Intermittent Vs Continuous Bathroom Extract Fan?

[munch88]

Hey guys!

I've been looking at a Vent Axia silent extract fan for a bathroom with shower.

The fan continuously runs and boosts when the light is switched on or via humidistat.

I was looking at the spec and the extraction rate is only 15 l/s which is the bare minimum for a small bathroom!

This fan is about £130 so would expect a higher extraction rate especially from a leading brand.

Is the low extraction rate due to it continously running?

In guessing it's very good all day round but what about when shower is used?

It's going to take quite a while to clear humidity.

Does anyone have more knowledge or experience with this type of fan?

Thanks

 

[Richard Burns]

Odd arrangement there with the continuous and boost.
However silent fans tend to be only silent because they have low extraction rates and the fan is running slowly.
A continuous extract fan can run much more slowly than and intermittent fan as it is a continuous process; it is meant to ensure there is no long term build up of waste products in the room.
The boost should be well above the minimum and so should clear the room reasonably so long as you have sufficient air flow available into the room.

 

[Fox]

Although perhaps less common than intermittent fans, continuous extraction provides constant air circulation to prohibit damp forming, which is key for rooms prone to high relative humidity levels (kitchens and bathrooms for example).


If you take a look at document F of part L of the building regulations, the requirements for bathroom extraction are 8 litres per second for a continuously extracting fan or 15 litres per second for an intermittent fan.

15 litres per second may not sound like much, but think of six, 2 litre coca-cola bottles of air being extracted every second - fairly impressive and more than ample for a small bathroom.

If you're set on fitting a larger fan, look at a kitchen extraction fan which will extract 60 litres per second (again meeting requirements of document F part L). In my opinion, it's not worth the additional expense or aesthetic balls up. Also, bear in mind these require a 6" duct/core hole, rather than the standard 4".

Hope this helps

 

[munch88]

I had a look and 15 l/s complies with building regs.

15 l/s Is when it's in boost, continuous running it's 6 l/s.

My only concern was when someone has a shower. I'm guessing it will just take longer to extract.

 

[Fox]

Boost can be triggered by a pull switch or humidistat - ideal for when the shower is running