Tool

Sauna heater size calculator

Enter your room size to see two published rules of thumb for heater power, and which heaters in my sizing table list a window that contains your room.

Room widthftRoom depthftCeiling heightftGlass or stone surfacesq ftUninsulated glass, tile or stone adds to the load in both methods.

Room volume210 cu ft

With glass allowance (retailer method)210 cu ft → about 4.2 kW

HUUM method210 cu ft → about 5.9 kW

Heaters whose listed volume window contains the retailer-method volume

Harvia KIP, 4.5 kW listed for 100–210 cu ft
HUUM Drop, 4.5 kW listed for 110–240 cu ft
Amerec Designer SL2, 4.5 kW listed for up to 210 cu ft
Saunum Air 5, 4.8 kW listed for up to 212 cu ft
Harvia KIP, 6 kW listed for 170–300 cu ft
Finlandia FIN-60, 6 kW listed for up to 300 cu ft
HUUM Drop, 6 kW listed for 180–350 cu ft

Where the numbers come from

The retailer method is the Topture guide's: width times depth times height in feet, plus about 50 cu ft for every 10 sq ft of glass or stone, then about 50 cu ft per kW. The HUUM method adds the uninsulated surface area (glass, tile, log walls) to the room volume with a factor of 1 in metric, which I converted at 3.28 cu ft per sq ft, then matches 1 kW to each cubic meter, or about 35.3 cu ft. The two methods give different answers, and I explain why in best electric sauna heater.

What the heater list is

It is the sizing table from that page: the volume window each maker or retailer lists for a heater. It is not a recommendation, and a room near the top of a window makes the heater work harder. Supply voltage can change the window (the HUUM Steel is listed at different volumes on 208V and 240V), and none of this replaces the heater's own manual or an electrician. Where a heater lists only "up to" a volume, the table shows it that way.