Sauna Heater Size Calculator (kW by Room Volume)

Why glass counts

Insulated wood walls hold heat, and glass or masonry loses it. Harvia counts every square meter of glass or bare masonry as 1.2 cubic meters of extra room, which is about 3.9 cubic feet per square foot. A full glass door of around 20 square feet adds roughly 80 cubic feet, often enough to move a room up one heater size.

For wood-burning heaters, Harvia also multiplies the volume by 1.5 when the walls are bare logs. If your sauna is solid uninsulated timber, like a barrel, lean toward the bigger heater.

The KIP ratings

The calculator uses Harvia's KIP series because most of the barrel and cabin makers here offer it, including Almost Heaven and Redwood Outdoors. Harvia rates the KIP45 for 106 to 212 cubic feet, the KIP60 for 177 to 283, and the KIP80 for 247 to 424.

The ranges overlap. In the overlap, the smaller heater gets there slowly on a mild day; the bigger one heats faster and handles winter. If the sauna is outside somewhere it snows, I'd take the bigger one.

A bigger heater changes the circuit

Going from 6 to 8 kW costs more than the heater price difference, because it needs a bigger circuit.

More on circuits in the electrical guide, and heater models and prices in the sauna heater guide. To see what a heater costs to run, use the running cost calculator.