# Switch or occupancy sensor based exhaust fan control



## JRaef (Mar 23, 2009)

katwalatapan said:


> Hello,
> 
> My application involves installing a light and exhaust fan in the washroom and switching the light and exhaust fan either via a manual switch or occupancy sensor. However switching sequence I am looking for is that the light could be turned on via a manual switch or an occupancy sensor, then I'd like at least 10 min delay to turn on the exhaust fan. The light switch could be turned off either via manual switch or occupancy sensor and the exhaust fan stays on for 20 minutes after the light is turned off and then turns off. I have reviewed products by leviton and lutron with timers and occupancy sensors, but could not find a product that could provide a delayed on and delayed off feature in the same product. Generally I find delayed off type products.
> 
> ...


I doubt you will find this as a finished "product" ready to go with that logic. You are looking at something that needs custom programming. A mfr like Leviton and Lutron would make a product like that if they could sell a million of them, but otherwise, it's too specialized. 

It would be easy enough to create with a micro PLC or "Smart Relay", but someone would need to program it. How much is this worth to you though? Micro PLC / Smart Relay = $100, time to write the program, if you are ALREADY familiar with PLC programming, 1-2 days. If you don't know what a PLC is, figure a 1 week learning curve if you are reasonably intelligent and can figure things out. Barring that, you could build it with separate relays and timers in a control panel. More hardware cost and installation cost, less programming, but still involves being savvy with control logic. Depending on how you value your time, it seems like a lot of $$ to throw at a bathroom exhaust fan. 

Why not just have the exhaust fan and light come on together and run on after they leave for a few minutes to clear the smell? The cost to turn the light off separately and leave the fan on will likely far outweigh the possible energy savings from turning it off for a few more minutes per day. I have a similar situation in one bathroom where I wanted the fan controlled separately only because of the noise, so I just put in a pull chain switch in the fan grill. Does the job.


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## micromind (Aug 11, 2007)

JReafs solutions would work and be automatic. A simple wind-up timer would also work, but you'd need to turn the dial each time you want the fan to run.

I have wind-up timers for the fans in all my bathrooms, it doesn't take much effort to use them. Instead of flipping the switch, just wind up the dial. 

Which one to go with depends on how much $$$ you're willing to spend and how automated you want it to be.


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