Extractor fan solution sought

[David]

Hi there,

We have decided to fit the fan in our bathroom in the ceiling, but we are not 100% sure about what kind of extraction system is needed.

The plan is to fit a 6" in line fan in the roof and vent it like this:

we were after a fan that has a humidity sensor/ movement sensor for fully automatic operation but I cannot find an in line model like this.

Could we get a 6" centrifugal fan and vent it in the same way?

If so what are the advantages/dis-advantages of the two solution.

[Tim S]

David coughed up some electrons that declared:

Can you get a standard humidistat/PIR and use them to control the axial fan - that's what I'd do.

Cheers

Tim

[John Rumm]

An inline fan with such facilities would be kind of pointless - unless you want it to sense the humidity of your loft rather than the bathroom. ;-)

What you need is a standalone sensor like this :

also puts the humidity control within reach rather than on the ceiling or in the loft.

You can parallel a standalone PIR with the above as well if you want motion detection as well.

You could...

Advantages of inline: freedom to chose an inlet vent of your choice (TLC do a nice shower light combined vent for example), quieter operation with less vibration. Pair it with whatever controls you fancy.

CF fan: not much to recommended it except you could possibly get a "one box" solution with a built in humidistat (which would be at ceiling level)

[Phil L]

It's sealed from the loft by the ducting....

[David]

I asked my Dad and we have decided to have just a PIR sensor, my Dad says it should help to extract "fumes" when people use the toilet :-)

The bathroom is 9 meters squared, will a 5" fan be sufficient?

There is a trickle vent and a gap under the door.

AIUI the fan is activated by the PIR sensor, and then runs for a set time.

Will I need a separate timer?

Your help is appreciated.

[John Rumm]

So you would be sensing the humidity in the duct in the loft then... still not much use if you want to know the humidity in the bathroom.

[John Rumm]

IIRC The requirement for a bathroom fan is a flow of 15 litres per second. Most fans will be able to do that.

Yup - as long as it has a permanent live as well as a switched one from the PIR it should run on for a user selectable time. Note you will also need a three pole isolator switch in the feed to the fan. If this is not going to be in the same room as the fan then it should be one that can be locked off.

Not if you get a timer fan...

[Dave Liquorice]

Fan sizeing is normally derived from room volume and so many changes per hour. Fans are rated normally rated in cubic meters per hour. 15l/s is

54m^3/hr. *IIRC* bathrooms are reckoned to need 5 to 10 changes/hr so a 54m^3/hr fan is suitable for a tiny bathroom.

[John Rumm]

I just had a look through part F of the building regs, and the only mention of data for bathroom intermittent mechanical extraction is the

15 l/s figure - they don't seem to take into account the room volume.

If you apply your 54 m^3 to a room of say 3x2x2m, that does in fact give you 4.5 air changes per hour, which seems toward the upper end of what would be required in a bathroom - especially without heat recovery.

Anecdotally, I have used a 4" humidistat fan in a bathroom with a high pressure shower. I found that it would keep most of the visible steam under control during the shower, and would have the room visibly clear within 5 mins or finishing. It would then take 20 - 45 mins to dry the all the room surfaces after that (that was all tiled, with two outside non cavity walls).

[David]

So what I need is a good 5" in line fan with a timer, PIR sensor and ducting etc.

Can you recommend me a good PIR sensor and in line fan please?

I understand the good brands are Xpelair and Vent axia.