Maintaining the sauna heater and sauna stones

Short answer: maintaining a sauna heater comes down to three things: the sauna stones (check annually, restack loosely, replace crumbling stones), the airways (keep the ventilation inlet low near the heater and the outlet high on the opposite wall open, and sweep the chimney annually with wood firing) and clean loyly (only water, optionally with a few drops of sauna fragrance, never pure oil). Keeping up with this preserves the soft, deep heat the sauna was bought for.

The sauna stones: the heart of the heat

The stones store the heat and release it as gentle radiant warmth and loyly steam. Here is how to keep them in condition:

1. When installing: rinse new stones to remove stone dust and stack them loosely so air can circulate between them. Stones packed too tightly smother the heater.
2. Annually: take the stones out, remove grit and fragments, replace stones that are crumbling or feel dull and saturated, and restack everything loosely.
3. Signs of wear: flat, stuffy heat, weak steam when pouring water on the stones and grit at the bottom of the heater.
4. Pouring water: use clean water, optionally with a few drops of sauna fragrance. Never pure (essential) oil on the stones: it can splash, catch fire and leave deposits on the stones.

Good to know when replacing a heater: its power is calculated based on the cabin, using a rule of thumb of 1 kW per m³ of volume, with surcharges for outdoor placement (factor 1.2 to 1.5) and glass (around 1 to 1.5 m³ extra per m² of glass). If in doubt, choose a size larger; an undersized heater runs continuously at full power and barely reaches the target temperature.

Wood-fired heater

• Fire properly: dry, split wood with less than 20 percent moisture; never painted, treated or wet wood. The air damper is your throttle.
• Ash: remove the ash once it is completely cold and keep the grate clear.
• Chimney: have the flue swept annually. Deposits reduce draught (slow heating, smoke blowing back) and are a fire risk.
• Spark arrestor: mandatory in wind, dry conditions and near overhanging vegetation.
• Outdoor check: every autumn, inspect the rain cap, heat shield and duct for rust, loose parts and leaks.

Electric heater

• Connection: its own separately fused 400V circuit with a residual current device, installed by a certified installer. Doing three-phase electrical work yourself is not an option.
• Seasonal check: before the heating season, inspect the heating elements (no visible damage or sagging coils), the controls and the sensors. If in doubt, have it inspected rather than keep using it.
• Remote control: if your heater has an app or timer, test that setting calmly during the day, not on the evening guests arrive.
• Maintenance: virtually none beyond that; the stones remain the annual task here too.

The cabin's airways

A sauna needs to breathe: the air inlet sits low near the heater, the outlet high on the opposite wall. Keep both open and free of towels or items. A closed-off ventilation system feels warmer at first, but leads to stuffy air within a session and, over time, moisture and wood problems. How to look after the cabin itself is described in outdoor sauna use and maintenance.

Maintenance calendar