How long for extractor fan timer?

[mxo]

I have a new bathroom extractor fan, its timer is set by default to continue to run for 35min when turned off. This feels long and it’s a small bathroom, is there a way to calculate how long an extractor fan should run based on the room size?

 

[just pumps]

Size of bathroom and bath or shower migt help the boys.

 

[mxo]

Room size is roughly 2m x 2m, 2.5m height, with shower bath

 

[Taylortwocities]

15minutes tops.
This assumes there is adequate spaces for air to enter the room, or the d as n will not extract efficiently.

 

[ericmark]

I seem to remember it is in one of the parts of the building regulations, seem to remember 15 minutes.

 

[stem]

Much will depend upon how much air the fan actually shifts when it's running.

Your room is 2m x 2m x 2.5m = 10m3.

An extractor fan rated at 90m3/hour would change the air in the room 9 times an hour. Personally I aim for 3 to 4 changes of air which in your case works out at approx. 25 minutes.

An extractor fan rated at 120m3/hour would change the air in the room 12 times an hour, which works out at approx. 20 minutes.

This assumes that the location of the fan is correct though. It needs to establish a flow of air across the room, so ideally the fan should be located diagonally opposite to source of the replacement air; usually the door. [make sure the door doesn't fit too tightly to restrict air flow] If the fan is located directly at the side of the door the majority of the room won't benefit from a direct flow of air, so it would need to run for longer.

You may also want to consider:

1. How much steam is produced: Showers produce more steam than a bath & some people shower for 2 minutes others for 10.

2. If you have towels drying on a towel warmer, that moist air will continue to be produced after the room is vacated and so you might want to leave the fan running for longer.

3. If the bathroom is heated. Warm air carries more moisture than cool air. Meaning that more moisture will be extracted in less time when the air is warmer. Also there will be more condensation to get rid of, if the fabric of the room is cooler and allows more condensation to form.

 

[mxo]

The fan operates at 67m3/hr, so based on the above calculations, that’s 6.7 times an hour, for 4 air changes: 4/6.7 * 60 = 35 min, so perhaps the current setting is actually ok?

 

[stem]

You could try a shorter time [he says wearing his energy saving hat ] and see what happens. If you aren't left with a fresh dry bathroom you could always put it back. Assuming your fan has an adjustment facility.

 

[Sureitsoff?]

some fans have an adjustable run time. there might be a small circuit board inside with an adjuster on it

 

[mxo]

It has a timer module so the time is configurable, just need to decide what to set it to

 

[ericmark]

In a room with no openable window (i.e. an internal room) an intermittent extract fan should have a 15 minute overrun. In rooms with no natural light, the fans could be controlled by the operation of the main room light switch.

I had thought the bit about working with light switch had been removed, seems I was wrong, so if natural light must be able to switch on without the lights, I remember @ban-all-sheds saying about use of double pole switches so a push switch could be included as well, but thought dropped when we went onto LED lighting.

 

[mxo]

There’s a 2 gang switch to turn the lights and fan on separately

 

[EFLImpudence]

I seem to remember it is in one of the parts of the building regulations, seem to remember 15 minutes.

You remember wrongly then.

There is nothing in the Building Regulations about fans.

 

[ebee]

as a rule of thumb. you might try 20 mins and see how it goes. it is only a rule of thumb though

 

[JohnD]

If you have a modern fan with a ball-bearing motor and rubber mounts, that is practically inaudible, I would leave it running long enough to clear a steamy bathroom on a cold frosty night.

If you have a noisy old fan that is an annoying nuisance, throw it away and buy one as above.