Warming Cable Inside Spray Foam
Michael_Kalman
| Posted in General Questions on
Is it safe to put wire warming cable inside of spray foam insulation?
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Replies
Michael,
Warming cable can have higher than expected surface temperatures and the jacketing used on them may behave very differently when insulated. If the insulation allowed the heat to build up past the plastic jacket's melting point it would create a hazard. Probably one not covered.
The foams I have used so far are the generic urethanes and water based ones. Sunlight is not their friend but I have never attempted to enclose heated elements. The fire stop rated foams might be able to take the heat, but you would still face the potential danger to the cable jacket melting.
You might look for lower wattage per foot heating tapes like those recommended for the Sanden water line and see what kind of insulation wrap is permitted. You might also expand on the reason for wanting to foam in place a heating wire. There may be other issues and/or answers.
If you use one of the self regulating heat cables (note that these are NOT the kind with a thermostat on the end), you should be ok. Raytheon is a big manufacturer of these. They run around $2 per foot or so. These are much higher quality than the hardware store kind, and they control their temperature along the entire length of the cable with no need for a thermostat. I don’t waste my money on the thermostat controlled cables anymore.
Bill
The reason I ask is I am building a tiny home, and the P-trap had to sink below the subfloor a bit to fit (2x6 cavity with plumbing in the floor), because the p-trap went below the 3/8" ply on the bottom of the subfloor, it is exposed so I planned on having the spray foam tech install 4-5" spray foam all around the exposed area below the subfloor to protect it from freezing, but this will result in the foam touching the metal flash pan and I worry that the foam won't be big enough of a thermal break to protect the p-trap from freezing. We have -40 celsius nights where we're going.
I would try to set the drain pipe and insulation so that there is no insulation on top of the pipe. A heating cable may still be necessary at -40 .
Why would you try to avoid having insulation on top of the pipe?
Because then the pipe would be kept at close to room temperature. Put your insulation between the pipe and the exterior.
Insulation slows the rate of heat transfer. If you have insulation between the pipe and the heated interior space, that insulation will act to reduce the temperature of the pipe. If you have, for example, 70 degree air inside and 0 degree air outside, and you have R5 insulation between the pipe and inside and between the pipe and outside, the pipe will be around 35 degrees. If you put all of the insulation between the pipe and the outside, the pipe stays at the 70 degree indoor temperature, which is what DCcontrarian is getting at.
Can you bump out around that pipe a bit to keep all of the pipe on the inside of your insulation? Next best is to use slightly thinner insulation in the immediate area of that pipe. You really don’t want any of that pipe outside of the heated interior space.
Bill