Below you can find a recommendation for the sizing of bathroom extractor fans based on the size of the room.

The calculator is based on intermittent operation. This means a mechanical fan that does not run 24 hours a day, but only operates via switch or sensor control.

The capacity of all fans can be seen in the fan selector or under the individual product.

How large a fan should I choose?

When choosing an extractor fan for a bathroom, toilet or utility room, it is important to select a model with sufficient capacity. A fan that is too small for the room may struggle to remove moisture and stale air quickly enough, whereas a correctly sized fan ensures a more efficient air change.

Men How powerful does an extractor fan need to be, and how many m³/h should it be able to move?

That depends, among other things, on the size of the room, the ceiling height and how much moisture is normally generated in the room. Here on the page, you can calculate which capacity suits your room based on the number of square metres.

Fan size based on m²

When talking about the size of a fan, it is normally not about the fan's physical dimensions, but about its capacity measured in m³/h.

The capacity indicates how many cubic metres of air the fan can move in an hour.

A bathroom of, for example, 5 m² therefore does not necessarily require the same extractor fan as a bathroom of 12 m². The larger the room, the greater the volume of air the fan must generally be able to handle to achieve the same number of air changes.

Our calculator is based on a standard ceiling height of 2.4 metres and calculates the recommended capacity range based on the size of the room.

How many air changes per hour should there be?

A good way to size a fan is to look at how many times the air in the room is replaced in an hour.

The requirement depends in particular on whether there is a bath or shower in the room.

Room with bath or shower:
As a starting point, we recommend 4–10 air changes per hour.

Room without bath or shower:
Here will 2–6 air changes per hour typically be a suitable starting point.

In a bathroom with a shower, large amounts of moisture are produced in a short time. Therefore, the need for ventilation is significantly greater than, for example, in a toilet without a bath.

How to calculate the fan's capacity

First, the room's volume is calculated:

The room's area in m² × the room height = the room's volume in m³

Then the volume of the room is multiplied by the desired number of air changes per hour.

Do you, for example, have a bathroom on 8 m² with a ceiling height of 2.4 metres, has a volume of:

8 × 2.4 = 19.2 m³

If you want between 4 and 10 air changes per hour, this corresponds to a fan capacity of approximately:

77–192 m³/h

This does not necessarily mean that the fan has to run constantly at maximum capacity. Many modern bathroom extractor fans can regulate their speed and, for example, increase ventilation automatically when the humidity rises.

What capacity bathroom extractor fan should I choose?

It can be tempting simply to choose the most powerful fan, but high capacity is not always the only thing that should determine the choice.

You should also consider:

• noise level
• humidity control
• continuous ventilation
• multiple speed settings
• diameter and length of the canal
• resistance in the ventilation duct
• the location of the fan

The maximum capacity stated for a fan is therefore only part of the assessment. Long ducts, bends and other resistances can reduce the actual air volume.

Extractor fan for bathroom, utility room and toilet

The need for ventilation varies from room to room.

In a bathroom with bath or shower the extractor fan should be able to handle the large amount of moisture that occurs during and after the bath.

In a toilet without a shower is the moisture load normally lower, and the need for air exchange will therefore typically also be less.

In a utility room does the need depend, amongst other things, on whether there is a floor drain, washing machine, tumble dryer or other installations that can contribute to moisture.

Therefore, the extractor fan should always be chosen based on the specific room rather than solely on the duct diameter or the physical size of the fan.

Calculate which extractor fan you should use

Are you in doubt whether, how big a fan you need for your bathroom, you can use the calculator on this page.

First, choose whether the room has a bath or a shower, and then enter the room size in m². The calculator will then display a recommended capacity range in m³/h.

The calculation is based on a room height of 2.4 metres and gives you a good starting point for finding a fan with the right capacity.

Once you know the required air volume, you can use our fan selector or see the capacity under each individual product to find a fan that suits your room.

The right ventilation provides a better indoor climate

Correct ventilation sizing helps to remove humid air, odours and excess moisture from the room. This is especially important in bathrooms and other rooms where large amounts of moisture are regularly generated.

With the right extractor fan, you therefore not only get a fan that suits the size of the room – you also get better conditions for a healthy and comfortable indoor climate.