Guide · Traditional saunas

Smoke saunas and heat-storing stoves

Ask Finns which sauna gives the best löyly and many will name one of two: the smoke sauna, or a sauna with a heat-storing stove that is fired once and then left to give steam for hours. Both are almost unknown outside the Nordic countries. Here is how they work and what it takes to have one.

Three ways to heat a sauna

Every sauna stove heats stones, but they differ in when the heating happens.

Continuous stoveHeat-storing stoveSmoke sauna
Finnish namejatkuvalämmitteinenkertalämmitteinensavusauna
Fire while you batheYes, or the electric heater runsNo, fired beforehandNo, fired beforehand
ChimneyYesYesNone; smoke fills the room
Stone massUsually 20–130 kgAbout 60–380 kgA large pile of stones
Heating timeUnder an hourLonger; the heavy stone mass must heat throughTypically 4–6 hours, plus at least an hour to settle
Heat lastsWhile the heater runsSeveral hours, even until the next morningThe whole bathing session
EffortLowMediumHigh; a day's ritual

Stone masses come from the heater data on this site: compact continuous stoves take 20–40 kg, large ones such as the HUUM Hive Wood up to 130 kg; Narvi's Aito heat-storing stoves take 60–380 kg depending on model and stone type.

Why many Finns think these are the best

In a continuous sauna the stones are small and are being heated while you bathe. In a heat-storing stove or smoke sauna the fire is out. A large, deeply heated stone mass releases steam evenly ladle after ladle, without the stones cooling down after a few throws, and there is no fire drawing air through the room. Bathers describe the löyly as soft, full and long, and Narvi markets its Aito stoves on exactly that.

This site was made by a Finn who considers the smoke sauna and the heat-storing sauna the best saunas there are. The calculator stays brand-neutral; this is the one place where we say what we prefer.

The heat-storing stove

A heat-storing stove, often called a once-heated stove, has a firebox under a large chamber of stones inside an insulated, closed casing with a lid. You light it well before the sauna, let the stone mass heat right through, and let the fire burn out. When you bathe, you open the lid to the hot stones and throw löyly; between rounds the lid keeps the heat in. One firing lasts for hours, and Narvi says the heat can last until the next morning.

Because there is no flame during bathing, the stove gives the experience closest to a smoke sauna while still having a chimney and needing no settling time.

Sizes

ModelRoomStones
Narvi Aito AK-478–12 m³
283–424 ft³		60 kg ceramic
90 kg olivine
Narvi Aito AK-579–20 m³
318–706 ft³		90 kg ceramic
160 kg olivine
Narvi Aito AK-57K11–23 m³
388–812 ft³		130 kg ceramic
220 kg olivine
Narvi Aito 6814–26 m³
494–918 ft³		200 kg ceramic
290 kg olivine
Narvi Aito 7819–30 m³
671–1059 ft³		240 kg ceramic
380 kg olivine

Wood-burning mode in the calculator lists these stoves when your calculated room volume fits their range.

Things to plan for

  • Weight. Hundreds of kilograms of stones plus the stove body. Check that the floor can carry it.
  • Room size. The models are made for medium and large rooms; the smallest Aito starts at 8 m³ (283 ft³).
  • Heating ahead. You start well before bathing, so it suits a planned sauna evening rather than a quick one.
  • Chimney and clearances as for any wood stove; the stove manual gives the distances.

The smoke sauna

The smoke sauna is the oldest kind: a log room with a large stove of stones and no chimney. While the fire burns, smoke fills the upper part of the room and seeps out slowly through a small hatch in the wall or roof. When the stones are hot, the fire is allowed to die, the embers are cleared and the room is aired. What is left is a dark, soot-blackened room with a scent of smoke and some of the softest löyly anywhere.

Finnish sauna culture was added to UNESCO's list of intangible cultural heritage in 2020, with the smoke sauna named among its forms. The smoke sauna tradition of Võromaa in Estonia was listed separately in 2014.

How a smoke sauna is heated

Practice varies from sauna to sauna, but these points come from the Finnish Sauna Society's guidance for chimneyless saunas:

  1. Dry, small wood. Split pieces of about 2–5 cm. Alder and aspen burn clean and contain no pitch; a little pine or spruce adds a bitter note to the scent.
  2. Low, steady heat. Keep the room at about 60–80 °C during heating. An overheated smoke sauna is spoiled.
  3. Let the smoke out slowly. The hatch should let smoke drift out without a draught. Aim to keep the smoke layer above bench height so the lower benches stay clean.
  4. Small final loads. Use the smallest pieces last; alder or aspen at the end helps burn the firebox clean.
  5. Settle for at least an hour. Let the embers go out and the smoke clear, then remove remaining charcoal and ash before anyone goes in.

One smoke sauna owner interviewed by Sauna Times heats for about four to six hours depending on the weather and how long the evening will be.

Carbon monoxide. Burning wood in a closed room produces carbon monoxide, which you cannot see or smell. According to the Finnish Sauna Society it peaks when the fire is lit and each time wood is added, rises if you close the hatch to smother the embers, and rises again if you throw water while embers remain. Nobody bathes until the embers are out, removed and the room has been aired. A carbon monoxide alarm in the dressing room is a sensible addition.

Things to plan for

  • A separate building. Smoke saunas are built as standalone log saunas, with fire safety as a central part of the design.
  • Local rules. Check building and fire regulations and your insurer before building. Outside the Nordic countries few builders have experience with them, so look for one who does.
  • Time. Heating takes most of an afternoon, so a smoke sauna suits weekends and special occasions; many households also have a quicker sauna for everyday use.

Sources