How many sauna stones do I need? Types, amounts and stacking

Stones are the part of a sauna you actually feel. They store the heat, they turn a ladle of water into steam, and they shield the room from the heater’s elements. Most heaters ship without them. HUUM, for example, lists stones as a separate purchase for its DROP heater.

Stone amounts by heater

These are the makers’ own figures. Always check the manual for your exact model.

Working out boxes: divide the stone weight by the box weight and round up. A HUUM DROP needs about 55 kg, and 55 ÷ 15 = 3.7, so order 4 boxes (60 kg). Our advice: a few spare kilograms let you skip badly shaped stones and replace cracked ones later.

Which stones to use

Suitable. Harvia names peridotite, olivine and olivine diabase, and its KIP manual adds vulcanite. HUUM asks for natural stones sold specifically for sauna heaters, such as olivine diabase or olivine. Harvia’s advice is that heater stones should be heavy, dark and large enough to store plenty of heat.

Not suitable. Harvia says ceramic “stones” and soft soapstone must not be used, and that rocks collected in nature aren’t suitable. Homecraft also rules out soapstone, lava stone and structural clay tiles. HUUM’s DROP manual says not to use decorative stones, because they don’t store enough heat and break easily.

Round or split-faced? Split-faced (angular) stones are the traditional choice. HUUM recommends rounded stones, which it says give milder steam. Some heaters need one type: Harvia’s Cilindro manual calls for angular split-face stones, while Harvia says its Spirit heater requires round stones.

Size. Most heaters take 5–10 cm stones. HUUM’s CLIFF and STEEL take smaller 3–5 cm stones that fit between their elements. Homecraft’s Revive manual asks for rocks of about 2–5 in. Large wood stoves may call for 10–15 cm stones.

White and polished decorative stones look good on top of a heater. Use them only where your heater’s manual allows it.

Check your warranty before you buy stones

Stone rules are warranty rules:

• Harvia: the KIP manual says to use only Harvia sauna heater stones, and the Cilindro manual excludes defects caused by decorative stones or stones Harvia doesn’t recommend.
• Homecraft: the Revive manual says rocks not sourced or provided by Homecraft void the heater warranty.
• HUUM: defects caused by unsuitable stones aren’t covered by the warranty.

That applies to stones from any seller, including us. We stock HUUM’s own rounded olivine diabase stones in the two sizes HUUM specifies (3–5 cm and 5–10 cm, in 15 kg boxes), Narvi’s split-face olivine diabase in 5–10 cm and 10–15 cm (20 kg boxes), and white stones and polished jadeite, which are mostly used as a decorative top layer. We don’t sell Harvia or Homecraft stones by the box, so if your Harvia or Homecraft manual calls for the maker’s own stones, use those to keep your warranty intact. Tell us your heater model and we’ll check what its manual asks for.

How to stack sauna stones

1. Switch the heater off at the breaker and let it cool. Wear gloves.
2. Rinse the dust off the stones. Harvia, HUUM and Homecraft all say to do this first.
3. Place stones one at a time. Never drop or pour them into the heater.
4. Support the elements without forcing them. Place stones around and between the elements so they stay straight. Don’t wedge stones between them or bend them.
5. Leave room for air. Stones packed too tightly block airflow. HUUM asks for a tight outer layer with space for air inside, and Homecraft asks for sparse piling.
6. Cover the elements completely. No element should be visible. Harvia warns that bare elements can cause a fire hazard, and HUUM says a too-sparsely filled stone space is a fire hazard.
7. Don’t build a tall pile on top. Harvia says not to stack stones too high.

Where the manuals differ: Harvia’s current KIP manual starts with flat stones at the bottom and puts larger stones on top. HUUM’s DROP manual puts bigger stones at the bottom and sides, and Homecraft keeps the smaller rocks for the top 9 inches. Follow the manual for your model.

Looking after your stones

Stones crack and crumble with repeated heating.

• Harvia (KIP): inspect at least once a year, clear out debris, replace broken stones, and replace all stones every two years, or sooner with heavy use.
• HUUM (DROP): check after 100 hours of use or yearly, rearrange after 200 hours and replace any cracked stones, then replace them all after 400 hours.
• Homecraft (Revive): review the rocks after 12 months and replace worn or broken ones.

Next steps

• Shop sauna stones by size and box weight.
• Still choosing a heater? Start with our heater size guide or browse sauna heaters.
• Add guards, flanges and other parts from heater accessories. You pay nothing until you approve a written invoice.