While I am new to Home Assistant, I have had some fun in the past with arduinos and am knowledgeable in basic electronics and would like to tinker a few things at my home.
When we renovated the house, we had a plan to put a toilet downstairs later down the road but did not think about the extractor fan at the time. When we finally managed to get the toilet installed, we could not route a wire to connect the extractor fan operation with the light switch. Now there is a physical switch for the extractor fan and I was hoping to automate that with HA.
So, what I have considered is to have a zigbee light bulb that would let HA know when it is turned on and have a zigbee switch that actually activates the fan.
Is my reasoning correct for this?
Hi,
As any good engineer will reply, “it depends”!
A “stupid bulb” expects to be powered 7x24, so turning the light on needs to be done via software (as it will take a while for a “stupid bulb” to boot, connect to Zigbee, and change it’s status so HASS can trigger the fan).
On the other hand, a switch module is powered 7x24 (needs a Neutral in the UK), has a switch input (pull cord?) and will signal status immediately.
Better still, get a two output module - light + fan, but then again, you’ve already said there’s no wires to connect from the light to a fan.
So, it depends on where you are in the world, how your wiring is structured (US != EU != UK), and what access you have.
A battery multisensor to detect motion/ door opening/ light level might also be worth a look.
Personally, I’d run extra wires for things as basic as toilet lights/ fans to avoid dependency on complex automations, but I’m not the one doing the remodel…
If this helps, 
this post!
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I am in Ireland, so I would assume the wiring here is quite similar if not identical to the UK standard.
I would also prefer to have the wiring done to “avoid dependency on complex automations”. In order to run the wires, I would have to make a groove on the plaster boards and re-do that afterwards - the potential for the wife to nag about a botched job is immense!
I will investigate the option with two switch modules.
I have a Zwave switch controlling the toilet extractor fan and it is included in an automation to work for 1 minute when switching off the toilet light.
You could use a Zwave, Zigbee or a wifi switch to do the same.
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The fan is likely to be easy - it will have L and N.
In UK standard wiring, the switch is just that (2-wires), and the ony location there is L and N is the ceiling rose.
I’ve successfully put Z-Wave and Matter (Sonoff Mini4RM) behind a rose by using a circular hole cutter in the centre large enough to fit the module above the ceiling (ideally with a cover for secondary insulation), replaced the rose, and wired everything in.
An easier path is to get a LED fitting with enough space for a module inside without casting shadows. Rewire using Wago 221 (smaller than 222) terminals.
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