How to Insulate A/C Ducts
Without insulation, air moving through duct work will warm up or cool down depending on the application. Warm air coming from a furnace will significantly cool down, and cool air coming from an air conditioning unit will significantly warm up. This is compounded when duct work lengths are long. Metal duct work is a great heat conductor, and this is one of the reasons the heat loss can be so great. However, when you insulate A/C ducts with a simple covering of fiberglass insulation, your HVAC unit's efficiency will greatly improve. Does this Spark an idea?
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Things You'll Need
- Tape measure
- Utility knife
- Calculator
- Duct wrap
- 3 inch aluminum foil tape
- Staple gun
- Staples
Instructions
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1
Move things away from your A/C ducts if possible to make the insulation installation easier.
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Start at the HVAC unit and measure your duct work dimensions. For square duct, measure all four sides. For round duct, if you can't get at an end to measure the diameter, you'll need to figure it out. Take a tape and measure the circumference of the duct (distance all the way around). Take this measurement and divide by pi (3.14). For example, if you have a distance around your duct of 25.12 inches, and you divide that by 3.14, you'll come up with 8. This is your duct diameter.
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3
Figure out your insulation cut size. Insulation usually comes on a 4 foot wide by 100 foot long roll. So unless you need a shorter piece, you'll typically be putting up 4 foot long pieces. For square duct, add up all four dimensions (e.g. 12 by 10 duct would be 12 plus 12 plus 10 plus 10, which equals 44 inches). For round duct, take the diameter and multiply by pi (3.14). (e.g. 10 inch duct would be 10 times 3.14 which equals 31.4 inches). The insulation needs to overlap a little so you can tape the seam of the insulation. Take the above measurement and add 6 inches to have appropriate overlap. (e.g. Your 12 by 10 duct, cut size 44 inches would turn into 50 inches after adding your 6 inches. Your 10 inch duct, cut size 31.4 inches would turn into 37.4 inches). You can round these numbers up to the nearest half inch for ease of cutting.
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Cut your insulation using a utility knife. Wrap it around the A/C duct and pull it tight. Don't pull it too tight, or it will lose some of its insulating ability.
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5
Tape the seams together where the insulation overlaps with 3-inch aluminum duct tape. The insulation should be snug around the A/C duct now.
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Continue measuring and cutting your insulation until all your A/C ducts are insulated. Tape all seams to ensure an airtight fit.
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Tips & Warnings
For duct work fittings, elbows, insulating around duct take-offs, etc, cut pieces of insulation as required to fit. Full wrap-around pieces won't work in these instances.
For extra support, staple the insulation seams together before taping. This may improve the life of your insulation.
