Humidistat question FAQ

I have used and older version of the Manrose humidistat (the one with a proper adjustment knob on the front, and no timer function) a few times, and it works well and is reliable.

Something like:

Note that using a separate humidistat can need more elaborate wiring in cases where you want the run on timer as well as the humidistat function:

Thanks John. Looks a bit more involved than I originally thought. I suspect buying a new fan with a built in stat will be a lot simpler!

Tim

Possibly... much depends on exactly how you want it to run. For humidistat only control it is easy.

If you want light switch control with run on as well as external humidistat, then it might get more complicated as I discovered. The "smart" fan I selected can do stuff like delayed start on a light switch trigger (so it only starts for longer visits) and can do things like a timed refresh a few times a day. It looked easy to wire since it had an external trigger input as well. The complication was that when you asserted the trigger, it also made its light switch trigger terminal live. So the humidistat coming on would also turn on the light :-)

One thing I would note about humidistats is that they may need seasonal adjustment to account for the general changes in ambient humidity. It is a whole lot easier to do that when it is in a remote unit that you can easily get at rather than at the fan itself.

I suspect this is the optimal strategy.

I have a small bathroom where this was indicated. The fan was pretty cheap and after 22 years it's sill working fine

I think it was aboout £40 as against £20 for a run-on fan

Looks like £60 is what they cost now

In our case we have 3 components.

(1) Fan (in the loft upstairs, between floors downstairs)

(2) Humidistat

(3) Run on timer

The run on timer is triggered by the humidistat.

There is also a pull switch on the humidistat to trigger the run on timer.

Controls by Xpelair.

We didn't want the fan to be turned on by the light (for example by someone wanting a wee in the middle of the night).

We did want to be able to turn the fan on during the day without having to turn the light on.

We wanted a humidistat to cope with any excess moisture in the bathroom at any time of the day or night.

All done 12 years ago and still working fine. Not a cheap option though.

Cheers

Dave R

I haven't installed a humidistat, but have been considering it for a shower room. I'd assumed that the output was on while RH was above the threshold, so why would run-on be required?

The way mine works is this.

It is controlled by the light, and doesn't run on *unless* the RH is above the threshold.

In fact it can be triggered by driving rain getting into the exhaust vent.

It can also be switched on permanently on a pull cord

I guess if it had a run on after the light went off, that would be another mode.

Why does any fan run on?

just because you've left the room, doesn't mean the need to change the air has occured.

The olfactory evidence of a (ahem!) "biological event" lasts longer than the event itself ;-) hence the need to keep changing the air for a while afterwards. In ignorance, I wouldn't have thought that was true if just trying to get the RH down

I don't know what the current prices are, but we've had one of these for the last 8 years or so and it works pretty well:

That's right

Depends on your use case and particular requirements... If you have also want the fan to run when the light is turned on then that may be one case. In the case of mine it will trigger once the light has been on for

You might want the ability to have a manual option and have the fan run for 5 mins to "clear the air", in response to a momentary action switch. You would need a timer for that as well typically.

Also some smart fans have periodic run modes where they can be set to run 10 mins a couple of times a day to keep the air fresh.

Yes, I understand that run-on is useful to help remove someone else's "unpleasantness" from the air (one's own is never as bad ;-) ), but my point was about RH.

Linking the fan to the light is mainly useful for an "internal" bathroom (with no windows) as you have to turn the light on to use it even in the daytime.

The Romans had a relevant proverb: Suus cuique crepitus bene olet - Every man likes the smell of his own farts.

(I don't think we've invented a fart detector yet.)