Heater power is calculated like this: 1 kW for every cubic metre of interior, plus about 1.2 m³ for every square metre of glass, with headroom for winter added to the result. A sauna with a 2 x 2 x 2.1 m interior, a glass door and a window runs on a 9-10.5 kW heater, and a larger 2.5 x 3 m sauna on a 13.5-15 kW heater. We fit every sauna with a heater matched to its volume, its glazing and your budget, so below we set out the principles we follow rather than recommending a single model.
How do you calculate heater power?
Finnish and Estonian manufacturers use the same formula: power in kW = interior volume in m³ + 1.0-1.2 m³ for every m² of glass. Here is a step-by-step example:
- An interior of 2.0 x 2.0 x 2.1 m is 8.4 m³.
- A glass door and a window together make about 2 m² of glass.
- 8.4 + 2 x 1.2 = 10.8 m³ for the calculation.
- We choose a heater whose range puts this result close to the middle. A 9 kW heater is usually designed for 8-14 m³, so it fits, and a 10.5 kW heater gives headroom for frosty weather.
For a garden sauna in the Polish climate we choose a heater with 15-30% spare power. That way the cabin heats up efficiently in January too.
Which heater for a 2 x 2 m, 2 x 2.5 m or 2.5 x 3 m sauna?
| Interior | Volume | Glass up to 2 m² | Large glazing (approx. 4 m²) |
|---|---|---|---|
| 2.0 x 2.0 x 2.1 m | 8.4 m³ | 9 kW | 10.5-10.8 kW |
| 2.0 x 2.5 x 2.1 m | 10.5 m³ | 10.5-10.8 kW | 10.8-12 kW |
| 2.5 x 3.0 x 2.2 m | 16.5 m³ | 13.5-15 kW | 15 kW |
A glazed front wall gives you a beautiful view from the bench, and we factor it into the heater power so the sauna stays comfortable all year round.
Wall-mounted or tower heater?
| Feature | Wall-mounted heater | Tower heater |
|---|---|---|
| Stones | approx. 20 kg | 55-150 kg |
| Steam after pouring water | short and intense | long, soft and even |
| Heating up | faster | a few to around fifteen minutes longer |
| Space | on the wall, saves floor space | approx. 1 x 1 m of floor |
A tower heater with a large mass of stones gives the most pleasant steam and works superbly in a garden sauna, especially with controls that start heating in advance. A wall-mounted heater is a good choice for compact interiors where every centimetre counts.
Electric or wood-burning heater?
An electric heater gives you convenience: a timer, a thermostat, starting from your phone and an even, consistent temperature. A wood-burning heater gives you ritual, scent and independence from the grid. An electric heater needs a 400 V supply, which we agree in the quote. A wood-burning heater needs a stainless steel chimney and regular flue cleaning, so people choose it above all for its atmosphere and tradition. We help you pick the solution that suits the way you will use your sauna.
What power supply does an electric heater need?
| Heater power | Supply | Circuit protection | Cable |
|---|---|---|---|
| 6-6.8 kW | 400 V, 3-phase | 3×10 A | 5×1.5 mm² |
| 9-10.8 kW | 400 V, 3-phase | 3×16 A | 5×2.5 mm² |
| 12-15 kW | 400 V, 3-phase | 3×20 to 3×25 A | 5×4 to 5×6 mm² |
We agree the power supply in detail in the quote. Connecting the heater requires an electrical qualification, and in tusauna.pl saunas it is carried out by our installation team, together with connecting the controller and lighting.
Which heater brands are available in Poland?
We work with several brands and match the heater to the interior and your budget. Indicative prices for 9 kW heaters in 2026:
| Brand | Character | Indicative price of a 9 kW heater |
|---|---|---|
| Harvia (Finland) | the widest range, from wall-mounted to tower heaters, Wi-Fi controllers, good service availability | approx. PLN 1,300-2,600 (approx. EUR 300-600) |
| HUUM (Estonia) | tower heaters with a large mass of stones, exceptional steam and looks | approx. PLN 7,500-9,000 (approx. EUR 1,700-2,100) including installation |
| Sawo, Narvi (Finland) | solid mid-priced heaters | approx. PLN 2,600-3,000 (approx. EUR 600-700) |
| EOS (Germany) | premium heaters for intensive use | approx. PLN 9,000-10,000 (approx. EUR 2,100-2,300) |
For most garden saunas with moderate glazing, a good 9 kW tower heater from a recognised brand is enough. With large glazing or a bigger volume we choose 10.5-10.8 kW.
How do the controls and remote start work?
For garden saunas we use heaters with electronic controls, which work in frost and let you start heating in advance. A start timer (for example “switch on at 18:00”) works straight away. Starting from an app requires a door sensor under the standard for sauna heaters, so we include it in the design from the outset. We mount the control panel and power module somewhere dry, in the changing room or in the house.
How many stones, and how do you look after them?
- A wall-mounted heater holds about 20 kg of stones, a tower heater 55-150 kg. We use stones made for saunas, 5-10 cm in diameter.
- The stones are stacked loosely, so that they cover the heating elements and air can flow freely.
- With regular use, the stones are rearranged and topped up once a year; crumbled ones are removed from the bottom of the heater.
- We plan ventilation together with the heater: an air inlet by the heater and an exhaust vent on the opposite side.
- Heater power = volume + about 1.2 m³ for every m² of glass, plus headroom for winter.
- A 2 x 2 m sauna: 9-10.5 kW; 2.5 x 3 m: 13.5-15 kW.
- A tower heater gives the most pleasant steam; a wall-mounted one saves space.
- Electronic controls and starting in advance make the sauna convenient all year round.
- We take care of choosing the heater, the power supply and the connection.
Now let’s match a heater to your sauna.