Can R-30 insulation catch fire if placed over flex ducts? I do not have air conditioning – only heat. Thanks, Victor
Best Answer
The air in a properly sized heating supply system should only reach somewhere between 100 and 150 deg if all is well. That temp is too low to catch anything on fire. Not only that, most flex ducting comes with insulation already integrated in it.
You will not create a problem of moisture in or on the ductwork. The duct work is insulated to keep the condensate from forming on the outside of the pipes and dripping off from the temperature differences in the attic in the summertime with AC running. So more would help. What would be bad is if the duct work is flex duct and gets mashed under the weight of the added insulation on top of it. Don't underestimate what will happen once you cover it up and can't see have may have happened to it.
About the existing decking, I feel storage is valuable in any part of the home. To cover it up and lose what may be valuable space, at least in my mind seems a shame. But if you are not using it, and don't plan on it, then there really needs to be no concern.. If that is the case then insulation added anywhere in a continuous layer is a benefit. I would if it were me, pull it up and set 2X10 material on its edge and screw it to the joists so the new insulation could run tightly between the 2X material, then add plywood over that, ripping it 2 ft. wide if need be to get it through the access.
There are products specially made for wrapping the metal HVAC ducts. Its not recommended to use wall insulation (your 40-ft roll) with HVAC because it isn't designed to handle the temp changes.
Before you insulate the ducts they should be properly sealed with mastic or foil tape. This basically means cleaning the dirt/dust off of the duct before sealing.
Best Answer
The air in a properly sized heating supply system should only reach somewhere between 100 and 150 deg if all is well. That temp is too low to catch anything on fire. Not only that, most flex ducting comes with insulation already integrated in it.