Sauna Heater Size Calculator

How to use this calculator

1. Enter the sauna room's length, width and height in metres.
2. Add any glass area (doors, windows) and uninsulated stone, concrete or tile area in m².
3. Click Calculate heater size for the recommended power and the closest standard heater.

How sauna heater sizing works

An electric sauna heater is sized from the room's heated volume. The common rule of thumb is about 1 kW per cubic metre for a private home sauna. Cold surfaces that store and lose heat increase the requirement, so this calculator adds 1.2 m³ per m² of glass and applies a ×1.5 factor for stone, concrete or tiled surfaces before sizing.

Sauna volume to heater power

Quick reference for a typical insulated home sauna:

Most home saunas use a 4.5–9 kW heater. Heaters above ~8 kW often need a dedicated higher-amperage circuit.

Frequently asked questions

What size sauna heater do I need?

Allow roughly 1 kW of heater power for every cubic metre of sauna volume. A typical 8–10 m³ home sauna needs about an 8 kW heater.

Why do glass and stone walls need a bigger heater?

Glass, stone, concrete and tile do not insulate like timber panel; they absorb and lose heat, so extra volume is added (1.2 m³ per m² of glass, ×1.5 for stone) to compensate.

Can a heater be too powerful?

Yes. An oversized heater heats the air quickly but may leave the stones too cool for good steam (löyly), and it can cycle on and off. Match the heater to the room volume.