15 for a cold climate. It shows a shopping band from a little under to a little over that figure and suggests a Scandia heater whose range covers it. The makers' ratings in the table come from Scandia's product pages and Finlandia's 2024 brochure, read Oct 10, 2026. Our rule's a starting point, and the maker's manual has the last word.
Common questions
- What size sauna heater do I need for 200 cubic feet?
- About 4.5 kW. America Saunas' rule of about 1 kW per 45 cubic feet gives 4.4 kW for 200 cubic feet, and Scandia rates its 4.5 kW Ultra Small heater for rooms up to 210 cubic feet.
- How many amps does a 6 kW sauna heater draw?
- A 6 kW sauna heater draws 25 amps at 240V, per Scandia's specifications for its Ultra Medium. Electricians commonly put it on a 30-amp breaker, and the heater's manual sets the exact breaker and wire size.
- Is a bigger sauna heater better?
- Up to the maker's rating, a bigger heater warms a room faster and recovers sooner after a ladle of water. Past the rating it cycles off more and needs a heavier circuit, so stay inside the range the maker gives for your room's volume.
We review from makers’ documentation, owner reports and published research. How we choose products and write reviews.
