Sauna Heater Size Calculator: What kW Heater Do You Need?

Enter your sauna's internal size and we'll work out the heater power you need in kilowatts. The rule the trade uses is roughly 1kW of heater for every 1.3 cubic metres of room, then you add load for glass and any cold or uninsulated walls. Undersize the heater and the room never feels like a real sauna; oversize it and you waste money and electricity.

The glass allowance matters because a large glass door behaves like extra room volume to heat. Solid timber barrels and uninsulated cabins lose heat far faster than an insulated cabin, which is why they need a bigger heater for the same internal size. If your figure lands between two common heater sizes, round up, never down.