I am wondering what the heat rating is on standard CAT5 cabling or where I can check the heat rating of my cabling by using the information inscribed on the cabling?

In my specific situation, I am trying to decide if the length of CAT5 I have sitting around can be run along and be fixed to the feed line of a old cast-iron radiator (hot water from the boiler would be traveling in that pipe, since the radiator is still in use). I am running this CAT5 because I want a dedicated 100Mbps connection via cable versus the Wi-Fi signal I am using now. If any sort of impedance would result from having the cable subjected to heat from the pipes, that would be an important thing to know as well.

Hopefully some wise sysadmins or hardware folk know the details of this sort of situation and can advise me on the best way to proceed.

8 Answers 8


The spec says -55C to +60C so you may be exceeding that rating.


Personally I think it will be ok if you lag the cable and possibly by a good quality Cat5e or Cat6 cable.

  • 1
    Definitely put in some kind of heat shield. I have cough personally seen scorched cable from dryer vent ducting, though I don't know the temperature on that. I expect cast-iron pipe carrying boiling water to be hotter.
    – Scott Pack
    May 27, 2009 at 12:25
  • 2
    Insulation is cheap - just get some low-diameter pipe insulation and wrap the cable in that.
    – MikeyB
    May 31, 2009 at 3:12
  • Never done this before, but I agree with Supermathie. Get a Cat7 and insulate it with something heat-resistant.
    – pauska
    Jun 25, 2009 at 9:38

Personally I wouldn't run a cable like that without some kind of insulation/heat shield, and I would only do that after looking for alternate ways of routing the cable.

Problems I see are:

Electricity doesn't work well with heat (heat negatively affects conductivity) - Dave Cheney already pointed out the specs regarding acceptable temperates for Cat5e.

The cables plastic jacket is likely to melt over time (or rather it will soften up just enough that it begins to fray apart under it's own weight), exposing the wires inside. This will likely result in packet loss over the cable.

And most importantly, you could start a fire. Either from the plastic jacket heating up enough that it catches fire (burning wires are great - it spreads through walls, and releases toxic gases) or after the cable frays, the exposed wire could touch the metal and short, resulting in an electrical fire (the fact that there is water involved isn't great either).

Don't take all this as overly dismissive - I've personally taped RJ12 to the outside of building ducts as a quick way to route in an extra phone - however an old style cast iron system does not sound good. A simple test would be, with the heating jacked up, can you hold onto the pipe for long without getting a burn?

  • 1
    I'm curious if there are any documented cases of a short in low voltage CAT5 causing a fire? Seems highly unlikely and alarmist to me, but I suppose anything is possible. If there are documented cases of that I'd be interested in reading about them. May 27, 2009 at 13:27
  • 1
    There is insufficient voltage to cause a fire. Worst case scenario is that a radiator running at 145-165F will cause the jacket to get brittle. May 31, 2009 at 2:56
  • Even a steam radiator at 212 would be insufficiently-hot to cause ignition of plastic. It might soften or liquify the materials, but not ignite them. If they're too close to an electrical gang box they could drip into it.. but as an insulator it shouldn't cause a short. Still a bad idea, though.
    – apraetor
    Oct 12, 2017 at 17:06

According to the table for fire forensics* (reference below), plastics melt in the temperature range of a low-pressure steam heating pipe. From the online / book research I've done pipes and radiators max out at around 120°C, and are typically closer to boiling point (100°C). **

Forced hot water operate at lower range, typically 60°C-82°C (140°F-180°F) depending on the load on the system. If your needs do not exceed operating at 140°F (60°C) regular network cable might be fine. There is also industrial high temperature cat5 cable that operate at 75°C even 80°C. I consulted globalspec.com and cable data sheets. From what I've found there is not an easy universal way to find the operational temperature from looking at the cable. You might be able to use the UL listing number or standards codes if these are printed on your cable, or information on the packaging or receipt to find the data sheet for the cable you have.

You could insulate your cable, but insulating the heating pipe will offer more protection and also save energy.

According the same fire forensics table the lowest ignition temperature for plastics is 349°C, far above any of these operational temperatures for water or steam heating systems so there is no fire hazard whatsoever from running the network cable near heating pipes. Fabrics have a much lower ignition temperature, and even these temperatures are far above the operational temperatures for steam and forced hot water home heating systems.

Electric baseboards are another matter. Do not network too close to them. Also, don't network next to your dryer duct or for that matter your boiler flu pipe. Dryer exhaust pipes, especially from a gas heated dryer, can be very hot - much hotter than pipes for forced water or steam heat. Blocked dryer vents are one of the most common causes of house fires, so clean yours out regularly.

While I believe this all to be factual and sensible, I am a software developer, not a fire marshal or building inspector. This should not be taken as professional advise and comes with no guaranty what so ever. Proceed at your own risk.

*Table data source: http://www.tcforensic.com.au/docs/article10.html#2.1 Operational temperatures for heating systems were taken from a variety of sites about heating system maintenance and fire safety. Please verify the numbers for your system by taking some measurements.

** High-pressure steam systems in industrial, and commercial settings operate at considerably higher temperatures than home heating systems.

  • 1
    +1 for You could insulate your cable, but insulating the heating pipe will offer more protection and also save energy.
    – YLearn
    Oct 13, 2017 at 19:17

When you have heat problems there are always three components:

A. radiation

Hot things radiate and thus transfer heat to other things. You put some shielding that is not transparent for heat. Any metal foil will do and a lot of other things. The shield must not be in contact with the heated element and cable because of

B. conduction

If you heat a thing up, it will conduct heat to the other side and to all other things in contact. Insulators conduct extremely badly, conductors very well. Put an insulator between which may work also as a shield.

C. convection

Even if you have insulator and shield in place, eventually there will be enough heat slowly coming through to heat your cable. You need to have some, at least minimal, exchange of the air around cable or some other means of getting the heat away continuously.

Convection (moving of the heated medium) will help: install the wire in a larger diameter tube (an inch? depends on length and bends) and make sure there is at least a small draft able to get through. If you have an altitude difference, you can get it to work by itself, otherwise put a ventilator.

A bonus is that you can also monitor the temperature on the exit.

To sum up: as already said I'd try to find another route. If not possible, then put an insulated shield (mineral wool/foam + aluminium foil is available) between and put cable in a large diameter tube to allow for draft to cool the cable.


It's a bad idea. Keep computer stuff away from HVAC whenever possible.

Depending on the type of heating system you're using, the temperature of the water in that pipe will either slightly exceed the rated operating temperature of the cable or exceed it by a significant amount (steam radiators).

The people talking about fires are probably being alarmist IMO. The problems you're going to have are brittle or separated jackets, oddball performance problems, plumbers cutting your network off, etc. Plenum or shielded cable won't make a difference here and won't address any potential building code issues.

Typically, I would recommend having drilling a hole in the floor. If you're in a historical building, there are more exotic options that will cost more money and are dependent on your situation. In one extreme example, transitioning the wiring in a early 1800's courthouse from terminal coax to Ethernet for 250 people cost about $90k. (much of that cost was restoring the damage the mainframe people made in the 70's)


I'm with David on this one: if you're asking about what kind of heat a plastic cable can handle, it sounds like fire is a possibility. Running the cable or not depends on your own judgment, but: If there's a risk of high heat it might be worth looking into plenum-grade cabling. Slightly higher heat tolerance, lower horrible-gas release, etc.:

What Is Plenum Cable, and When Should I Use It?


telephone wiring is usually at least 6" to 12" away from a radiator. I had 3 jacks (Verizon) mounted on a window frame, 6" from the radiator. no melting ever occurred!! Yes you can wire close to a radiator,Not touching the radiator or pipe!! When we install Ethernet for telephone or internet in utility closets telephone and Ethernet cables are always 1 to 3 feet away from plumbing and heating pipes. our min 1 foot from a radiator. At those distances we never have any heat/cable problems. We have neve used any high heat resistant cable.

  • The safest and easiest way is to do like everyone(cable, telephone, ethernet, computer guys do: run it up the wall and drill a hole. OR get a wire snake cut holes in the wall and pull it thru the inside of the wall.
    – user444318
    Nov 16, 2017 at 10:06

Normal Cat5/Cat6 will fail from thermal degradation of the insulation, but products do exist which can handle extreme heat, up to and including 100C (212F) temperatures resulting from runs adjacent to saturated steam lines (i.e. domestic steam heat). In fact, Chem-Guard is rated for 200C (that's almost 400F!)

There are plenty of industrial and automotive uses for this kind of cabling, so it's a solved problem. The trick will be buying small quantities, assuming you don't need 1,000 feet of the stuff.

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