I'm running new thermostat wire to my boiler (so I can get a c-wire to new thermostats). The old wiring runs along the heat pipe before it attaches to the zone valves. It used to be secured by wire, but someone removed it (left the wire) and used electrical tape to secure it. The old wiring has a cloth like jacket, which probably can handle the heat. The new stuff has a vinyl like jacket. I'm unsure if it's ok to have it that close to the heating pipe. Is there a professional/proper way for doing this?

UPDATE: I found the manufacturer's spec sheet on the wire. The jacket is PVC and the wire is only rated to 60 degrees Celsius. To me, that means you shouldn't have it touching the heating pipes.

  • 1
    I would tend to keep electric type wire away from hot stuff, unless it was a sensor type for excess heat. If possible mount to joists or something and just have a short section down/up/sideways to valves/devices. Only type I would tape to pipes are the freeze protection(heat) cables.
    – crip659
    Jan 6 at 22:59

3 Answers 3


The electric tape is not good when exposed to elevated temp for long time.

The glue on the tape will dry up over time and the tape will not fulfill its function.

For this job using simple tie wraps (zip ties) will do the trick.

  • Please see my update on temperature spec of wire. Jan 7 at 14:38

Use plastic cable ties to loosely attach your thermostat wire to the bottom of pipes in areas where it's convenient to use the pipes for routing.

The 60C temperature rating means a couple of things:

  1. The electrical rating of the cable is tested up to 60C. For example, if it's a 150V cable the insulation may fail above 60C. If you have a 150V thermostat you have other problems. :) Assuming it's 24V, you'll be fine, electrically, at higher temperatures. There will also be a current limitation but assuming you're using a newer electronic thermostat that won't be an issue for you either. For example, 18AWG wire is good for 14A at 90C. That's if the whole wire is heated to 90C. At 60C it'll be a higher rating. You hopefully will be using much less than 1 amp. This is not an issue.
  2. Deterioration of the insulation. First of all, if the pipe is 90C and you hang the wire loosely beneath it, the wire will not become heated to 90C. It might become 60C, maybe even more. If the wire is designed to last 40 years, maybe as a result it will begin to deteriorate after 20 years. It's up to you how much you care about this. The wire will last longer than the furnace, the thermostat, and probably the next major renovation of the house and even if it begins to deteriorate... we go back to the fact it's 24V. The insulation would need to almost entirely disintegrate before the wire actually failed.

Just don't tightly bind the wire to the pipe ... keep the ties loose and don't use a lot of them.

  • Interesting. I didn't think about the heating of the wire due to current (just worried about the pipes). Loosely tying the wires to the pipes is probably what most pros do (it's fast and not too hard on the wire). Jan 11 at 16:22
  • Just don't use tape. The glue is certainly impacted by the heat. If you don't have wire ties to hand you can make twist ties with off cuts of the thermostat wire!
    – jay613
    Jan 11 at 16:37

In the end I did something different, so I thought I'd post it. While I think what jay613 said is what most pros do, I can take the extra time to make sure it all lasts. I put pipe insulation around the pipe and then secured the thermostat wire to that insulation (I used some of the old thermostat wire removed from the jacket).

Note: the rubber insulation is rated at a pretty low temperature (couldn't use it). I used the foam stuff that is rated for 200 F (my boiler is set at 170). If you have steam, or want to be more careful (worried about the foam "outgassing"), you could use the fiberglass insulation.

I verified the electrical tape did indeed "dry up". It was hard and brittle and fell off with little force. Also, I noticed the plastic tie wraps close to the boiler were discolored and broke easily. And, in places where the old thermostat wire was firmly attached to the pipe with tape, the cloth jacket had discolored and was getting hard/brittle.

My guess is the uninsulated wire loosely securing the thermostat wire may have been from the original install.

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