Effect of spray foam on AC refrigerant lines & electrical wiring
Finally we are ready to make our attic a conditioned space. R38 on 2x6s and R21 gable walls. The new closed-cell Demilec HFO looks very promising. After all the research, I’m done to one major concern:
The effect of the installation heat upon my Romex, alarm system wiring and AC refrigerant line. About five feet of the latter would be buried in the foam; and quite a few runs of Romex and low voltage alarm wire would also be buried. The concern is not only the initial, temporary 200ªF temps of the foam as it cures but the lack of ability for the heat of Romex wires when they are in use to dissipate due to the effectiveness of the insulation. I can’t imagine what the initial heat would do to the rubber tubing on one of the AC lines or the copper tubing underneath.
I’m attaching some article links below. Generally Romex is rated at 90ºC (194F). Some foam manufacturers correctly say that there will be no air to start a fire if the wires overheat, but if the wires short out from melting insulation, other parts of the system could be affected and cause a fire elsewhere. Multiple Romex wires put together through bored holes in the rafters increases the risk. I have scoured the internet and have found only a few reported cases where the intense heat has left the sheathing intact but melted the wire insulation beneath. But admittedly not many cases are reported. Common sense tells me not to do it.
My solution to this may be:
1-Remove the wiring first and put it in conduit over the sheetrock when I install that over the foam.
2-Or I could spray foam three inches instead of five—thus not touching the wires– and then use cellulose for two inches.
3-Or de-rate the amperage for the breaker that covers the attic circuit and/or change the standard breaker to a combo AFCI-GFCI one.
4-Some installers report the using the trick of spraying a quick inch or so on the wires, let it cure 15 minutes and then spray the rest of the cavity. That might solve the initial overheating problem but not the long term inability of line heat to dissipate. In ordinary use –mostly for lighting–not much of the 15 amp capacity would be used, but it’s hard to predict what certain outlets might get plugged into them in a house. This is an old house with some updated wiring and fairly new main panel 200 amp service, but this one line covers two bedrooms and the hall, outlets and lights.
5-For the AC line I can reposition it so it only goes through four inches of the gable wall, or better yet since my AC is already over 30 years old, rip it all out and install a new, smaller, more efficient unit away from the foam.
I’d appreciate any feedback on this.
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