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XPS foam near heating ducts

12K views 3 replies 3 participants last post by  Termite 
#1 ·
I am going to insulate my rim joists this summer with XPS foam (spray foam is just to expensive)... but I have an issue with heating ducts that run to the rim joists then up through the floor... Can XPS touch heating duct work? should there be clearances for this? I have about 3 joist bays that have duct running into the floor and up through the walls to the second floor (I think this is called riser duct?) If I cant put XPS there what other solutions do I have for those areas? 90% of them I can finish off with 2" XPS with out any problems... it's just those that the HVAC duct runs up to that are the problems...

thanks!
 
#2 ·
The temperature of the heated air in those ducts is 90-110 degrees F. Your body temp is 98.6 F. Does the foam melt or smell bad when you rub it on your arm? Yes you can use ridgid foam around the riser ells. You could also stuff the area with fiberglass insulation if there is not enough access around the duct at the rim joist. You will just itch for a couple of days.
 
#3 ·
Thanks! Just wanted to make sure, never know what kind of code I could be breaking if I don't ask first :)
 
#4 ·
There are no clearance requirements to ductwork. However, be very careful not to put foam in close proximity to a furnace or water heater vent, or similar fuel-burning appliance vent....They get much, much hotter.

XPS foam cannot be left exposed inside any accessible area of a home. That includes attics, mechanical rooms, basements or anywhere else. It must be covered with an ignition barrier of 1/2" sheetrock or 3/8" plywood to be code-compliant.
 
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