Sauna heater calculator

Find the electric heater size to start with. Enter your room dimensions, account for glass and exposed masonry, then check your electrical supply.

Your sauna room

Measure inside the finished hot room, in metres. For a sloped ceiling, use its average height. Your result updates automatically.

Length m Width m Height m

Glass & construction Total glass area m²

Add the glass door, windows and glass walls together. Measure each width × height. Count each surface once.

Exposed stone, concrete or tile m²

Enter uninsulated wall surfaces, including brick. Exclude the floor, heater stones, glass already entered and log walls selected below.

Wall type

Electrical supply Voltage & phase

Voltage and phase help identify the right heater version. Available circuit capacity must also be confirmed.

How the calculation works

Uses Harvia’s volume-adjustment method and the published ratings of selected Harvia heaters at Saunainter. This calculator covers rooms at least 2 m high; confirm the exact heater version and installation requirements with Saunainter.

Measure the room

Internal length × width × height gives the physical volume. A 2.4 × 2 × 2.25 m room is 10.8 m³.

Account for heat-absorbing surfaces

Each square metre of glass or uninsulated masonry adds 1.2 m³ to the sizing volume. For solid log walls, this calculator multiplies the physical room volume by 1.5 before adding these surface allowances. Do not enter the log walls again as masonry.

Adjusted volume = room volume × wall factor + 1.2 × glass area + 1.2 × masonry area

Match a rated heater range

We compare the adjusted volume with the room ranges published by Saunainter for seven Harvia electric heaters. Among matching models, we suggest the one whose range midpoint is closest to your adjusted volume. This is a starting point from that selection, not a comparison of the entire catalogue.

For example, 10.8 m³ with insulated walls and no glass or masonry falls within the 8–14 m³ range of a 9 kW Cilindro PC90E. Adding glass can change that result.

Check the supply separately

Electrical phase does not reduce the room’s heating requirement. A suitable power rating still needs a compatible regional model, controls and sufficient supply capacity. If the supply cannot support the heater, resolve the supply or room design rather than choosing an undersized heater.

Harvia references at Saunainter

Your result links directly to the matching Harvia model at Saunainter. Product ratings checked 29 September 2026.