How much ventilation is enough? Or, what size extractor fan do I need?

Whether you’re building an extension, renovating a kitchen or bathroom, or just want to check the air quality in your family home, you need to know how much ventilation is required.

Most rooms in a home won’t require extra ventilation – bedrooms, hallways, and living rooms don’t generate much moisture or smells. Kitchens, bathrooms, and utility rooms will all require some kind of extraction – some means of getting the stale or wet air outside.

A 7.5W intermittent extractor fan rated at 97m3/h.  Is this enough ventilation?The most common kind of ventilation in homes in the UK is an intermittent extractor fan. This is a fan, usually mounted in the ceiling or high on a wall, which extracts air from the room and to the outside, usually via a duct. It is called “intermittent” because it doesn’t run all the time. There are several ways of turning these fans on and off, depending on how they are used:

  • kitchen extractor fans are usually controlled manually, via a control on the cooker hood. You can turn these on and off as required.
  • Bathroom extractor fans can be controlled via a humidity sensor. The fan will switch itself on when it detects a high level of moisture in the air, and will remain running until the moisture is removed.
  • Bathroom extractor fans can also be controlled from the light switch. When you turn on the light they will begin to operate, and will turn off when the light is switched off.
  • A PIR, or motion detector, can also be used to turn fans on and off.
  • Sometimes bathroom extractor fans linked to light switches also have a “timer overrun”. They will start operating when the light comes on, and will carry on for a short period of time – up to several minutes – after the light has been switched off.

In the UK, the government has published regulations for how fast these different extractor fans need to take air from the room. This depends on the room which the fan is installed in:

Room Minimum Rate (l/s)
Kitchen – adjacent to hob 30
Kitchen – elsewhere 60
Bathroom 15
Sanitary accommodation 12

These figures only apply to Intermittent Extract Fans. There are other means of extracting air which have different regulations. For instance, Passive Stack Ventilation, Mechanical Extraction Ventilation or MEV, Mechanical Extraction Ventilation with Heat Recovery (MEVHR), and others.

It’s also important to note that these figures are for the whole system as installed – the fan, any ducting, vents and backdraught preventers. It’s not just a case of buying “the right fan” and putting it in! Getting an electrician or other professional to install the fan may be the best option – and ALWAYS demand to see the PEATA airflow test certificate before handing over any money!

Other considerations include purge ventilation and background ventilations, which we’ll look at in other articles.

2019-01-23T10:53:26+00:00December 15th, 2018|Extractor Fan, Ventilation|