Connect with us

Help, Thermal Switch for Shower Exhaust Fan?

Discussion in 'General Electronics Discussion' started by Tyler Durdem, Nov 24, 2014.

Scroll to continue with content
  1. Tyler Durdem

    Tyler Durdem

    Nov 16, 2014
    Hey Guys,
    I am doing a bath remodel and I am trying to hook the fan up to a switch that will turn it on when hot water flows through the showerhead pipe.

    Attached is a diagram of what I have.

    I plan to just wrap the thermal switch to the pipe. What I am unsure about is which way is best to hook up the switch to control the fan in a safe manner. I assume low to high voltage relay will be used. I don't want 100V running through the thermal switch at the pipe.

    I also want the fan to switch on and off from the wall, but not off if the thermal switch is in activated mode.

    It's all basically a fail safe if someone forgets to turn the fan on for a hot shower.

    Any advice and parts are appreciated.

    Attached Files:

  2. BobK


    Jan 5, 2010
    That thermal switch is designed to switch line voltage (in the U.S.), but I can understand your hesitance to put line voltage on it. You can use a transformer or wall wart to lower the voltage then use a relay to turn the fan on. You want the automatic switch and the manual switch in parallel, that way, if either one is on the fan will be on. What temp is the switch set at? Expect some delay after you turn on the hot water before the switch turns on.

  3. Gryd3


    Jun 25, 2014
    Perhaps a humidity sensor would be a little more beneficial than a temperature probe?
    My last home had a humidity sensor for the bathroom and would run automatically when the humidity in the bathroom was too high. (Usually from hot showers... it only ran inadvertently once due to me having it set too low. It was customer adjustable like a thermostat)
    It would also run until the humidity went down again. Your solution would simply run until the pipe cooled down regardless of the moisture level in the bathroom.
  4. Tyler Durdem

    Tyler Durdem

    Nov 16, 2014
    I thought about a humidity sensor but heard they can be temperamental. I figure with the switch on the pipe the fan will come on when hot water is flowing in the shower and would shut off a little while after when the pipe and water in it cools. Not much to adjust there. It's redundancy for people who forget to turn fan on.

    The switch is 35 deg c, I tested it on the kitchen faucet and it switched right on pretty quickly after water got to temp.
  5. Gryd3


    Jun 25, 2014
    They can be temperamental, especially in high humidity regions which is why they are adjustable.

    As bob mentioned above, the use of a transformer will help make things safer.
    It would be in everyone's best interest though to have something drawn up, as improper use of grounding for example in this case could allow for current flow or a short on the pipe.

    Additionally, you can rely on the thermal mass of different metals to control the delay the fan takes to turn on and off. Iron/Steel will take a little longer to heat up, and will remain warmer longer. Aluminum will take even longer.
  6. davenn

    davenn Moderator

    Sep 5, 2009
    Hi Tyler

    You need to keep this setup low voltage. Otherwise you really need an electrician to wire this up for you

    you rarely get second chances if you make a mistake. You wouldn't want to electrocute yourself or a family member

    Gryd3 likes this.
  7. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    You need a rib relay (relay in a box)
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day