You need to make many important decisions when constructing a sauna. Among other things, you must choose a proper sauna heater. Once you have decided whether you desire an electric sauna heater or a wood burning sauna stove (or even both!), the next step is to determine the capacity of a suitable sauna heater. This means that you have to calculate the power rating of the sauna heater that is suitable for your steam room and enables you to prevent excessive heating or insufficient temperatures. Our everyday work proves that people tend to underestimate matters concerning the capacity of the sauna heater.

It is important to remember that **a more powerful heater does not necessarily provide better steam**. Saunas are different, and the characteristics of the steam room must be taken into consideration when choosing the heater.

All massive wall surfaces of the sauna where heat accumulates should be insulated for utilizing the optimum capacity of the heater. When this is not possible, a higher power rating is necessary to ensure that the heater warms up the non-insulated surfaces (e.g., glass doors or log walls) and compensates for the heat loss. Therefore, heater selection cannot only be based on the size of the steam room, and the calculated cubic size V_{A} must also be considered.

#### This article explains:

- the calculation formula that enables one to determine the capacity of a suitable sauna heater
- most important considerations that apply to selecting a proper heater

Sauna calculator is a useful tool that assists you with calculations and helps to choose the power rating and model of the heater that suits your sauna. HUUM sauna calculator is available here:

#### What are the criteria for adequate insulation?

The following sauna wall and ceiling construction is considered to be sufficiently insulated:

- carefully installed insulation layer of 100 mm (minimum 50 mm);
- moisture barrier of the construction is established with taped aluminum foil or another reflective material;
- there is at least a 10 mm air gap between the moisture barrier and the clapboard;
- a light wooden board with an approximate thickness of 12–16 mm has been used for interior finishing;
- there is at least a 5 mm air gap on the boundary of the ceiling panels at the upper part of the wall boards.

In order to optimize the capacity of the sauna heater, it would be beneficial to make the ceiling of the sauna lower, which reduces the cubic size of the steam room (normal height of the sauna is 2100–2300 mm, minimum height is 2000 mm). Insulation of the ceiling must be at least 100 mm thick, and the ceiling should be lined as described above.

Calculated cubic size of the steam room (V_{A}) is calculated by adding the additional volume of non-insulated surfaces (V_{S}) to the cubic meters of the room (V_{R}). One square meter of non-insulated surface equals 1.2–1.5 cubic meters, depending on the material. A glass door or a glass wall absorbs less energy than a non-insulated wood or log wall. In order to determine the additional volume of non-insulated surfaces (V_{S}), multiply the square meters of non-insulated surfaces (S) by the corresponding coefficient (k).

## Non-insulated surface |
## Coefficient (k) |

Glass | 1,5 |

Log wall or other non-insulated surface | 1,5 |

For obtaining the actual cubic size of the steam room (V_{R}), multiply its length (a) by width (b) and height (h).

**V _{R} = a x b x h**

In order to determine the square meters of non-insulated surfaces (S), multiply the edges of the non-insulated surface plane.

**S = a x b**

Then multiply the square meters of non-insulated surfaces (S) by the coefficient (k) that depends on the material of the non-insulated surface. This gives you the additional volume of non-insulated surfaces (V_{S}).

**V _{S} = S x k**

In order to obtain the calculated cubic size of the steam room (V_{A}), add the additional volume of non-insulated surfaces (V_{S}) to the actual cubic size of the room (V_{R}).

**V _{A} = V_{R} + V_{S}**

**One calculated cubic meter presumes one kilowatt of the heater’s power. **Choose a sauna heater that has the closest capacity.

**1 m ^{3} _{A} = 1 kW**

**For example**, if your steam room is 2 meters long, 1.5 meters wide and 2.3 meters high,

you’ll get the cubic size of the room by multiplying these figures.

**VR = 2 x 1.5 x 2.3 = 6.9 m3**

Let’s presume that the steam room has a glass surface (a glass wall with a door) that is 1.5 meters wide and 2.3 meters high.

Square meters of the non-insulated surface are determined as follows:

**S = 1.5 x 2.3 = 3.45 m2**

We must multiply this result by the corresponding coefficient (1.5).

**VS = 3.45 x 1.5 = 5.18 m3**

Finally, we should add the additional volume of non-insulated surfaces to the actual cubic size of the room, in order to obtain the calculated cubic size of the steam room.

**VA = 6.9 + 5.8 = 12.08 m3**

You should choose the sauna heater on the basis of the calculated cubic size 12.08 m3, and not the actual cubic size 6.9 m3.

Considering the calculations above, HUUM **DROP sauna heater** with the power rating of 9 W would be appropriate for this particular sauna.

As you can see, non-insulated surfaces have a significant impact on suitable heater options. Non-insulated surfaces account for nearly 40% of the required capacity.

After the calculations, compare the results with the specifications of the heater manufacturer, when you start choosing the sauna stove that matches the calculated cubic size of the steam room. It is reasonable to add some reserve, as it is not recommended to heat the sauna stove constantly at full power. Unlike electric sauna heaters, a wood burning stove enables one to vary the heating power. Constant intensive heating shortens the useful life of the stove remarkably. When the sauna reaches the desired temperature, just a few logs should be used for keeping the furnace hot.

At the same time, the wood burning stove should not be excessively powerful. If the stove is too powerful, the room heats up quickly, but sauna rocks are not hot enough for adding steam. In the case that you continue heating, the steam room will be overheated by the time the sauna rocks obtain the sufficient temperature.

Before deciding on a particular electric sauna heater model, an electrician should determine the parameters of the main circuit breaker and the cross-section of the power cable. **In the case that your power system does not enable you to mount a heater that has the required capacity, opt for a heater that holds more sauna stones.** A larger amount of stones stores more energy and vaporizes more water, and hence compensates for the output shortage of the sauna heater. Heating the sauna takes more time, but ensures a more satisfactory sauna experience.

Determining the proper capacity of the sauna heater is an important part of building a sauna. Excellence of sauna sessions depends on a variety of factors. One significant, yet often neglected aspect is ventilation. Learn more about **sauna ventilation**.