I will be installing a SunTouch heated floor for 200 square feet of space. I will wire this at 240V using a double pole breaker. The specs on the website indicate the amperage draw is 10 amps for the 783 feet of heating cable. This will be a dedicated line used for only the under floor heating system. Also, the line running from the heating system the panel will be around 25 feet.

1.) Should I use a 15, 20 or 30 amp double pole breaker? The specs page indicates that the maximum circuit load is 20 amps and 15 amps with a a SunStat control (which I have.)


2.) What is the smallest wire gauge I can use? Based on some other research, it seems like 8 gauge is the way to go.

  • 1
    Picture of the "specs page" or quote the exact wording of the amperage limit there.
    – Ecnerwal
    Commented Jan 3 at 22:43
  • Please cite your "other research" for 8 gauge.
    – MadMonty
    Commented Jan 3 at 23:57

2 Answers 2


If the load of the amount of cable you will be installing is 10 Amps at 240V, then you need 12.5A @240V for code to be happy with "adequate supply for a heating load"

Nobody makes a 12.5A breaker, so you need a 15A breaker (240V double pole.) If the wording of the "specs page" is as I suspect, the MAXIMUM size breaker you can use is a 20A. There's no particularly good reason to use a 20A breaker, though.

If you use a 15A breaker, you can use 14AWG wiring. If you want to waste the 3rd wire in the 14/3 you have lying around, you can use that cable. You only need two hots and ground for a 240V heating load.

If you use a 20A breaker, you must use 12AWG or larger (diameter, smaller gage number) wiring.

There's no sensible reason to use 8 AWG (40A) wiring here, which I suspect might mean you found a 12VDC ampacity chart to mislead you, without noting that 3 volts drop on 12VDC is 25% loss, while 3 volts drop on 240VAC is barely over 1% loss.

  • Code = NEC 424.4B
    – popham
    Commented Jan 4 at 4:16

8 gauge for 10 or 20 amps would have to about 500 feet away from the panel.

For a 20 amp circuit you need 12 gauge minimum, and for a 10 amp draw that should be plenty.

You might have been looking at an automotive or boating DC 12 or 24 volt type table.

You want a 20 amp double pole breaker.

  • I have a spool of 14/3 lying around. Presumably I can't use that? lol Commented Jan 3 at 22:36
  • @geoscience123 The breaker will need to be 15 amps max for 14 gauge wire. Depending on the wiring diagram/instructions the white wire in the 14/3 will probably not be needed. Most 240v heating devices only need two wires plus ground(bare). If instructions say 20 amp, then no you can't use that wire.
    – crip659
    Commented Jan 3 at 22:41
  • That makes sense. I also have 14/2 laying around... I looked back at the specs again, and it says "maximum circuit load - 20 amps (15 amps with SunStat Control). I have the SunStat Control from the kit. So I can go 14/2 or 14/3 if I have a 15 amp double pole? Just trying to avoid buying more wire. Commented Jan 3 at 22:47
  • @geoscience123 14/2 on 15 amp breaker is okay. 14/2 should have black and white wire, so the white will need to be marked black or red at both ends. If you need neutral will need the 14/3
    – crip659
    Commented Jan 3 at 22:51

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