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Thread: Garage Heater and Thermostat Setup help

  1. #1
    Join Date
    Mar 2008
    Location
    Denver, CO
    Posts
    172

    Garage Heater and Thermostat Setup help

    I've got a Dayton g73 garage heater that is currently hardwired to the 30A breaker. I would like to put in a wall mount thermostat since I can never seem to get the dial setting right and am constantly having to go over and adjust it.

    My plan is to wire a 240V -> 24V transformer in parallel on the heater circuit, run the wire to a thermostat, which will switch a relay to open/close both legs of the circuit.

    Will the extra current draw of the relay and thermostat work? The heater is setup for full wattage, which I think draws close to 30A (I haven't put a meter on it)

    Do I need a NO or NC relay? Ie, is the 24V power from the thermostat on when the room is too cold or too hot?

    Anything else I need to know?

    Thanks in advance!


    Heater.JPG

  2. #2
    Join Date
    Dec 2006
    Location
    Toronto Ontario
    Posts
    6,556
    Hi, you need a couple of fuses in the primary of the transformer, and one side of the secondary needs to be grounded.

    You need a double pole normally open contactor rated for 30 amperes, resistive load.

    Regards, Rod.

  3. #3
    Join Date
    May 2009
    Location
    Boston
    Posts
    1,213
    Bob, a fellow Creeker posted instructions which I have copied in this post in italics. I followed these same instructions and it works fine. Its a good idea to replace the built in one since it has a tendency to burn up and not work. Also you only need to run one line from the thermostat to the heater since you only need to connect 2 wires plus the ground. Ex - black from the heater to Tstat and white from Tstat to heater. Let me know if you have any questions.

    In case anyone is interested in my addition of the remote thermostat to my Dayton workshop heater, let me give you an update. Perhaps I should provide the caveat that I'm not a licensed electrician, so please consider these comments using your own good judgment based on your particular skills. I AM an electrical engineer and have been doing my own wiring for over 30 years including my own shop, and I'm pretty confident in my abilities.

    In any case, I installed the tstat a little while ago and all appears to be working well. Here's what I did.

    - First I bought a heat-only Honeywell tstat at Lowes for $20. This happens to be DPDT, but only SPST is needed for my needs.
    - After shutting off the breaker to my Dayton, I opened the bottom door and cut the wires about 2" from the built-in thermostat. My wires were red.
    - I stripped the wires that the tstat used to connect to. One goes to the Line In terminal block and one goes to the watt-selection terminal block. My plan is to wire-nut my new tstat wires to these existing wires.
    - I ran 10 awg wire through a Daytom enclosure knockout to a post in the middle of my shop. Make sure to use a cable clamp in the knockout.
    - Inside the Dayton enclosure, I connected the Tstat ground wire to the green ground screw, and used wire nuts to connect the wires I stripped from the Line In terminal block and the watt-selection terminal block. U connected the black to the Line In and the white to the watt selection wire.
    - I mounted a double junction box on the post because I wanted to have lots of room for the large awg wires. I mounted a single gang mud ring to the large box to make it a single gang with lots of wire room.
    - I did not use the 2 double pole wires, so I capped them with wire nuts. On my tstat they were red and labeled L2 and T2. I also capped the ground wire which is not used.
    - I connected my black Dayton feed wire to the tstat L1 input and the white to the Tstat T1 output.
    - I closed all the enclosures and turned the breaker back on. I set the Tstat for 52, the heater came on, and went inside for a cup of coffee.

    That's it. I remotely monitor workshop temp from my house with a wireless thermometer and it appears to be holding temp well. Let's hope it work better than the cheap tstat they built into the unit.
    Don

  4. #4
    Join Date
    Mar 2008
    Location
    Denver, CO
    Posts
    172
    Thanks for the help guys!

  5. #5
    Join Date
    Mar 2008
    Location
    Denver, CO
    Posts
    172
    On reflecting further, the heating element turns off based on the built-in thermostat, but the fan stay on for 10-20 seconds to cool the element. I think I'd like to keep that function, so my new plan is to remove the existing thermostat and rather than shorting it and switching the line power, switch the built-in thermostat wiring, so I may only need a SPST relay. I need to poke around in the heater a bit to find out exactly what gets switched in the unit right now.

    Rod, would this be where the ground goes? This seems counterintuitive.

    Heater 2.JPG

  6. #6
    Join Date
    May 2009
    Location
    Boston
    Posts
    1,213
    They way it works as I posted is you are basically replacing the built in Tstat. By cutting each side and wiring in the Tstat you still will have the heater operating correctly. The line going into the Tstat will go to the new one and the line from the new Tstat attaches to where the old one came out of the built in.

    You don't need to ground the new Tstat since the built in one was never grounded. I've had mine for 2 years now with no issues. I used 10g armored cable since thats what I had and the line from the heating element to the built in should be heaver gauge.

    Some of the older models like mine, this line burnt up since it wasn't heavy enough to handle the amps.
    Don

  7. #7
    Join Date
    Jul 2004
    Location
    Vernon, Connecticut
    Posts
    505
    Bob, I'm the one who originally posted the instructions that Don referenced. Hooking up the external line voltage Tstat as described still keeps the preheating and post running fan operating corectly. In effect, you're replacing a poor quality built-in Tstat with a better one. Plus the remote Tstat can be placed where it belongs, in the room. Mine has been working over 2 years now with no issues. Don is correct in his emails.

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