Sauna heater size calculator
Room dimensions + insulation → recommended heater kW, BTU/hr, and breaker size. Runs 100% in your browser — nothing is sent anywhere.
How the math works
Industry rule of thumb: 1 kW per 40–60 cubic feet of sauna volume, depending on insulation (poor ÷40, average ÷50, excellent ÷60). Outdoor/unheated spaces get a 25% bump; significant glass adds ~1.5 kW. The result rounds up to the nearest standard heater size (3, 4.5, 6, 8, 9, 10.5, 12, 15 kW) — slightly oversized beats underpowered, since an undersized heater runs flat-out and still leaves you lukewarm. BTU/hr = kW × 3,412.
Ready to look at actual saunas? Browse the sauna lineup or run the 5-year cost calculator next.
This guide is for general information only and isn’t medical advice. Talk to your doctor before starting heat or cold therapy.