Which size and shape fits your heater.

Two real choices on this page: size and shape. Size first - the 4-6 inch stones suit larger heaters with bigger stone cavities, which is most of the lineup we carry. The HUUM Drop, HUUM Hive Mini, Homecraft Revive, Homecraft Apex, and the Narvi Kaamos, NC, Inari, and Leisurecraft TimberGlow wood-burners all hold the larger 4-6 inch stones comfortably. The 2-4 inch stones are sized for the smaller heaters - the Homecraft Revive Slim with its narrower frame, the Narvi Kuru, and the smaller Narvi wood stoves - where the larger rocks won't stack properly in the cavity.

Shape is the second decision. The 4-6 inch Wellendi sauna rocks and 2-4 inch Wellendi sauna rocks are quarried and angular, with rough split faces that lock together when stacked - that's good for airflow between the stones and consistent heat retention session after session. The HUUM sauna stones are rounded and river-tumbled, smoother to handle and easier to arrange, which gives a slightly softer, slower steam release. Both work; it's a feel-and-look preference more than a performance difference.

How many boxes you'll need.

Each Wellendi or HUUM box is 20 kg (44 lbs). Match to your heater's published stone capacity:

Heater	Stone capacity	Boxes needed
HUUM Drop	55 kg	3 boxes
HUUM Hive Mini	170 kg	9 boxes
Homecraft Revive	200 lbs (~91 kg)	5 boxes
Homecraft Revive Slim	100 lbs (~45 kg)	3 boxes
Homecraft Apex	310 lbs (~141 kg)	7 boxes
Narvi Kaamos / NC	60 kg	3 boxes
Leisurecraft TimberGlow	200 lbs (~91 kg)	5 boxes

Each product page lists exact stone capacity. Round up rather than down - a partially filled heater cavity reduces steam quality and forces the elements to work harder.

Why olivine diabase, and why from Lake Huron.

Olivine diabase is an igneous rock with three properties that matter for sauna use: high heat retention, low porosity, and high thermal stability. In plain terms, it holds temperature longer between water throws, resists cracking when you pour cold water on hot stones, and handles years of repeated heat-cool cycles without breaking down. Most generic landscape rock sold as "sauna stones" hasn't been tested for any of that and tends to crack within months of regular use. Our Wellendi rocks are quarried in Ontario from a Lake Huron source, so they ship from Canada and we know exactly where they came from.

Frequently Asked Questions:

Can I use any rocks in my sauna heater, or do they have to be sauna-specific stones?

They have to be sauna-specific stones. River rocks, beach stones, and most landscape rock will crack or split when heated to sauna temperatures and doused with water - in some cases violently enough to damage your heater or hurt someone. The rocks have to be a dense igneous stone like olivine diabase or peridotite, with low porosity and high thermal stability. Hardware store landscape stones aren't tested for sauna use; we don't recommend them.

Should I rinse new sauna rocks before using them?

Yes - always rinse them before the first use. Quarried and tumbled stones come with rock dust on the surface, and that dust ends up burning off in your sauna on the first heat-up if you skip the rinse - producing a dusty smell and visible particulate in the room. Rinse each stone under cold water until it runs clear, then stack them loosely in the heater with airflow between stones. Don't rinse hot stones already in the heater; that's how cracks happen.

What's the difference between rounded sauna stones and split-faced rough stones?

Steam release and feel. Split-faced rocks like the Wellendi olivine diabase are quarried and angular - rough surfaces lock together when you stack them, which gives sharper, more immediate steam when water hits them. Rounded rocks like the HUUM sauna stones are river-tumbled smooth - they pack more closely and release steam more gradually, which produces a softer, slower loyly. Neither is objectively better; it's a matter of how you like the steam.

Do I need different sauna rocks for electric vs wood-burning heaters?

No - the same olivine diabase works in both. Electric heaters and wood-burning stoves heat the rocks to similar temperatures and put the same demands on the stone material. What changes is the size and quantity that fits your specific heater's stone cavity. Wellendi and HUUM stones are compatible with HUUM, Harvia, Homecraft, Narvi, Leisurecraft, and any other sauna heater that takes loose stones.

How often should I replace my sauna rocks?

Every 2-4 years for typical home use, every 1-2 years for heavy or commercial use. Inspect them every 6 months - look for visible cracks, stones breaking down into smaller pieces, or excessive dust in the heater cavity. Worn-out stones restrict airflow, reduce steam quality, and make the heater work harder, which shortens element life on electric heaters. When the rocks start crumbling or you notice weaker steam, it's time to replace the load.

Huum Sauna Stones

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