bathroom exhaust fan

How to Choose the Right Exhaust Fan

Exhaust fans are an essential part of any home where moisture and steam can be found, and mildew or mould could grow. And honestly, try cooking a steak inside without setting off the mandatory smoke alarm. And who wants to put up with foggy mirrors or the awful smell lingering in the toilet?

But when it comes to choosing the right exhaust fan, what should you even look for?

There are two main things to consider. One is noise and the other is the extraction value or the rate of airflow. The greater the rate of airflow, the noisier the fan is liable to be. It’s also the case that the quieter exhaust fans are more expensive. But first, you should work out how powerful the fan should be.

Calculating Exhaust Fan Capacity

In terms of desired exhaust fan output capacity, it all comes down to how many times the air in the room needs to be replaced. For areas that really steam up, such as the kitchen and the bathroom, we recommend that all of the air in the room should be replaced 20 times in an hour. The figure that you will see tells you how many cubic metres of air per hour (m³/h) the fan extracts. So how do you know what figure suits your room? You need to know how many cubic metres your room is. That’s an easy calculation – it’s just length x width x height.

So if your bathroom is 3m long x 2m wide x 2m high, then it’s 12 cubic metres. That amount of air should turn over 20 times if it’s a steamy bathroom, so multiply 12 by 20. The result is 240 m³/h and that’s the lowest figure you should get for the fan. Fans for toilets don’t need to be so powerful because you only need to change the air in the room around 10 times an hour.

Types of Exhaust Fans

The type of exhaust fan you will choose depends on the nature of the room. A ground floor kitchen might only be able to accommodate a wall or a window exhaust fan. A plain ceiling exhaust fan does the job very well in most cases, with the unwanted air simply expelled into the roof space.

 

This is not a problem if you have enough well ventilated roof space, but sometimes it is necessary to use a duct to vent the air into the outside atmosphere through a flue. That’s where you can use an inline exhaust fan, which sits above a ceiling or wall vent and sucks air through a duct. Because the inline fan is not directly on the vent in the ceiling, it isn’t as noisy as standard ceiling exhaust fans. Combining lights, heat and an exhaust fan into one unit is also a good solution for most bathrooms.

Keeping it Quiet

The higher the rate of airflow a fan has, the noisier it gets. Choosing a fan becomes a balancing act between the need to vent stale air and how tolerant you are of noise when you’re showering or cooking. The noise levels are sometimes described as sones, which is a measure of loudness. The more sones, the louder the fan. One sone is quiet and four sones are noisy. The other, more familiar measure of loudness is decibels, which you will see called dBA.  As a guide, breathing is rated at 10 dBA and a normal speaking voice at 65 dBA. A fan rated at 35 dBA is therefore considered quiet.

Exhaust Fan Energy Efficiency

Fans don’t draw all that much power, but it’s worth comparing brands when selecting one to find out which is the cheapest to run. This is a simple matter of comparing how many watts the device uses, as people do with light bulbs.

Best Exhaust Fan Position

The best fan position is as close as possible to the source of the fumes you want to remove, such as directly above a shower. But often it is more convenient in a bathroom to locate a combination light, heat lamp and exhaust fan in the middle of the ceiling. That’s because that’s where the wiring is. The thing to avoid is having the fan too close to a window. If the fan is close to an open window it will draw air directly from the outside and leave the rest of the room unventilated.

Ideally, your fan should have the right extraction value, quietness and energy efficiency. If you then select the right type and put it in the best spot, you have the best exhaust fan for your circumstances.

People also ask…

Do exhaust fans need to be ducted?

The need for ducting depends on your style of roofing and on what storey the room being ventilated is. Tiled roofs allow for natural ventilation and you don’t need ducting if that’s what you have. The exception to this is if sarking is being used for insulation – that’s the membrane often backed with alfoil that goes under the tiles like a second skin. If you have an upper storey, ducts are needed on the lower floor to take the steam outside through a wall vent. Houses with metal or flat roofs also need ducting because moisture can build up in smaller and better-sealed roof spaces.

Will an exhaust fan cool a room?

Because they remove hot air and steam which is replaced by cooler air, they can be said to cool a room. They are not, however, a cooling device like a standard fan. They remove steam and fumes. This certainly helps your air conditioning, but not in a hugely significant way.

What’s the difference between an exhaust fan and a ventilation fan?

You can call an exhaust fan a ventilation fan since it ventilates air. But the usual distinction between an exhaust fan and a ventilation fan is that an exhaust fan pulls air out of a room whereas a ventilation fan sucks air in.


Published: 25 Feb, 2021

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