How to Insulate Furnace Ducts
Duct work insulation is essential in a home heating system in order to save money on energy costs. Insulation prevents the air from warming or cooling while in the duct system, especially on longer duct runs. Without this insulation, the metal duct easily transfers heat energy through the metal to the space outside the duct. It is easy to insulate furnace ducts, and the cost spent up front is quickly returned from the energy saved heating or cooling your home. Does this Spark an idea?
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Things You'll Need
- Tape measure
- Utility knife
- Calculator
- Staple gun
- Staples
- 1½-inch foil-faced duct insulation
- 3-inch aluminum foil tape
- Dust mask
Instructions
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1
Measure the duct you intend to insulate. For a square duct, measure all four sides. For a round duct, measure the diameter.
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2
Roll out your insulation on the floor. Most duct insulation rolls come in 4-by-100-foot rolls. You will be wrapping the insulation around the duct in 4-foot sections.
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3
Cut the insulation to fit the appropriate duct size. You will need to figure the perimeter or diameter of the duct (the outside edge). If you have 12-by-10-inch rectangular duct, its edges measure 12, 10, 12 and 10 inches for a perimeter of 44 inches. Add 6 inches to this measurement to allow for insulation overlap, so you will cut your insulation at 50 inches. For a round duct, multiply the diameter by pi (3.14 if calculating by hand), and then add the 6 inches. A 10-inch-diameter round duct would require 31.40 inches of insulation plus 6 inches for a total of 37.4 inches. Round up, and cut your insulation at 37½ inches.
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4
Wrap the insulation around the duct, and staple the seam together. Lay a strip of 3-inch aluminum foil tape over the seam to further secure and seal the insulation.
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5
Continue to measure and wrap your ducts with insulation until completed. For duct fittings like elbows and transitions, you might need to measure all sides of the duct (top, bottom, left and right sides) and cut a piece for each side. This will give you an insulation seam on each corner of the duct.
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Tips & Warnings
In lieu of stapling, you can just tape the seams of the insulation. There is, however, a chance this could pull apart over time.
If your duct work is exposed, it does not need to be insulated if the ducts run through the space being conditioned. Because the space will be using the heat energy in the duct, it doesn't matter if some gets released through the metal duct prematurely. Also, it is more aesthetically pleasing to leave metal ducts uninsulated when they are exposed in a room.
Wear a dust mask when working with insulation. Breathing in insulation fibers can be harmful to your health.
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Comments
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Susan Crook
Mar 03, 2010
One more thing, Energy Stars says that if we don't install flexduct correctly it will kink (like a garden hose), causing restricted airflow and overworked HVAC units. There's a new inexpensive product called SMART Flow Elbow that snaps on to form a 90 degree angle, saving energy and wear-and-tear on the HVAC units. Thought you'd like to know.
