Bathroom Fans: Fan Size, Extract Rate and Decibel Level

Bathroom Fans come in many shapes and sizes, from round to square, and in 4″, 5″, 6″, 9″ and even 12″ versions. They are generally white or chrome, although other colours are available. Many people just pop down to a local store and pick up the first fan they see, but there are a few things you should consider about bathroom fans before you buy.

What size fan do you need? For most bathrooms, a 4″ (100mm) fan is sufficient, and is indeed the standard. If you are looking to replace an existing bathroom fan, and don’t know what size it is, don’t measure the front! The measurement is taken from the back of the fan, and it is the diameter of the spigot, or pipe, which protrudes from the back of the fan that needs to be measured. If you can’t remove the fan, (you should get a qualified electrician to do it) it is probably a 4″ one. A 6″ extractor fan is not normally required for a bathroom. They are generally more powerful and only required for kitchens.

In my opinion, the 2 most important things you should be looking at are the extract rate of the fan, and the decibel level of the fan. Obviously the best scenario is a very powerful fan with a very low decibel level. These seem to be the 2 factors in a fan which are overlooked the most! A lot of people seem to go just on looks, and think that all fans are basically the same….big mistake! 4″ fans range from an extract rate of 54m3 per hour (the minimum level required by building regulations) up to 118m3 per hour. For a standard bathroom I’d recommend anything from around 75m3 per hour, and if you take lots of baths or showers, creating lots of condensation, then anything above 90m3 per hour should so the job.

But as I say, look out for the decibel level of the fan, as a noisy fan can be particularly annoying, especially when you are having a nice relaxing bath! As a guide, anything below 25dB is considered very quiet. 35 dB would be classified as mid-range, and 45dB or above noisy.

Another thing that could be taken into consideration is the amount of energy that a bathroom fan uses. These days, you can get what are often classified as “low-watt” bathroom fans, with energy usage levers of 5-10 watts. However, even an old fashioned bathroom fan usually uses no more than 30w, and when you consider how short a time they are usually on for, the cost difference in running these fans is only pence per month. I wouldn’t focus on this is a major point to consider in your purchase.