You’ll wonder why everyone doesn’t do this themselves.
Need professional help with your project?
Get quotes from top-rated pros.
What you'll need:
TOOLS
Paintbrush
Putty knife
Measuring tape
Utility knife
Safety goggles
Duct caps
SUPPLIES
Aluminum duct tape
Duct mastic sealant
Fiberglass mesh tape
Fiberglass insulation rolls or pre-formed duct insulation
Protective masks
Do your allergies seem worse than usual while your energy bill is skyrocketing? It's not just the annoyances of cold weather; you've got leaky air ducts. Ducts crack with age, and if they aren’t sealed, then dust, pollutants, and other nasties seep in while making your home less energy-efficient. Thankfully, there are some simple steps you can take to seal lucky ductwork and get your air quality back to normal.
Prepping to Seal Ductwork
While sealing leaky ducts from the outside isn't as labor-intensive as installing ductwork insulation from scratch, you still need to cut fiberglass insulation to get the job done. Exposure to fiberglass and inhalation of particles can damage your skin, eyes, and lungs. Make sure to wear a mask when cutting and handling insulation. Safety goggles will also prevent fiberglass particles from getting into your eyes. Pre-formed duct insulation is an alternative that is not meant to be cut, but it can be a costlier alternative that’s also less effective if you don’t have many cracks to seal.
You also need to assess how much insulation and other supplies that you need. Take a look at your ducts and note how many cracks there are. Use a measuring tape to find the circumference of the duct. This gives you a good idea of how many insulation rolls you should buy. You will also need larger quantities of duct tape and sealant if there are several leaks to patch.
Patch Leaks With Aluminum Duct Tape
Photo: 1905HKN / E+ / Getty Images
You need aluminum foil tape designed for HVAC duct sealing. It's readily available at most hardware stores for a few dollars more than standard duct tape. Standard duct tape is fine for crafts, but those colorful rolls won't properly seal your ducts.
You'll know it's the right tape if you see "UL" on the packaging. This means it was approved for residential ductwork by Underwriters Laboratories, a certification agency that upholds safety standards in building materials.
With the correct duct tape in hand, it’s time for the satisfaction of tearing off extra long strips that fully cover the seams vertically running along the duct. Make sure the strips you tear are nice and continuous as if you're cutting a length of ribbon, not small pieces like tearing clear office tape. This ensures that it holds up for longer. Firmly press down with the tape as you roll it out, and use your utility knife to cut the roll loose.
Apply Duct Mastic
With the duct tape in place, apply duct mastic to the joints where the elbows connect to the duct. You can do this with a basic paint brush for house painting, but some people find it easier to smear it on with a putty knife.
Water-based duct mastic is the best option because it's easier to clean and will last a long time. Depending on how severe the cracks in the ducts are, you might need to include fiberglass mesh tape to reinforce the mastic. Mastic alone should be fine for small cracks, but the fiberglass mesh tape can patch gaping holes.
If you're using fiberglass insulation rolls, use the duct circumference measurement you got earlier to cut a piece of insulation from the roll. Add a couple more inches for leeway so that you can easily bring the edges together. Wrap the piece of insulation around the duct and pinch the ends together along the seam until it closes. Cut some small pieces of aluminum duct tape to make sure the insulation piece stays on the duct, then cover it with a much longer strip, pressing down on the seam.
If you're using pre-formed duct insulation, you don't need to cut it. Gently pull at the duct's elbow to expose the end and disconnect it. Put the duct cap onto the open end to keep it steady, then put the insulation over the duct like you're putting a pillow into a pillowcase. Make sure that the pre-formed insulation piece makes it over the entire duct.
Repeat
Repeat Steps 1 through 3 until all of the leaks in the ducts have been patched and replaced with new insulation. The mastic will dry in 12 to 24 hours.
DIY vs. Hiring a Pro
Sealing your ducts from the outside with the DIY approach can save a lot of money. Manual sealing is extremely labor-intensive, especially if your home is larger and has more ducts. Professional duct sealing costs around $2,250 on average, with most of that being labor.
However, your local duct installer not only knows how to thoroughly inspect your ductwork for leaks and find problem areas, but they can do more sophisticated duct sealing methods. They can seal your ductwork from the inside, which should not be attempted as a DIY job. This involves a pressure test where they remove the grilles of the supply and return vents, and plug them with spray foam. An aerosol sealant gets sprayed inside, and another pressure test is performed to see how it improves.
Aerosol sealing costs about $1,300 plus $300 for an inspection to assess the extent of the leaks. Manual sealing is needed for large leaks, and aerosol sealant can fix small leaks, so combining the two will affect the price. If the ducts are extremely hard to reach, like under the floors, the service will cost more.
The DIY route is more tenable if your ducts are easy to access, your home is on the small side, and the leaks aren’t very severe.
Frequently Asked Questions
You'll have plenty of sensory cues that tell you if your ductwork's seal is failing. You can feel weak spots when the heat or AC is running because the air is escaping the duct in that area. You might hear whistling noises or notice saggy spots on the ceiling because the duct is coming loose.
The industry standard for most home systems is 30 years, and duct systems are usually rated 15 years. Duct seals, unfortunately, don't last nearly as long and tend to only make it three to five years before they give out and ducts start leaking. Duct sealing needs to be inspected and replaced more often because normal wear and tear on ducts takes a toll on sealants.
Regular cleaning and maintenance of air ducts will extend their lifespan, but ducts should be replaced every 15 years. Sealing cracks and installing insulation will extract a few more years out of your ductwork, but they need to be completely replaced by 20 years. If your ducts are nearing the end of their life, a ductless system may be a viable alternative.
Rachel Presser is an experienced writer teaching homeowners how to navigate HOAs, home insurance, and local laws when taking on home improvement projects. She holds both a bachelors and master's in accounting and can explain the income tax impacts of homeowner transactions. Her work can be found in other publications like Home Stratosphere and LA Digs.
Rachel Presser is an experienced writer teaching homeowners how to navigate HOAs, home insurance, and local laws when taking on home improvement projects. She holds both a bachelors and master's in accounting and can explain the income tax impacts of homeowner transactions. Her work can be found in other publications like Home Stratosphere and LA Digs.
The homeowners guide to Heating and Air Conditioning
From average costs to expert advice, get all the answers you need to get your job done.
