Pick the right sauna heater size for your sauna room.
Sauna heaters are sized at roughly 1 kW per 50 cubic feet of room, but the volume you use is not the geometric one. Glass and uninsulated stone lose heat far faster than a panelled, insulated wall, so each square foot of glass is counted as about 10 extra cubic feet and each square foot of bare stone or uninsulated wall as 8. A 7 by 5 by 7 ft cabin with a glass door therefore behaves like a 365 cu ft room rather than 245, which pushes it from a 5 kW to a 7.5 kW heater. Keep the ceiling low — 7 ft is the standard — because heat stratifies at the top and every extra foot of height is volume you are paying to heat but not sitting in.
Sauna Heater Size
Effective volume = length x width x height + glass area x 10 + uninsulated area x 8; heater kW = effective volume / 50
Sauna heaters need dedicated wiring, correct clearances to combustibles and code-compliant installation, and sauna use carries health risks for people with cardiovascular conditions or who are pregnant. Use a qualified electrician and seek medical advice if in doubt.
A 4 by 5 by 7 ft cabin is 140 cu ft, so about 3 kW, rising to 4.5 kW with a glass door. Most compact indoor saunas land in the 3-4.5 kW range.
Because heat rises and the useful zone is where your head is when seated on the upper bench. A high ceiling stores hot air above you, lengthening warm-up and raising running cost without improving the sauna.