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I'm working on adding a 7500W electric heater to my garage, and am wondering how to hook up an external double pole thermostat.

What is giving me some concern is that on the double pole thermostats I see they have an amp rating which is below the amp of my electric heater at 220V.

So my guess is that the double pole amp rating is for users who have in-line / series connected power to their electrical heating devices, but still want a graphical display?

I bought the Dyna Glow 7500W heater link

Here is the wiring diagram:

enter image description here

Because the thermostat is double pole, do I not need to worry about the current running to the thermostat?

My interpretation of the wire diagram and system intent, is that my external 220V double pole thermostat is going to be powered from L1 & L2 at 220V with 100mA or whatever low power (ie. the powered front end with the display with buttons) and then I hook up the "load" from the thermostat to 1 & 2 which then switches on the heater thermostat and the turn dial is set to max temp on the unit?

My thought is that the 1 & 2 line would be like 14 awg, and just carries some small current to the switch to activate the furnace thermostat to turn on?

Am I wrong? Will the ~31.5A be running through my double pole thermostat in someway and I need to find a heavier duty thermostat? (I understand if you have simple baseboard heater and you put a thermostat in series you have the current running through your thermostat).

I actually expected to see four wires on the external thermostat section with L1, L2, 1, and 2. When I pop open the furnance backplate will I find four wires or will I need to splice in 14 awg to L1 & L2 somehow too?

Am I totally off here? (Yep, I'd love to convert the 220V to 24V DC too and add the third Nest thermostat to the house, but first I want to make sure I understand the original intent of the wiring here!).

UPDATE: Here are the terminations and the thermostat.

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  • What make/model of thermostat are you attempting to use? Note that the wiring configuration there is a bit weird, and thus not compatible with some/many? line-voltage 'stats... Nov 1 '20 at 16:39
  • @ThreePhaseEel -- so... I forgot to hit the external thermostat switch, but I wired up the thermostat to the unit, and it exploded....! What I don't get is that the manufacturer is selling a 22A capable thermostat and claiming it works with their furnaces.
    – Leroy105
    Nov 2 '20 at 2:07
  • Any chance you could upload a wiring diagram for the final product? I'm trying to wire up a double pole thermostat to a 10,000 watt Dynaglo heater and their customer service has been no help. I'm a visual person so a diagram would be best. Thanks!
    – J Mags
    Feb 1 at 0:42
  • @J Mags (Take a look at my sample thermostat above)-- I'm swamped at work but you want to connect L1 & L2 to on the thermostat (the two inside wires) to L1 & L2 on the heater; connect the top wire (above L1 on the thermostat) to the 2 terminal on your heater. Hit the switch on the back of the heater to go to the external thermostat. So you have one unconnected wire hanging off the thermostat.
    – Leroy105
    Feb 2 at 19:40
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That thermostat won't work with your heater without extra wiring

Your problem is that the thermostat you have won't work with your heater; in fact, no electronic line voltage thermostat will work with your heater if you wire it as depicted in the heater's wiring diagram, because that arrangement only provides a single line leg to the thermostat location, leaving the thermostat with no suitable path to return its own operating power back to the source. You'll either need to bring L2 over to the thermostat box as well with only the L1 side load wire connecting to the return to the heater, which requires running a 14/3 from the heater to the thermostat, or use an electromechanical thermostat instead of an electronic one. The good news is that the thermostat won't be switching much power, at least, so the wattage rating isn't critical.

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  • So, I connected the other L1 & L2 terminals to the thermostat and the display powered up. What do you think of that to power the first pole of the thermostat? The second pole didn't last though connected to 1 & 2, but I think it's because I forgot to switch the external thermostat switch (Yes... I wish there was as better diagram and had a clue of the actual connections in this unit).
    – Leroy105
    Nov 2 '20 at 4:22
  • @Leroy105 -- yeah, you'll then need the L1-side load connection on your thermostat to connect to the load wire Nov 2 '20 at 4:24
  • What do you think on the exploding thermostat on 1 & 2, don't forget to flip the external thermostat switch next time...?
    – Leroy105
    Nov 2 '20 at 4:25
  • @Leroy105 -- you'll want to flip that switch to External yes, but I'm not sure what terminals on the thermostat you're referring to Nov 2 '20 at 4:25
  • I posted the back image of the thermostat. I connected L1 & L2 from heater to L1 & L2 on thermostat, and 240V to L1 & L2 on the heater. From 1 & 2 on the heater, I connected to the the remaining outside connectors on the thermostat. That seem right?
    – Leroy105
    Nov 2 '20 at 4:30
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On the wiring diagram the large and small boxes marked KM are parts of a relay that carry the full current for the coils, any line voltage thermostat will be able to carry the current from the control circuit.

The thermostat can be wired with #14 because the instructionss that are part of the UL listing allow it. I'm guessing there is some internal fuse/fuselink not shown on the diagram.

I am not familiar with full Nest product line, you would need a model with separate control voltage or you would need to build one.

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    To try to answer what the terminations look like I went to Dyna-glo parts page ghpgroupinc.com/product-catalog/heater-parts.html and they don't even list that model number to search for parts. Dwell on that a bit. Nov 1 '20 at 16:59
  • Went to hardware store and bought 40amp breaker and some 8 gauge to dry wire this before for running 100ft of conduit. A 220v relay sure would make sense. I'll open up unit
    – Leroy105
    Nov 1 '20 at 17:00
  • Ha....... Heater is missing the bracket for the ceiling. This thing is scary. The terminations are super lightweight. They provide 220V L1 and L2 and you use it to power up external thermostat. On phone can't post photo. I stripped the screw on the 1 terminal, not joking seems like it's loctited shut as 2 terminal no issue and the L1 and L2. There is a huge relay in the box. Returning this one, may get different brand... This thing seems sketchy with no UL mark
    – Leroy105
    Nov 1 '20 at 18:28
  • On the back of the unit, there is a switch for the interntal thermostat vs. the external thermostat. I forgot to flip that switch, turned on the unit with internal thermostat and then proceeded to explode my thermostat.... You think if I connect a new thermostat + hit that switch it'll be okay?
    – Leroy105
    Nov 2 '20 at 2:11

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