The first heating of the sauna heater removes residual protective and processing substances from different manufacturing phases. These substances may cause unpleasant odour and even smoke in some cases, and it is therefore important to have the sauna well ventilated during the initial heating. Because of the odour it is not recommended to go to the sauna during the initial heating.
Note also that in case any such repair work has been carried out anywhere in the flat that has required the use of paint, varnish, glue or other substances that contain evaporable components (solvent vapours), even small amounts of such materials will cause a strong petrol-like odour as the vapour passes through between the hot rocks and resistors of the sauna heater. The odour wears off when the solvents in the flat have completely dried out.
Heating the sauna heater might furthermore emphasise other odours mixed in the air that are not, however, caused by the sauna or the heater. Onion and other strong seasoning used in cooking are some of these odours. Also, odours from the garage or a near-by oil filler neck may mix into the incoming air of the sauna and be detected when going to the sauna.