The installation of the Harvia M3 SL should always be planned carefully and carried out strictly according to the manufacturer's installation and operating instructions. The stove is designed for sauna rooms with a volume between 6 and 13 m³. However, when calculating the required heating capacity, all uninsulated surfaces such as glass, concrete, brick, stone or tiled walls must be taken into consideration. Harvia specifies that approximately 1.2 m³ of additional sauna volume should be added for every square meter of uninsulated surface. For solid log structures, the calculated sauna volume should be multiplied by a factor of 1.5.
Before the stove is used inside the sauna for the first time, Harvia strongly recommends performing an initial firing outdoors. During this process, the protective coating on the stove may produce smoke and odors while curing. No sauna stones should be placed in the stove during this initial firing. Only after the stove has completely cooled down may the stones be installed.
For proper operation, only suitable sauna stones measuring 10–15 cm should be used. Before installation, the stones should be cleaned of dust and carefully stacked so that larger stones are positioned at the bottom and smaller stones at the top. Adequate spacing between stones is essential to allow proper airflow through the stone chamber.
Fuel quality plays a major role in performance and durability. Only dry firewood should be burned. The maximum recommended log length is 35 cm with a typical wood diameter of approximately 8–15 cm. Materials such as particle board, painted wood, impregnated wood, plastics, coal, pellets, waste materials, garden waste or other unsuitable fuels must never be used. Improper fuels can damage the stove, reduce efficiency and create safety hazards.
Prior to each firing, the ash drawer should be emptied to ensure sufficient combustion air. The firebox door should remain closed during normal operation. Excessive chimney draft can cause overheating of the stove body and may significantly shorten the service life of the appliance. Maintaining proper combustion conditions is therefore essential for safe and efficient operation.
The floor structure must safely support the weight of the stove and stone load. On combustible floors, suitable floor protection measures must be installed. For SL models, the area in front of the external loading door must be protected by non-combustible materials. Harvia specifies a spark protection area of at least 450 x 800 mm in front of the firebox opening.
Ventilation planning is equally important. The fresh air supply should typically have a diameter of 50–100 mm. Exhaust air should be located close to the floor and positioned as far from the stove as possible. With mechanical ventilation systems, fresh air should enter above the stove, while with natural ventilation it should enter below or beside the stove. The flue gas connection uses a 115 mm diameter flue pipe and must be connected to a suitable chimney or compatible Harvia steel chimney system. All connections should be professionally sealed and installed using approved fire-resistant materials.
Regular maintenance is necessary for long-term reliability. Ash should be removed regularly, smoke channels cleaned periodically and the chimney maintained according to local regulations. Sauna stones are subject to thermal wear and should be inspected, restacked and replaced when necessary at least once per year. For sauna infusions, only clean household water should be used, and water should always be poured onto the stones rather than directly onto hot steel surfaces.
