A sauna is a timber room heated by a stove with stones. A steam room is a sealed, tiled room filled by a steam generator. Here's how they differ to build, install and own.
Short answer: a sauna is a timber-lined room heated by a stove full of stones, hot and fairly dry: Harvia’s and Narvi’s manuals recommend about 60 to 80°C. A steam room is a sealed, tiled or acrylic room fed by a steam generator, cooler but very humid: Harvia puts it at 45 to 50°C. They need different rooms, different equipment and different services, and the garden buildings in our data are all saunas.
This page compares them as things to build and own. It doesn’t make health claims for either, and it isn’t medical advice.
Sauna vs steam room at a glance
| Sauna | Steam room | |
|---|---|---|
| What makes the heat | An electric heater or wood stove heating a bed of stones | A steam generator, installed outside the room, piping steam in |
| Air temperature | About 60–80°C recommended in Harvia’s and Narvi’s manuals; controls go to 110°C or more | 45–50°C (Harvia) |
| Humidity | Dry air, raised by throwing water on the stones | Very humid: an encyclopedia source says it approaches 100% |
| What the room is made of | Timber panelling over insulation and a foil vapour barrier | A water-resistant surface such as tile, marble or moulded acrylic, fully enclosed (Mr.Steam). Harvia says no wood inside |
| Ceiling | Timber-panelled, like the walls | Sloped or curved so condensation runs off (Harvia: at least 15°) |
| Water and drainage | No water connection to the heater: water is ladled on by hand. Harvia’s manual says water dripping onto the floor should run to a floor drain | A water supply to the generator and a drain; a floor drain in the room |
| Electrics | Connected by a qualified electrician, the heater makers say; almost every heater needs its own circuit | Supply for the generator; Vidalux’s steam shower cabin needs one 13 A connection |
| Where it goes | Indoors, or in the garden as a barrel, cabin or pod | Indoors. One maker says not to install its generator outdoors or where water could freeze |
Sources: Harvia: Cilindro Pro electric sauna heater, instructions for installation and use (PDF hosted by zoechling-holz.at); Narvi: Velvet electric sauna heater with Flow controller, installation and instruction manual (EN section); HUUM: UKU 4.1 (Wi-Fi/Local) sauna control system user manual, US edition (PDF); Harvia: How to build a steam room; Wikipedia: Sauna (encyclopedia, not a manufacturer source); Mr.Steam (US maker): Plan your project; Mr.Steam (US maker): MS residential steam generator installation and operation manual (PDF pur100597a); Vidalux (UK steam shower seller): Essence / Clearwater installation manual (PDF); HUUM: DROP electric sauna heater user manual (EU, 2025). Checked 30 September 2026.
How each one makes heat
A sauna has a heater in the room: an electric heater or a wood-burning stove, with stones on top or around it. The heater warms the air and the stones, and you throw a little water on the stones to make a burst of steam. Harvia says the air in a sauna becomes dry as it warms, which is why the water is thrown. Compare what’s on sale on sauna heaters and wood-burning sauna stoves.
A steam room has no heater in the room at all. A steam generator boils water somewhere nearby and sends the steam in through a pipe to a steam head, which Mr.Steam puts 6 to 12 inches above the floor. Harvia says the generator goes in a dry place with a floor drain and ventilation, at the same level as the steam room, preferably less than 6 metres away and no more than 10. Mr.Steam, a US maker, says its generator must never be installed inside the steam room itself.
Sources: Harvia: Cilindro Pro electric sauna heater, instructions for installation and use (PDF hosted by zoechling-holz.at); Harvia: How to build a steam room; Mr.Steam (US maker): MS residential steam generator installation and operation manual (PDF pur100597a); Mr.Steam (US maker): Quick installation guide (PDF). Checked 30 September 2026.
Temperature and humidity
The two rooms sit at opposite ends. A traditional sauna is hot: Harvia’s heater manual says about 65 to 75°C is suitable and Narvi’s recommends 60 to 80°C, with Harvia describing 80 to 100°C as a high temperature at which the air can feel dry even with water on the stones. A steam room is much cooler on the thermometer, at 45 to 50°C according to Harvia, but the air is full of steam.
There’s more on what the makers recommend, and the same temperatures in Fahrenheit, in sauna temperature.
Sources: Harvia: Cilindro Pro electric sauna heater, instructions for installation and use (PDF hosted by zoechling-holz.at); Narvi: Velvet electric sauna heater with Flow controller, installation and instruction manual (EN section); Harvia Support: What is the correct sauna temperature?; Harvia: How to build a steam room. Checked 30 September 2026.
How the rooms are built
The materials are close to opposites, which is why you can’t simply turn one into the other.
A sauna room is insulated, lined with a foil vapour barrier and panelled in timber, with ventilation and timber benches. Our guide to how to build a sauna goes through each layer from the heater makers’ manuals.
A steam room has to hold water vapour in:
- Harvia says no organic building materials, such as wood, may be used inside a steam room.
- Mr.Steam says the room must be completely enclosed, with full walls, door, floor and ceiling, and that the walls and ceiling need a water-resistant, non-corrosive surface such as tile, marble or moulded acrylic.
- The ceiling slopes. Harvia says it must be curved or mono-pitch at an angle of at least 15 degrees; Mr.Steam says it should be sloped so condensate doesn’t drip.
- There’s a drain. Harvia says a steam room must have a floor drain, or a floor that slopes to the doorway of a room that has one.
- The door is glass or plastic. Harvia specifies 8 mm tempered glass, 8 mm laminated and tempered glass, or polycarbonate.
- Ventilation is simpler at home: Harvia says a steam room in a private home doesn’t need separate ventilation if the adjoining wet room has mechanical supply and exhaust ventilation.
Sources: Harvia: How to build a steam room; Mr.Steam (US maker): MS residential steam generator installation and operation manual (PDF pur100597a). Checked 30 September 2026.
Plumbing, electrics and sizing
A sauna heater needs power but no water connection. Harvia, HUUM and Narvi all say an electric heater must be connected by a qualified electrician. A 13 A socket supplies about 3 kW and most sauna heaters are 4.5 kW or more, so almost every one needs its own circuit: our electrical supply calculator shows what each size draws. The cheapest electric sauna heater in our data is £355.
A steam room needs plumbing as well as power. Mr.Steam says a steam shower needs a water line to the generator, a steam line from the generator to the shower and a drain line. At the small end, Vidalux says its self-contained steam shower cabin needs one 13 A mains connection and hot and cold water supplies at 1 to 3 bar, and lists a 2.8 kW steam generator on one model.
Sizing works differently too. A sauna heater is sized to the room’s volume, with extra for glass and uninsulated walls: use the heater size calculator. A steam generator is also sized from the room’s volume, but adjusted for what the walls are made of: Mr.Steam says each material holds heat differently, and adds 50% for natural stone, glass block or concrete.
Mr.Steam’s figures come from a US maker’s manual, so treat them as a guide to what’s involved, not as UK installation requirements. Whoever supplies your generator will have their own.
Sources: Harvia: Cilindro Pro HPCE2642 EN - Instructions for installation and use of electric sauna heater (PDF hosted by Zöchling Holz); HUUM: DROP electric sauna heater user manual (EU, 2025); Narvi: Installation and instruction manual, Narvi Velvet Electric 9.0 kW / 10.5 kW; Mr.Steam (US maker): Plan your project; Vidalux (UK steam shower seller): Essence / Clearwater installation manual (PDF); Vidalux (UK steam shower seller): Essence 900 product page; Mr.Steam (US maker): MS residential steam generator installation and operation manual (PDF pur100597a); Harvia Support: How do I select the correct heater power?. Checked 30 September 2026.
Can you have a steam room in the garden?
Garden saunas are an established product: we list 489 of them from 23 UK retailers. We haven’t found an outdoor steam room among those retailers’ sauna ranges, and the makers’ guidance we read points indoors. Harvia’s steam room guide requires a floor drain and refers to an adjoining wet room with mechanical ventilation. Mr.Steam says its generator must not be installed outdoors, or anywhere water could freeze and burst the pipes.
If it’s steam you want in the garden, there are two closer matches:
- A traditional sauna with water on the stones. You control the humidity yourself with the ladle. Every barrel, cabin and pod with a stove and stones works this way.
- A combi heater. Harvia describes its Combi heaters as an electric sauna heater combined with a built-in steam generator, so one room can run hot and dry or milder and more humid. The controller caps the two together: temperature in °C plus humidity percentage can’t exceed 140. Tylö’s US manual for its Sense Combi describes a water reservoir you fill by hand before starting the heater. We don’t have UK prices for combi heaters in our data yet.
Portable fabric “steam sauna” pods are a different product again: see the section on them in sauna pods.
Sources: Mr.Steam (US maker): MS residential steam generator installation and operation manual (PDF pur100597a); Harvia: How to build a steam room; Harvia: Combi heaters; Harvia Support: Air humidity and temperature settings in Combi heaters; Tylö (US site): Sense Combi sauna heater installation manual (PDF). Checked 30 September 2026.
Heat-up time and running
Harvia and HUUM both say a properly insulated sauna with the right size of heater takes about an hour to reach bathing temperature, though retailers quote less for some models. For a steam generator, Mr.Steam says steam begins to appear in about five minutes, which isn’t the same thing as the room being up to temperature.
We publish running costs for saunas, worked out from each heater’s output and the Ofgem price cap: see the running cost calculator. We don’t have the equivalent data for steam generators, so we don’t quote a figure. A generator also needs looking after: Mr.Steam offers an automatic flush that drains the generator after each use.
Sources: Harvia: Cilindro Pro electric sauna heater, instructions for installation and use (PDF hosted by zoechling-holz.at); HUUM: DROP electric sauna heater user manual, EU edition (PDF); Mr.Steam (US maker): MS residential steam generator installation and operation manual (PDF pur100597a). Checked 30 September 2026.
Which should you choose?
- Choose a sauna if you want it in the garden, you like hot, dry heat that you can soften with water on the stones, or you don’t want to add plumbing and a drain.
- Choose a steam room if you’re fitting out a bathroom or wet room indoors, you want a lower temperature with heavy steam, and you’re already tiling and plumbing the space.
- Want both? A combi heater in a sauna room is the nearest thing to one room that does both. Otherwise they’re two separate rooms.
If you’re leaning towards a sauna, start with how to choose a garden sauna or home sauna: indoor or garden?.