Sauna Blueprint

Planning tool

Sauna heater sizing calculator

Most sizing calculators apply one coefficient and hand you a single number. That number cannot be right for every brand, because the manufacturers do not publish the same rule. This one applies each method separately, shows you the arithmetic, and quotes the source it came from.

Units
Your sauna room, measured inside

Measure the finished interior — not the exterior of a kit, and not a manufacturer’s published volume.

Uninsulated surfaces

Total area of glass, brick, tile, stone, or concrete inside the room. These absorb heat, and every manufacturer treats them as extra volume. A typical full-glass sauna door is roughly 15 ft².

What each manufacturer’s own method gives

Harvia’s published method

Published for Harvia, Tylö, Finnleo

Calculated volume6.9 m³245 ft³
Implied output6.9 kW
Show the arithmetic
  1. Room volume: 7 × 5 × 7 = 245.0 ft³
  2. Calculated volume: 6.94 m³ → 6.9 kW at 1 kW per m³
  • “An average of 1 kW of heater power is required for each cubic metre of sauna volume.”
    Source
  • “One square metre of stone, glass or similar non-insulated surface increases the heater power requirement as much as if the sauna room volume were increased by 1.2 cubic metres.”
    Source
  • “If the interior walls of the sauna room are made of non-insulated logs, the corresponding factor is 1.5.”
    Source

HUUM’s published method

Published for HUUM

Calculated volume6.9 m³245 ft³
Implied output6.9 kW
Show the arithmetic
  1. Room volume: 7 × 5 × 7 = 245.0 ft³
  2. Calculated volume: 6.94 m³ → 6.9 kW at 1 kW per m³
  • “As a rule of thumb, heating 35.3 ft³ / 1 m³ of the steam room requires 1 kW of power.”
    Source
  • “In the case that there are uninsulated walls made of bricks, tiles, glass or logs in the steam room, an additional volume of 3.3 ft³ per each such square feet of the wall should be added to the cubic size of the steam room.”
    Source

Heaters in the directory that cover 6.9 kW

Matched on published output against the higher of the two calculated requirements, smallest sufficient model first. This is not a ranking and no commission is involved in the order. Always confirm the model’s own room-volume range in its manual — several manufacturers publish a minimum room size as well as a maximum, and an oversized heater in a small room is its own problem.

This is a planning estimate produced by applying each manufacturer’s own published sizing method to the dimensions you entered. It is not a specification and not an electrical instruction. Confirm the final heater choice against that model’s manual and have the circuit specified by a licensed electrician against your local code.