What makes a good sauna
A powerful heater does not make good löyly on its own. In Finland the rules of thumb are about where you sit relative to the stones and the ceiling, how air moves through the room, and how the wood dries. Here they are in one place, with a bench height checker for your own room.
Bench height checker
Enter your ceiling height and the height of the top of the heater stones, both measured from the floor. The heater's installation manual gives the stone height.
1. The law of löyly: sit above the stones
The most quoted Finnish sauna rule is the law of löyly, attributed to the archaeologist and author Sakari Pälsi. The foot bench, where your feet rest, should be clearly above the surface of the heater stones, by about 10 to 20 cm (4 to 8 in). Below that line the air stays cooler and the steam passes over your head before it reaches your feet. A sauna where everyone sits below the stones will never have good löyly, however big the heater.
2. Keep the ceiling close
Heat and steam collect under the ceiling, so the bench has to bring you up to them. A common Finnish guideline puts the ceiling 100 to 120 cm (about 40 to 47 in) above the upper bench. Smaller private saunas sit at the low end; a large public sauna can go higher. Beyond about 130 to 150 cm the steam spreads out above you and the heater spends energy on air nobody sits in.
A quick test: if an adult can stand upright on the foot bench, the benches are too far from the ceiling.
The foot bench sits about 45 cm (18 in) below the upper bench, a comfortable sitting height. Allow about 60 × 60 cm (24 × 24 in) of bench per adult, and make one bench at least 2 m (6.5 ft) long if you want to lie down.
3. A flat ceiling is the safe choice
Steam rises from the stones, spreads along the ceiling to the walls and then sinks and weakens. A ceiling sloping one way creates a steam pocket at its high end, out of reach of the bathers. Beams running across the room deflect löyly; beams running lengthwise guide it. Use ceiling boards of more than 20 mm (¾ in), since the ceiling takes the most heat, and insulate the ceiling first if you are saving energy.
4. Air in near the heater, out down low
Good löyly needs fresh air. In a Finnish field study of public saunas, the best results came from bringing supply air in above or beside the heater and taking it out low: under the benches about 30 cm (12 in) above the floor, or through a gap of about 10 cm (4 in) under the door into the washroom. Mechanical supply and exhaust worked best. Keep the ventilation running after bathing so the room dries. The ventilation guide works out the airflow for your room.
5. Size the heater for the room, not for bragging
The same study used about 1 kW per m³ for saunas under 10 m³ and about 0.7 kW per m³ for larger rooms, with extra for bare stone surfaces and glass. An oversized heater cycles on and off and gives sharp, short steam; an undersized one never gets the stones hot enough. The heater calculator works this out for your room and shows warm-up time.
6. Wood benches, left bare
Use wood with low heat conductivity for benches so they never scorch: aspen, spruce, alder or abachi. In the same field study, wooden benches reached about 70 °C and dried between uses, while tiled benches stayed around 40 °C, collected water and held far more microbes. Tiled or concrete benches should be covered with wood. Leave bench wood unfinished, or use only paraffin oil or a sauna wax; varnish makes it feel like plastic.
Do not seal benches tight against the walls. Air and steam should flow behind them, and the wood should dry after use. Removable or hinged benches make cleaning and changing the heater stones much easier.
New to löyly? See how to use a Finnish sauna for how much water to throw and the etiquette.
7. Clean it and let it dry
Most microbes die within minutes at 50–60 °C, so a sauna that is used hot and dried properly stays clean. Wipe benches after use with an ordinary mild detergent; disinfectant is not needed. Avoid chlorine products in the hot room and never mix them with acids. Wash wood with low pressure, not a pressure washer, and leave the door or vents open until the room is dry.
Checklist
| Principle | Rule of thumb | Why |
|---|---|---|
| Foot bench vs. stones | 10–20 cm above | Feet in the warm zone; even löyly |
| Upper bench to ceiling | 100–120 cm | Head in the steam, not above it |
| Upper vs. foot bench | ≈ 45 cm | Comfortable sitting height |
| Bench space | 60 × 60 cm / person | Room to sit without touching |
| Ceiling | Flat, boards > 20 mm | No steam pockets |
| Fresh air | In above/beside heater, out low | Oxygen and fresh löyly |
| Heater power | ≈ 1 kW / m³ | Hot stones without harsh cycling |
| Bench material | Bare aspen, spruce, alder, abachi | Doesn't burn, dries, stays clean |
Sources
- Lassi A. Liikkanen, "Lauteiden suunnittelu – lyhyt oppimäärä", Sauna magazine, Finnish Sauna Society (Suomen Saunaseura), 2023. sauna.fi
- Lassi A. Liikkanen, "Oikein suunniteltu sisäkatto varmistaa hyvät löylyt", Saunologia, 2016. saunologia.fi
- Saari, M. et al., Terveen saunan tekijät (Elements of a Healthy Sauna), VTT Research Notes 2144, 2002. Field study with the Finnish Sauna Society on its steering group. VTT (PDF)