The sauna itself
Sauna. A hot room heated to a high air temperature with low humidity, traditionally with a stove or electric heater holding a mass of stones. Sauna culture in Finland was inscribed on UNESCO’s list of intangible cultural heritage in 2020.
Traditional sauna (Finnish sauna). A sauna heated by a stone heater, electric or wood-burning, where water is thrown on the stones for löyly. Heater manufacturers commonly recommend a setting of around 65 to 80 °C; the exact range varies by maker.
Löyly. The Finnish word for the steam that rises when water is thrown onto hot sauna stones, and for the feeling of heat it brings. It briefly raises the humidity much more than the temperature. See how a sauna heats.
Kiuas. Finnish for the sauna heater or stove, the “heart” of the sauna.
Lauteet. Finnish for the sauna benches. The upper bench is where the heat is; a lower bench or step often serves as the foot rest.
Stratification. The layering of hot air under the ceiling and cooler air near the floor. It is why sauna benches sit high and ceilings stay modest.
Feet above the stones. A Finnish rule of thumb, restated in the Finnish Sauna Society’s magazine, that the bather’s feet should rest above the level of the heater stones so the heat feels more even from head to toe. It comes from naturally ventilated saunas, and heater design and ventilation can change the result.
Vihta or vasta. A whisk of leafy birch twigs used to gently beat the skin in a traditional Finnish sauna.
Smoke sauna (savusauna). The oldest Finnish sauna type, heated by a large stove with no chimney; the smoke is let out before bathing. Rare outside Finland.
Heaters and stones
Electric sauna heater. A heater with resistance elements that warm the air and the stones, run from a thermostat and timer. See choosing and sizing a sauna heater.
Wood-burning heater (wood stove). A heater fired with wood, with a firebox, a stone compartment and a flue. Its clearances and flue are set by its manufacturer, and approval and installation requirements are confirmed for each site.
Wall-mounted, floor-standing and tower heaters. Compact heaters hung on the wall; free-standing heaters on legs; and tall cylindrical heaters holding a large stone mass, often chosen as a feature of the room.
Heat-storage heater. A heater with an insulated, closed stone chamber that keeps its stones hot on standby so the room is ready quickly, at the cost of continuous standby energy use.
Combi heater. A heater with a built-in water reservoir that adds humidity for a lower-temperature, more humid session. Not the same as a hybrid sauna.
Stone load. The quantity of stones a heater holds, from about 20 kg in small wall heaters to more than 200 kg in the largest models.
Olivine diabase. A dense, dark igneous rock and the classic Finnish sauna stone, sold split-face (angular) or rounded. See sauna stones.
Split-face stones. Angular stones with rough fracture faces, the standard stone for most heaters.
Rounded stones. Stones tumbled smooth, used as the top layer or, in some heaters, as the specified stone (Harvia specifies rounded 5–10 cm stones for its Spirit heaters).
Element. The electric heating element inside the heater. Elements sit among the stones in many heaters and are separated from them in others.
Heater guard. A timber rail or barrier around the heater to stop people touching it.
Clearances (safety distances). The minimum distances the heater manufacturer specifies between the heater and walls, ceilings, benches and floors. They are model-specific.
Overheat protector (high-limit cut-out). A safety device that switches the heater off if the temperature gets too high. Manufacturers say the cause must be found before it is reset, and some reserve resetting for a person qualified for electrical work.
Control unit and sensor. The panel that sets temperature and time, and the temperature sensor it reads, usually mounted high near the heater. Some heaters have built-in controls; others need a separate control unit.
Sizing and planning
Room volume. Length × width × height of the hot room, in cubic metres. Heaters and steam generators are rated for a range of room volumes.
Correction factor (volume allowance). An amount added to the room volume for glass, tile, brick, concrete or stone surfaces, which absorb or lose more heat than insulated timber. Many sauna heater manufacturers add about 1 to 1.5 m³ for each square metre of such surface, and some add more for solid masonry. Methods vary by brand, so the chosen heater’s manual sets the figure.
Heat-up time. The time a heater takes to bring the room and its stones to temperature, typically about an hour for a correctly sized heater in an insulated room.
Prefab sauna (prefabricated sauna, sauna kit). A sauna made in a factory as a complete design and assembled on site, such as the LeisureCraft barrel, cabin and modern models. See prefab saunas.
Custom sauna. A sauna designed and built for a particular space, from the room’s proportions to the benches, timber and glazing.
Barrel sauna. A round sauna built from timber staves held by bands, designed to stand outdoors.
Thermally modified timber (thermo timber). Timber heated in a controlled, low-oxygen process, at about 180 to 220 °C depending on the process and class, to make it more stable and resistant to rot. It is darker, and it is not termite-resistant.
Infrared and hybrid
Infrared sauna. A room warmed by infrared emitters that heat the people in it directly, so the air stays cooler, typically around 40 to 65 °C. There are no stones and no löyly.
Emitter (infrared panel). The panel that radiates infrared heat. Emitters are rated for particular conditions; those made for a hot sauna differ from those for a low-temperature infrared cabin.
Near, mid and far infrared. Bands of infrared wavelength. The industry uses the names inconsistently, and “full spectrum” emitters combine bands in varying proportions.
Hybrid sauna. In our work, one room with a traditional stone heater and infrared emitters, so it can be used either way. See hybrid saunas.
Steam rooms
Steam room. A sealed, fully waterproofed room filled with steam at close to 100 per cent humidity and a much lower air temperature than a sauna.
Steam generator. The small electric boiler, outside the room, that makes the steam and pipes it in.
Steam outlet (steam head or nozzle). Where the steam enters the room, usually low on a wall and placed so the steam does not blow onto people. Its height is set by the generator manufacturer.
Blowdown, drain and flush. The cycle in which a steam generator empties and rinses its tank to remove mineral residue. Many generators do this automatically after use, and they need the power left on to do it.
Scale. Mineral deposits left behind as water boils, mainly calcium and magnesium. A common cause of steam generator faults, which is why manufacturers set descaling and flushing routines. See steam generators and water quality.
Descaling. Removing scale from a generator, by the method its manufacturer specifies.
Water softener. Equipment that removes the minerals that form scale. Required by several steam generator manufacturers for commercial or public steam rooms, and recommended where water is hard. It does not replace descaling.
Water hardness. The amount of dissolved calcium and magnesium in water, usually reported in milligrams per litre as calcium carbonate, or in German degrees (°dH).
Ceiling slope. The fall built into a steam room ceiling so condensation runs down the walls instead of dripping on bathers. Harvia, for example, specifies at least 15°.
Vapour barrier and waterproofing membrane. The layers that keep moisture from passing through the walls and ceiling into the building. Steam rooms need far more than shower-grade waterproofing.
Commercial terms
Commercial-rated (commercial duty) equipment. Heaters and generators designed, tested and warranted for many hours of daily use in public facilities.
Duty cycle and maximum on-time. How long equipment runs, and the limits on continuous operation built into its controls. For example, Harvia’s Xenio control allows 1–6 hours for family saunas and 1–12 hours for public saunas in apartment buildings, while its Fenix control offers 12, 18 or 24 hours for commercial use.
Operator checklist. The daily, weekly and periodic checks a facility runs to keep rooms clean, safe and working. Ours is in the commercial guide.