I have long runs of sheet-metal duct work in my attic, which is only insulated with about 1 inch (R-3 or -4) of glass fiber insulation. The returns are not insulated at all. It seems to me that the temperature differential between the attic air and the air in the duct is much greater than the temperature differential across exterior walls, which are often insulated with R-13 or R-19 insulation. Is there a practical, inexpensive way to increase the insulation on the duct work that I can do myself?
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Wrapping you duct work with any instillation higher than R-13 is going to help. Also make sure to find all holes or cracks and fill them with sealer.
Definitely wrap duct work with insulation.Insulating traditional sheet metal ducts goes a long way toward reducing the noise of HVAC equipment and air movement, quieting pings and pops while keeping heated and cooled air from escaping along the way. There are alot specialized products for flexible or rigid duct systems that deliver optimal thermal and acoustic performance. The higher the “R” value,the more insulating power you will have. Rule of thumb for rigid sheet metal ducts is if you live in a cold weather climate, increas the R value. Same goes for flex duct.
Just wanted to add to the other suggestions on insulating your duct system. You may want to make sure you seal the duct system proir to insulating it. If you insulate it without sealing the cracks and holes it could leak air causing your insulation to sweat, capture water and maybe even start growning mold.
Yes,
You can add bats of insulation above your ductwork to encapsulate it. I would add R-30. Make sure you wrap the ductwork or at least completely cover the ductwork with the insulation. Measure the temperature at the duct farthest from the furnace and the cold air return duct with the furnace or air conditioner on. then measue it again when you are done insulating.
All good comments. First thing to do is full seal all holes and seams. There are those who advocate for not allowing ducts in unheated spaces. The next best thing is to insulate them. How… Depends upon you skill set. Wrap round or rectangular duct. I’ve wrapped rectangular with 2" iso board, taping seams. I’ve also built plywood boxes around the duct and filled it with blown cellulose. Flex duct laying on an attic floor can be covered in blown cellulose. More is better. I like to insulatte attic ducts to the same level as the exterior walls. Think of the air inside those ducts as being inside the house. - it is!
An easy way to increase the efficiency of long heat runs would be to use a closed cell spray foam. This product is not “Great Stuff”. It comes out of the can in a wide spray so you can cover larger areas quickly. You can also buy it in bulk quantity which is more cost effective. The R-value is approx. 6.2 per inch.
Depending on your attic, if gable, you might want to add an exhaust fan, cheaper and faster to extract heat. If you have plenty of room to get at your metal duct work, check for leaks, make sure outer vapor barrier is intact. Depending on attic height, you could blow in insulation to 1" of attic ceiling—need baffles at soffit…attic must be able to breathe.