Harvia KIP80B 8 kW 240VAC
Harvia · electric · 8 kW · rated for 251–424 ft³ (about 7.1–12 m³, our conversion)
Sauna stones
Use the stone types your heater's maker lists, never stones gathered outdoors or decorative ones, and rearrange them at least once a year, replacing any that crack.
Which stones
Harvia lists peridotite, olivine and olivine diabase as suitable heater-stone materials, and says stones gathered from nature are not suitable. Harvia says ceramic "stones" and soft soapstone must not be used because they store too little heat and can make the heater overheat.
HUUM says decorative stones should not be used because they store too little heat and break easily.
What size
Harvia says smaller 5–10 cm stones are usually used in electric heaters because they fit between the elements.
Harvia's Linear 18 Compact wood-stove manual calls for 10–15 cm stones and lists peridotite, olivine diabase, olivine and vulcanite.
Rearranging and replacing
Harvia says stones slowly break down with use, and advises rearranging them at least once a year, more often with frequent use. Harvia suggests knocking stones together when rearranging; ones that crack or sound hollow should be replaced. Harvia says stones that crumble or are discoloured should be discarded, and stones should be washed and dried before restacking. (Harvia)
HUUM's DROP manual says to rearrange the stones after 200 hours of use and replace any that have cracked.
Examples on Saunakivi
HUUM DROP 9
HUUM · electric · 9 kW · rated for 8–13 m³ (about 283–459 ft³, our conversion)
HUUM HIVE 15
HUUM · electric · 15 kW
Kuuma Low Profile (Medium)
Kuuma · wood-burning · rated for 448–700 ft³ (about 12.7–19.8 m³, our conversion)
Questions
Can I use stones from my garden in a sauna heater?
Harvia lists peridotite, olivine and olivine diabase as suitable heater-stone materials, and says stones gathered from nature are not suitable.
How often should sauna stones be replaced?
Harvia says stones slowly break down with use, and advises rearranging them at least once a year, more often with frequent use. HUUM's DROP manual says to rearrange the stones after 200 hours of use and replace any that have cracked.
Sources: H1001L08_v8_DROP_2.0_User_Manual_US_PRINT.pdf; Harvia sauna heater stones