The basic rule for choosing an electric sauna heater is simple: a well-insulated hot room needs about 1 kW per 1 m³ of volume, and glass or stone walls push that number up. Then you decide on the power supply (230V single-phase or 400V three-phase) and the controls — built into the heater or a separate panel, possibly with Wi-Fi. Here’s how to work through it step by step.
Why go electric
- No chimney. For saunas inside a house, apartment, villa or hotel it is practically the only realistic option.
- Precise temperature. A thermostat holds the setting; no logs to add.
- Timers and remote control. Pre-heat on a schedule or start the sauna from your phone.
- Clean. No ash, no soot, no woodpile.
That’s why electric heaters are the standard in indoor saunas, and a popular choice for outdoor saunas wherever the electrical supply allows.
Sizing: kW and m³
The general rule
- Calculate the hot room volume: width × length × height. For example, 2 × 1.8 × 2.1 m ≈ 7.6 m³.
- For a well-insulated timber room: roughly 1 kW per 1 m³.
- Check the manufacturer’s table. Every heater lists a minimum–maximum room volume; yours should fall inside it, ideally near the middle.
Corrections for glass and stone
Uninsulated surfaces soak up heat, so they’re added to the calculation:
- Each 1 m² of glass, stone, tile or concrete adds about 1.2 m³ to the volume.
- A glass door counts too — a typical one is around 1.3–1.6 m².
- Solid log walls without insulation: multiply the volume by about 1.5.
Example: a 7.6 m³ room with a 1.5 m² glass door and a 2 m² stone feature wall. Correction: (1.5 + 2) × 1.2 = 4.2 m³. Effective volume ≈ 11.8 m³ — so you need a heater in the 9–10.5 kW class, not 6 kW.
| Effective volume | Approximate heater output |
|---|---|
| 2–4.5 m³ | 2.3–3.6 kW |
| 4–7 m³ | 4.5–6 kW |
| 7–12 m³ | 8–9 kW |
| 11–18 m³ | 10.5–15 kW |
| 18 m³ and up | 18 kW and up |
In a cabin sauna with a panoramic glass facade, this correction matters a lot — the glass changes the numbers noticeably.
Power supply: 230V or 400V
- 230V (single-phase). For smaller heaters: many models from about 2.3 to 9 kW can be wired either single-phase or three-phase. But 6–9 kW on one phase means a high current, so the cable size and breaker must be rated for it.
- 400V (three-phase). The load is split across three phases, so the cable can be thinner. Heaters from about 10.5 kW upwards are usually three-phase only.
The wiring diagram, cable size and breaker should be chosen by a qualified electrician according to the heater’s manual. Before you buy, check what supply your house has and how much capacity is available.
Controls: built-in or separate panel
Built-in controls
Thermostat and timer knobs sit on the heater itself. Simple and affordable, fine for small saunas. Examples include Harvia’s Vega and KIP series and SAWO’s “NB” versions (Nordex, Scandia, Cumulus).
Separate control panel
The panel is mounted outside the hot room — in the changing area or on a wall. Benefits:
- set the exact temperature without stepping into the heat;
- delayed-start timer, plus lighting and ventilation control;
- a display or touchscreen;
- on some panels, Wi-Fi and app control.
Examples: Harvia Xenio and Xenio WiFi, SAWO Saunova and Innova. Always check that the panel is compatible with your heater model — some heaters only work with a separate control unit.
Brands and example ranges
| Brand | Example series | What stands out |
|---|---|---|
| Harvia (Finland) | Vega, KIP, Cilindro, Legend, Virta, Spirit | The widest range, from compact wall units to large stone towers |
| SAWO (Finland) | Tower, Nordex, Scandia, Krios, Cumulus | Tower heaters, bench-integrated models, big stone capacity |
| Fanlan | SA, SAV, SCA, DM, FT | Wide choice of electric heaters for home and commercial saunas, up to 30 kW |
All of these brands are in our sauna heaters catalogue, with output, suitable room volume and stone capacity listed for each model. Barrel Sauna sells and installs Harvia and SAWO heaters, and we’re happy to advise on the others too.
Stones and steam
Stone capacity shapes the steam. Compact wall-mounted heaters hold around 20 kg of stones — they heat up fast but the steam is sharper. Models with a large stone load (such as SAWO Krios or Harvia Legend) hold heat longer and give softer steam. Check the stones once a year and replace any that crumble.
Installation checklist
- Respect the minimum clearances to walls, ceiling and benches given in the manual.
- Fit a wooden guard rail around the heater to prevent accidental contact.
- Ventilation: the fresh-air inlet is usually low down, near the heater.
- Mount the thermostat sensor exactly where the manual says, or the temperature reading will be off.
FAQ
What size heater do I need for an 8 m³ sauna?
With good insulation and no glass, typically 8 kW. If there’s a glass door or stone cladding, apply the correction and look at 9 kW models.
What if my house has no three-phase supply?
Many small and mid-size heaters (up to around 9 kW) also support single-phase connection. Have an electrician confirm the cable and breaker.
Why would I want a Wi-Fi control panel?
You can switch the sauna on from your phone on the way home so it’s ready when you arrive, and monitor the temperature and timer remotely.
Does an electric heater work in an outdoor sauna?
Yes. Barrel, cube and cabin saunas run very well on electric heaters; the main requirement is a sufficient electrical supply.
Are electric sauna heaters safe?
With the correct output, proper installation and professional wiring — yes. Most control units also include an automatic shut-off timer.
Let’s size the heater for your sauna
Send us the room dimensions, the area of glass and stone, and the type of electrical supply you have. We’ll calculate the output and pick a matching Harvia or SAWO heater and control panel. Message us on WhatsApp for a free consultation and calculation.
