I have an exhaust fan in my bathroom (used for removing the steam generated by a hot bath).

Currently, it can be turned on and off by a regular switch.

My goal: Exhaust fan should automatically turn-off 5 minutes after it is turned on.

  • 1
    \$\begingroup\$ Uhm, most domestic exhaust fans already have this feature built-in? \$\endgroup\$
    – Jeroen3
    Aug 25, 2020 at 6:12
  • \$\begingroup\$ The fan is AC, yes? If you have DC available, you can use either a DC relay or else an AC relay with a MOC30x3 IC. If you only have AC available at the site, then it may be more convenient to get a simple HLK-PM01 or similar so that you have DC and then develop the timer from there. \$\endgroup\$
    – jonk
    Aug 25, 2020 at 6:16
  • \$\begingroup\$ The other, perhaps preferred, way is to add a humidity sensor, either replacing the wall switch or added at the fan. This way, it turns on and off automatically. \$\endgroup\$
    – DoxyLover
    Aug 25, 2020 at 6:39
  • 5
    \$\begingroup\$ Switches that do exactly what you want are inexpensive and available in hardware stores. \$\endgroup\$
    – user128351
    Aug 25, 2020 at 11:36
  • 2
    \$\begingroup\$ Use a Timer Switch. \$\endgroup\$
    – brhans
    Aug 25, 2020 at 11:37

3 Answers 3


Replace the existing switch with a UL-rated timer switch. Anything else will run the risk of invalidating your fire insurance.

timer switch


Such a timer can be purchased. The switch starts the fan (AC) and runs for a few minutes after switching off. The fan is switched by a small triac and the timing is done by a CMOS gate. Its supply voltage (12V) is from mains voltage through a capacitor and a Zener. vent1



(Made in Italy)


The requirement will be readily met by an off-the-shelf 'Toilet Exhaust Fan Timer'.

Nonetheless, the following schematic, using a 555 monostable, a transistor and an electromagnetic relay, is presented for academics' sake.

enter image description here

The circuit is an adaptation of this power off delay circuit published in Seekic.com.


It's an example of a true off-delay timer.

After the switch is turned on the output would be energized. Subsequent turning-off of the switch would signal the commencement of the delay time, at the end of which the output would be de-energized.

The values of 'R' and 'C' would decide the off-delay time.

  • 1
    \$\begingroup\$ It is a good idea to expand on comments like provide a circuit diagram, care to elaborate? \$\endgroup\$
    – Voltage Spike
    Aug 25, 2020 at 7:32
  • 2
    \$\begingroup\$ 555 timer and 5 minutes is not normally a viable combination. \$\endgroup\$
    – user16324
    Aug 25, 2020 at 12:51
  • 3
    \$\begingroup\$ Homemade circuit and permanent building wiring is not normally a viable combination (building code violation). \$\endgroup\$
    – Dave Tweed
    Aug 25, 2020 at 15:47
  • 1
    \$\begingroup\$ The answer has been edited thanks to all the comments. \$\endgroup\$
    – vu2nan
    Aug 25, 2020 at 17:37

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