1. Power decides

Electric heaters of 6 to 9 kW connect to a three-phase 400 V supply with a dedicated breaker, typically 3 × 16 A. The supply must be installed by a qualified electrician who issues an inspection certificate. Without it we will not connect the heater – and your insurer would ask for it after any incident.

If the flat has no three-phase supply, ask the building manager and your distribution operator whether the capacity can be increased. If not, an infrared cabin on 230 V remains. Small 230 V heaters for cabins up to roughly 4 m³ exist but are a compromise – we handle those case by case on request.

2. Ventilation

A sauna needs fresh air, otherwise it feels stuffy and the wood dries slowly. Air comes in low near the heater and leaves on the opposite side – either higher on the wall or under the bench. In a flat the outlet is usually connected to the bathroom extract. Leave the door open after a session so the cabin dries.

3. Moisture and protecting the structure

Behind the cladding there is always an aluminium vapour barrier. It keeps moisture out of the wall and reflects radiant heat back inside. The cladding sits on battens with a ventilated gap. The floor under the sauna should be washable – tiles are ideal, carpet and laminate are not. A floor drain is not needed unless you shower inside the sauna.

4. Location and dimensions

• Bathroom: the most common solution, with the shower right there. Allow space for the door, which opens outwards.
• Cellar or utility room: check moisture levels and whether you can vent to the outside.
• Loft: mind the head height and whether the structure carries the load.

A height of 190 to 210 cm is ideal. A taller cabin only adds volume: heat stays at the top and your feet stay cold. A corner layout with an angled entrance makes use of awkward floor plans.

5. Permissions and neighbours

Inside a flat this is usually not structural work, so a building permit is rarely needed. But if you touch shared services, risers or ventilation, you need the consent of the owners’ association or building manager – and of the landlord if you rent. Increasing the connected load goes through the distribution operator.

What it costs

A custom indoor sauna starts at 5 766 €, an infrared cabin at 4 382 €. Below are the sizes that typically fit a flat.

Step by step

1. Measure the space including height and room for the door to swing out.
2. Check whether you have 400 V and which breaker is free; if not, consider an infrared cabin.
3. Plan ventilation: where air comes in and where it leaves.
4. Check the floor and how moisture will dry out.
5. Obtain consents if shared parts of the building are affected.
6. Send your configuration with photos of the site – the quote arrives within 48 hours.

Frequently asked questions

What is the smallest sensible size?

About 120 × 120 cm for one or two people, comfortably two from 150 × 150 cm. A bench shorter than 180 cm is not usable for lying down.

How long does installation take in a flat?

The sauna itself is usually a one-day job. The electrical installation has to be ready beforehand.

How much does a sauna in a flat consume?

An 8 kW heater about 9 kWh per session, roughly €2.25 at €0.25/kWh. An infrared cabin about a fifth of that.

Will it be noisy or smell through the flat?

An electric heater is silent. The scent of wood is noticeable mainly in the first weeks and after a session with the door open – which is why ventilation matters.