Size the sauna right, or it never gets hot

Sizing runs in one direction: people → benches → cabin → volume → heater → electrical. Skip a step and the error lands in the last one - usually as a 6 kW heater gasping at a glass-walled 14 m³ room at 7 pm in the rain.

Step 1: people, honestly counted

Count the peak hour, not the brochure: a villa couple is 2; a padel club's post-match wave is 4-6 at once; a hotel spa cycling guided groups wants 8-10. Each seated adult needs ~60 cm of bench; lounging doubles it. Our standard tiers - and their cabins - follow:

Step 2: the 1 kW per m³ rule - and its tropical asterisks

Base rule: ~1 kW of heater per cubic metre of cabin. Then the asterisks that matter here: every square metre of glass behaves like extra volume (add ~1.2 m³ worth per m² of glazing); an uninsulated stone or concrete wall steals heat all evening; and commercial duty wants the next heater up, not the exact match - stone mass is what recovers temperature between guest waves. This is why our cabins pair fixed size-to-heater combinations: the guesswork is pre-made.

Step 3: geometry guests feel

• Ceiling at 2.1-2.2 m: higher wastes heat above heads; lower cramps steam room ergonomics.
• Two bench tiers from 6 people up: heat stratifies, and tiers sell the choice (novices low, veterans high).
• Door swings out, hinge away from the heater - safety code and common sense in one.
• Heater guard rail and lockable wall controller for commercial rooms - staff set 85-95 °C; guests get heat, not switches.
• Ventilation: intake under the heater, exhaust behind the top bench - the tropical anti-mould detail most builds miss.

Electrical, before the electrician asks

6 kW runs on robust single-phase; from 9 kW plan 3-phase. A 15 kW resort heater is a 3×32 A conversation your building engineer wants early - which is why every free layout ships with the electrical reservation sheet. Pair the cabin with cold and the numbers combine: the configurator matches heater and chiller in one pass.