Fitting a bathroom fan...again.

[JohnW2]

Yes its a fair point. It could be designed that way. ... I guess if one wanted to know you could fiddle with the 2 pots, and it maybe possible to work it out from that.

Yes, one could try that, but it would probably have to be done 'on the bench', since both pots are within the fan casing. If, with the timer set to a long run-on period, in the presence of 'moderate' ambient humidity, one turned the humidistat pot 'right down' (so that the fan came on) and then immediately 'right up', one might expect/hope that if the timed run-on was not linked to humidistat operation, the fan would go off very soon, whereas if humidistat and timer were linked, the fan would continue running for the full timer period.

However, as I implied, the catch with this is that there could be substantial hysteresis (or just delays) in the humidistat operation - so it might take a long time for the fan to go off after the humidistat pot had been 'turned right up', even if the timer were not implicated. If the fan went off immediately the humidistat pot was turned right up, that would be pretty conclusive (that timer was not being triggered) but in the other scenario, one couldn't really be certain.

Kind Regards, John

 

[ban-all-sheds]

Whatever it does, remember that it will do it in a pretty unpredictable/non-deterministic style, as I don't suppose the humidity sensor is particularly sophisticated.

Given what a dribble of electricity they use I always think that a timer fan, triggered by the start of a steam-generating event, and set to run on for longer than is ever really necessary, is the most foolproof solution.

 

[JohnW2]

Whatever it does, remember that it will do it in a pretty unpredictable/non-deterministic style, as I don't suppose the humidity sensor is particularly sophisticated. ... Given what a dribble of electricity they use I always think that a timer fan, triggered by the start of a steam-generating event, and set to run on for longer than is ever really necessary, is the most foolproof solution.

I agree with all that.

Kind Regards, John

 

[amfisted]

All seems to be well now.

I turned the humidity setting up to max, and the timer down to minimum. I switched the fan on at the pullcord switch until it kicked in then pulled the cord again, whereupon it ran on for a few minutes and went off.

I've had a fan with timer before but never one with a humidistat, so getting the settings right was always going to present a new, if very easily solvable problem.

Thanks again for your responses.