Optimising Extractor Fans

[Thomas]

Hello

So, I managed to get my en-suite extractor fan installed and wired up - many thanks for the kind responses to my earlier queries which really did help. I have a fan with both a timer and a humidity detector and after a bit of playing around "we" finally decied to put the fan on its own switch rather than on the light switch. The humidity detector means that for the most part you don't need to explicitly switch on the fan since it will start on its own soon after you start the shower and stop when the humidy level falls below the threshold. I'll leave it as an exercise to the reader to figure out when you might want to manually switch on the fan :-)

The time to clear condensation from mirrored surfaces is not as short as I was hoping - probably similar to opening the window wide. So the next thing I'd like to do is to maximise the airflow and there are two factors I'd welcome advice on:

The first is air-inflow. The en-suite door is quite a tight fit and I think the main source of in-flow will be around the eye-ball spotlights that I have fitted in the en-suite - i.e. from the loft. I'm wondering about the need to shave a few mm off the bottom of the door or add a louvre. How important is in-flow and what's the best way to provide it?

The next issue is duct length. I have a run of about 14' across the loft from the fan to the soffit exit. Whilst I can't reduce this run, the duct itself has a fully expanded length of about 24' and I was wondering if it would benefit from being cut down so that the remaining 14' is fully expanded? I understand that you should keep the run as horizontal as possible, avoid and low spots in the loft and have a fall into the exit - I think I've managed all that.

Thanks for any adivce

Thomas

[David WE Roberts]

For better airflow you should use 100mm rigid plastic pipe - like soil pipe. The wrinkly stuff has more resistance.

Sounds like you do need some incoming air - possibly at floor level - to help clear the room. Not sure of the gbest way to provide it but you have made two good suggestions.

The other option is a bigger fan (but you will probably want to try other things first).

Cheers

Dave R

[Terry Fields]

The ensuite here is SWMBO's territory; it's quite small, about 6' square, and has a tiny window and an extractor fan.

I too was concerned about levels of humidity, and by coincidence was given as a present a digital recording temperature/humidity sensor, reading to 0.1%.

Popping this in the bathroom revealed that there was a humidity spike to 99% while having a shower, falling to ambient in about 45 minutes.

As SWMBO must never be exposed to anything as rude as a draught, she showers with the widow shut. To my surprise the readings from the ensuite were the same as those of the bathroom, despite the same amount of water-vapour from a shower being dispersed in a much smaller volume.

At this point I gave up worrying about what was obviously a non-problem.

Was the weather in your area at high humidity when you tested the extractor fan? That might account for an apparently long time to clear the mirrors that isn't representative of overall performance.

I certainly wouldn't consider trimming the door, but the suggestion to go to rigid pipe for the extractor is a good one and could be done cheaply enough.

Terry Fields

[Dave Liquorice]

You can't suck air out of a sealed room...

Well I wouldn't actually shower with the window open either do damn cold in the draught! But once finished I'd leave the door open thus providing plenty of warm relatively dry air to be sucked into the room.

[Thomas]

I'm not a fluid flow expert, but I think that your solution is likely to lead to large amounts of very humid air flowing from the shower-room into the adjacent bedroom - unless you have an industrial strength fan of the type used in wind tunnels. Intuitively, I'd have thought that you'd want an inlet area of comparable or slightly larger size than the exit area. Leaving the door slightly ajar might acheive this, however I suspect that there will be significant differences in the airflow patterns at floor and ceiling levels which would still cause wet air to leak into the bedroom.

Thanks Thomas.

[Chris J Dixon]

I'm a bit concerned about your lights. I assume that they are not directly above the shower, since they would have to be room-sealed in that zone.

if they are elsewhere, they will inevitably risk allowing warm moisture-laden air into the loft. Despite your humidity activated fan, I would expect some delay before the fan starts up.

Personally I would go with taking a strip off the bottom of the door.

Chris

[fred]

If you are using accordion pleated extraction hose you might think about changing it to smooth wall pipe to increase the air flow.

[Thomas]

Thanks, the eye-balls are low-voltage and not situated above the shower.

Yes, that's what I've done.

Thanks Thomas

[Thomas]

Thanks

I had been experiencing some problems with the humidistat coming on for no apparent reason - a bit irritating at night. I discovered that the baffles/flaps which I'd position within the flexible hose were not closing correctly allowing gusts of cold air from the eves to rush down over the fan. As part of fixing that I replaced almost all the flexible pleated hose with a long length of rigid soil pipe. I believe this has both solved the baffle problem and increased the throughput significantly. All seems well (keeps fingers crossed).

Thanks Thomas