Bathroom extractors with humidistats

It would trigger the run-on timer. An alternative would be to forget the timer and use a pipestat on the hot feed. This would switch after a short delay but stay on until the pipe cooled below the set point. Given our moist climate, I think a pipestat or flow switch (on the hot feed, not what I said earlier) would be a better solution than having a humidistat. This has been a really useful thread. Thanks to everyone who has offered their opinions and experiences.

The humidistat, starts the timer, when the room humidity rises above a certain level. The timer does not begin to time-out, until the humidity is below the set level.

Personally, I would include PIR triggered, so the fan comes on, when ever someone uses the room, rather than relying on light triggered - not everyone turns the light on.

Not good enough, to be absolutely relied upon, to trigger the fan timer. Use a PIR.

They take some while to trigger due to moisture in the air, by which time the moisture in the air will have begun to settle out on the cold walls. They are better used as a means to keep the fan running, until the moisture in the air has been cleared. Use a PIR to trigger the fan/timer, when you walk in the room, then leave it to the timer + humidistat to decide when to turn the fan off.

That is outdoor humidity. Indoors is very different- I constantly record mine, and RH varies between 45 and 70.

Yes, the humidity sensors are not instant. When installing them it's often recommended that they are left at least a day to acclimatise before any adjustments are made.

There is a good reason why we use humidistats. Because the thing that concerns us is condensation.Not time after shower. Not presence of shower.

Presence of humidity close to 100% is what we are trying to eliminate.

In practice even if its pouring with rain outside, unless you are in a tropical climate it still wont be 100% RH inside the house on average. So the humidistat will always find some relatively dry air to suck into the bathroom from the rest of the house.

I have a triggered by light or triggered by humidity It works extremely well.

Only case it doesn't cater for is a strong smell of s*it or vomit, but I can close the door...

IME absolutely 100% reliable...

If steam has reached the cold walls its also reached the fan.

Condensation is only the issue in the ling term. The humidistat ensures warm dry air enters the bathroom.

FFS when I shower the whole wall over the bath gets sopping wet. NO PIR triggered fan is going to stop that.

The humidistat ensures that no walls or windows STAY wet.

I have a few temperature/humidity sensors scatted around my house Temp/RH Outside (in sheltered position) 10C/68% Loft (tiles are currently wet*) 9.5C/83% Shed (Old outside toilet now housing boiler) 16.5C/49% Downstairs Living Room 21C/45% Upstairs bedroom 21C/43%

Claimed accuracy of sensors Temp +/- 0.5C RH +/- 3%

Exactly. Once you add heat to a house the RH drops accordingly.

In fact indoors RH is *higher* in summer as less heat is added to the house.

People with antique furniture know it bows and warps in winter, with CH, not the summer.

Amply demonstrates the point.

Our design when we refurbished: Extractor fan (not linked to light). Separate humidistat, which triggered Run on timer which also had pull switch.

This covered our requirements: (1) Turn on light without triggering the fan (2) Turn on fan directly with run on timer (3) Turn on fan when humidity is high, with run on timer

So you can go for a wee at night without waking the house up.

You can trigger the fan if you decide you are polluting the atmosphere.

Any time the bathroom gets too humid the fan turns on.

This has worked for us so far.

It is an expensive set up as we have the fan in the roof void and two separate controllers which are linked. However it has worked very well.

Cheers

Dave R

If the bathroom is heated then will there be any really cold surfaces? The nearest in our bathroom is the mirror, double glazed window, and glass shower screen.

Turning on the extractor fan is always a good move before a shower. In our bathroom we use the pull switch to on/off and trigger the run on timer.

Some time later the fan switches off, then a little later switches on again from the humidistat triggering the run on timer.

Cheers

Dave R

The problem is that as the humidity rises, at some point the surfaces will fall below the dew point and water vapour will then condense on them.

At 20degC and 75%RH the dew point is about 18degC, so any surface at or below that temperature will attract condensation.

No cold water pipes or cistern ?

not as cold as the windows

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