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230vac extract fan speed control - help Answered

I'm just in the process of refurbishing the bathroom of a flat I bought. It's all been plastered out already and I realised I've no extract! So, I created a plenum at hi level and mounted a fan under floor and have ducted it out.

I want to run the small AC extract fan 24/7 at low speed (kinda tick over speed) and then switch it to hi speed when either the humidity goes up (cos the shower is running) or the light goes on (assumes someone's using the WC!). I can't get to the lighting wiring so I'll need to sense that remotely. I can fit a humidity sensor in the duct work.

I've tried everywhere to find something suitable with zero joy. Is anyone here able to point me in the right direction?


Is this down as a speed controllable fan ?


Not specifically Steve but, as with any ac motor, it can be speed controlled in steps so long as cooling isn't compromised.

The step speed controlled ones usually have multiple stator windings, so they have a different pole number.

When cheap motors are run with a "dimmer" as the speed control, there is usually a provision for them to be started on full volts, and then reduced to the operating speed.

You could do this if you used one of the 12V shower fans perhaps ? I wonder if you'd get the airflow though. Is your smallest room a small room ?

Failing that, the best and safest way would be to buy a very cheap AC motor frequency controlled drive off Ebay.