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Garage door open switch to Honeywell thermostat

Discussion in 'General Electronics Discussion' started by DRW, Dec 21, 2011.

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  1. DRW


    Dec 21, 2011
    I live in Minnesota and have a gas garage heater that is controlled with a simple digital Honeywell thermostat. I keep it at 40 degrees which is as low as it goes just to keep things in the garage from freezing. Twice now (in 3 years) I have left the garage door open and the heater has run all night. I'm thinking of wiring a reed switch to the garage door and to the 24v? furnace on wire of the thermostat so that the heater will not run if the garage door is not closed.

    Initially, I was thinking I needed a relay but now I'm wondering if I can run the 24v from the thermostat directly through the reed switch and then to the heater.

    I'm just looking for any advice or warnings I'm not considering on why I might not want to do this.

    Thanks in advance
  2. jackorocko


    Apr 4, 2010
    All you need to do is open circuit the thermostat control to the heater, but what exactly do you plan to use on the garage door to open circuit the thermostat control? ARe you planning on using an electrical signal or a mechanical switch to control that?

    What is a reed switch?

    edit: After looking up what a reed switch is, I assume you plan on using one in series with the 24V thermostat signal to the heater and using a physical magnet on the door and locate the reed switch appropriately? If so I don't see why this wouldn't work. Use a NO reed switch.
    Last edited: Dec 21, 2011
  3. duke37


    Jan 9, 2011
    Welcome to the forum.

    Reed switches are somewhat delicate, I would think it better to use a microswitch. The standard switch can manage 5A at 250V AC.
  4. DRW


    Dec 21, 2011

    Thanks for the reply. Yes, I was just going to mount the magnet on the door and the wall so that it would make contact when the door closed. I was just going to run the 24V on signal through this switch in series.
  5. Resqueline


    Jul 31, 2009
    Try to estimate the current going through the thermostat circuit. If it's 100mA or less you could use a reed switch, if above then a microswitch would be more durable.
  6. KMoffett


    Jan 21, 2009
    How important is it to keep the garage interior from freezing? As an alternative, you might consider (ONLY IF THERE ARE MULTIPLE FUNCTIONING OBSTRUCTION SAFETY SWITCHES) an automatic, timed door-closer. A reed or microswitch indicates door is opened and starts timer. At the end of the time, the timer trips the door-operate switch and closes the door.

    Last edited: Dec 24, 2011
  7. DRW


    Dec 21, 2011
    I'll look around for different types of switches, a mechanical micro switch may be the easiest choice. Looks like a lot of the magnetic switches are 12V, I'm assuming I would need a relay and a 12V power supply. I like the idea of it automatically closing the door but I am wanting to keep it as simple as possible and my primary concern is that the heater doesn't run all night.
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