A sauna heater is sized at roughly 1 kW per cubic metre of room, then corrected upward by about 30 % for every large glass wall and 10 % for uninsulated stone or tile. A 2.4 × 2.0 m sauna with a 2.2 m ceiling is 10.6 m³ and takes a 9 kW heater; the same room with a full glass wall takes 10.5 or 12 kW. Above about 4.5 kW the heater needs three-phase power, which decides what an apartment can have. This guide gives the rule, the corrections, the warm-up times and the heaters we fit in Dubai.
The rule and the corrections
| Room | Volume | Timber walls | With glass door | With glass wall |
|---|---|---|---|---|
| 1.8 × 1.6 × 2.1 m, 2–3 seats | 6.0 m³ | 6 kW | 6 kW | 8 kW |
| 2.4 × 2.0 × 2.2 m, 4–5 seats | 10.6 m³ | 9 kW | 9 kW | 10.5–12 kW |
| 3.0 × 2.4 × 2.3 m, 6–8 seats | 16.6 m³ | 12 kW | 12–15 kW | 15 kW or 2 × 9 kW |
| 3.6 × 2.6 × 2.3 m, 8–10 seats | 21.5 m³ | 15 kW | 2 × 9 kW | 2 × 10.5 kW |
Glass loses heat by radiation the way timber does not; a 10 mm tempered wall is roughly the thermal equivalent of adding 30 % to the room. Stone, tile or concrete surfaces inside the room absorb heat and give it back slowly, so a sauna with a tiled floor and a stone feature wall gets another 10 %. Ceiling height matters more than floor area: every 10 cm above 2.2 m is heat you pay for and do not sit in. The custom sauna page lists the room sizes we build most.
Why 9 kW means three-phase
A 9 kW heater at 230 V single-phase draws about 39 A continuously, more than a domestic single-phase circuit is designed to carry for an hour. Split across three phases at 400 V it draws about 13 A per phase, which is a routine dedicated circuit. That is why heaters from 6 kW upward are wired three-phase, why villas take them easily, and why standard apartments with 60 to 100 A single-phase supplies are limited to a 4.5 kW compact heater or an infrared cabin. The apartment sauna guide covers the tower case, and the DEWA approval page the submission for the new circuit.
Warm-up time
A correctly sized heater brings a timber sauna from 22 °C to 80 °C in 35 to 50 minutes, a glass-walled room in 45 to 60. Undersizing does not save electricity; the heater runs continuously and the room settles at 65 °C. Oversizing by one step is harmless: the heater reaches temperature sooner and cycles more. Where a client wants a sauna ready in twenty minutes, two heaters or a heater with a large stone mass and a pre-heat schedule on the app control do it.
Stones, mass and löyly
The stones are the sauna. A heater with 20 kg of stones gives a short, sharp burst of steam when water is ladled; a tower heater with 60 to 100 kg gives a long, soft löyly and stays hot between sessions. Tower heaters cost more, take a little more power to heat their mass, and are what we fit in most family saunas in Emirates Hills and Dubai Hills. Olivine diabase or peridotite stones, 5 to 10 cm, replaced or re-stacked at the annual service.
Heaters we fit in Dubai
Harvia, EOS, Tylö, Helo and Sentiotec: European manufacturers with certification, controls that integrate with the room, and parts we hold in Dubai. Wall-mounted heaters for compact rooms, tower heaters for family saunas, and combi heaters with a water tank for a humid Finnish-style room. Controls range from a wall panel with a timer to app-connected units with schedules and a pre-heat. We do not fit unbranded heaters, because a heater is the one thing in a sauna that can start a fire, and its certification, its high-limit cut-out and its guard rail are not places to save AED 2,000.
Installation rules that go with the sizing
A dedicated circuit with a breaker matched to the heater, heat-resistant SiHF cable in the hot zone, an isolator outside the room, a 30 mA RCD, the contactor and control unit outside the hot zone, a guard rail, and clearances to timber as the manufacturer specifies. All of it is on the drawing before the DEWA submission and checked at commissioning.
Running cost by heater size
At the upper DEWA residential slab, a 9 kW heater used ninety minutes three times a week costs AED 50 to 55 a month; a 12 kW heater in a glass room, AED 65 to 75; two 10.5 kW heaters in a large family room, AED 110 to 130. The sauna cost guide puts these against the build cost.
Send the room dimensions and a photo of the DB board and we will reply with the heater size, the phase and the warm-up time for your room.
