The secret to a good sauna is a well-planned ventilation solution. Unfortunately, the significance of the air exchange system and its planning are often underestimated in a sauna building. Having oxygen-rich air in the sauna is yet just as important as the capacity of the sauna heater, the quantity of sauna stones or the width and height of the sauna bench. Improper air circulation of the steam room results in a lack of air and discomfort. Air of the room stratifies if the ventilation system is not constructed properly, and the temperature at the lower stages of the sauna bench drops.
Layered air due to badly planned ventilation is one of the most typical mistakes in sauna construction.
The type and construction of the ventilation system depends on which kind of stove you have. So, make sure you think about ventilation when choosing a stove for your sauna.
A typical ventilation system is made up of three parts (sometimes two):
- supply air pipe
- exhaust air pipe
- drying pipe
Your ventilation solution depends on whether the room has gravity-based ventilation or mechanical ventilation. In general, the supply air pipe should be positioned close to the stove at the proper height, so that the incoming colder air reaches the heat of the stove, heats up, and creates circulation in the room.
Choice of ventilation system depends on the stove type
Air circulation in the steam room must correspond to the particular stove. Electric stoves require a different ventilation solution than stoves that use wood. You must also consider whether the stove door (stove hearth) is inside the steam room or the stove is filled from outside the steam room.
The construction of the stove also plays a role. When planning your ventilation, it is important to know the difference between closed-sided stoves and open or net-stoves.
In case of closed-sided stoves
- the air circulates from bottom to top and the stones are placed on top of the stove. A very common mistake is placing the supply air pipe in the middle of the closed-sided stove where there is no air access. In this case, the incoming air is not heated properly and sufficient air circulation will not occur. And it does not matter whether your closed-sided stove is electric or wood-heated. The incoming air should be directed underneath the stove or above the stove, according to the particularities of the sauna and the stove. See below for concrete cases
In case of a net-stove
- the sides are open and the stones are situated inside a massive net with plenty of air access from all sides, the supply air pipe should be placed in the middle of the stove. This directs air to the centre of the stove where it will be heated and lifted to create air circulation in the room.
All saunas must have a drying pipe. As its name suggests, this pipe is used for drying the sauna after use. This can be opened if the sauna has too much moisture or lacks sufficient oxygen. If possible, though, the drying pipe should be left for drying the sauna, not for fixing other problems. The drying pipe should be closed during the sauna session because the heat in the room may get layered and leave your feet cold. The drying pipe should be located away from the heat source, in the ceiling or high on the wall.
Mechanical ventilation systems are alike for electric stoves and stoves that are heated from the antechamber (i.e. no hearth door in the steam room). Wood-fired stoves fed from the steam room however require special attention.
Saunas with closed-sided stoves may use two different supply air pipe solutions. One option is to construct the supply air pipe directly above the stove (no lower than 31 in / 80 cm from the floor). In this case, the incoming cold air will fall onto the heated stove, heats up, and creates air circulation. The other option is to direct the incoming air below the stove where it is sucked into the hot stove.
In the case of net-stoves, the incoming air should be directed to into middle section of the stove (but no lower than 16 in / 40 cm from the floor).
It does not matter whether you have a closed-sided stove or a net-stove, if it uses wood for heating the supply air pipe must be on the opposite side of the hearth door. If the supply air pipe is close to the hearth door it will exit through the hearth without entering air circulation.
If the wood-fired sauna has mechanical ventilation, it requires extra oxygen for burning.
To that end, one should build an additional heating supply air pipe close to the hearth. Please consult the cross-section of the air inlet provided by the stove manufacturer.
The exhaust air pipe should be constructed to the opposite wall from the stove. It should be no more than 24 in / 60 cm from the floor, just behind your feet. However, since the air is circulated mechanically its height is not too important — the exhaust air pipe can also be below the supply air pipe.
Installing mechanical ventilation requires a professional
It is recommended to consult a professional when planning, installing or adjusting the mechanical ventilation system. If installed or maintained improperly, a mechanical ventilation system with a wood heater may cause low air pressure and generate dangerous levels of carbon monoxide (CO). Mechanical ventilation systems may be installed in different ways. The entire ventilation system of a building must function as one.
It does not matter whether using an electric stove or a wood-fired stove filled from the antechamber, the logic of the gravity-based ventilation is the same. Having a wood-fired stove filled from the steam room, however, the gravity-based ventilation follows a different logic.
Electric stove or wood-fired stove in the antechamber
In case of a closed-sided stove with gravity-based ventilation, the supply air pipe should be constructed close to the floor, at the height where air can access the stove from below, heats up, and generate air circulation. The other option is to construct the supply air pipe just above the stove (no lower than 31 in / 80 cm from the floor).
In case of a net-stove, however, the supply air pipe should be constructed roughly in the middle of the stove (no higher than 16 in / 40 cm from the floor).
Stove with hearth door in the steam room
Using an ordinary closed-sided stove, the supply air pipe should be constructed at the height of the lower air circulation zone. It is important to note that the supply air pipe must be on the opposite side of the stove from the hearth door—otherwise, the incoming air will exit the steam room without generating circulation. The other option is to construct the supply air pipe just above the stove.
In case of a net-stove, the supply air pipe should be constructed in the middle of the stove or higher (no lower than 16 in / 40 cm from the floor).
With an electric stove or wood-heated stove filled from the antechamber, the exhaust pipe should be constructed to the opposite wall of the steam room. It should be at least 8 in / 20 cm higher than the supply air pipe, but not higher than 24 in / 60 cm from the floor.
Stove with hearth door in the steam room does not require a separate exhaust pipe as the stove itself acts as an exhaust.
The importance of good ventilation in the sauna room cannot be overstated. You may have experienced the difficulty of breathing in a poorly ventilated room, where oxygen levels are low and dizziness sets in. The heat can also be tiring on the body. Therefore, it is crucial to have a steady supply of fresh air to ensure that the sauna experience is invigorating rather than exhausting. It is important to consider ventilation when choosing a heating stove, as the type of heater and the ventilation of the entire building must be taken into account to ensure proper air exchange. With so many options available, it can be overwhelming to make the right choice. If you’re uncertain, don’t hesitate to seek the advice of an expert.
Picture: Aire X Sauna by Heartwood Saunas www.heartwoodsaunas.com
Based on: Hõbepappel, Urmas; Hõbepappel, Liisa; Nellis, Silja; Nellis, Siim. Suur sauna raamat. Tartu, (manuscript)