How to Seal Leaky Duct Joints

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What You'll Need
Clean rags
Candle or matchstick
Spray cleaner
Aluminum foil tape
Silicone caulk
Caulking gun

Energy efficiency is a topic that is constantly on the minds of many home owners. Not only will a more energy efficient home help ensure you are kept comfortable during the summer and winter months, but there is also a potential for huge savings in the energy department. With that in mind, one area of your home that is a possible energy hog is the duct system. A lot of air can escape out of a duct system from gaps in the ducting, holes worn over time, and leaky duct joints. Luckily, fixing leaky duct joints is easy and can be accomplished with little time and effort. By following these simple steps you can rest assured that your home remains as energy efficient as ever.

Step 1 - Locate the Leak

The first action you'll need to take is find out where your duct system may be leaking air. Fortunately, discovering the areas in your duct system that may be leaking is an easy process. Common problem areas to check are around joints and fittings where the ducts are connected. For the larger leaks, you should be able to visibly see the gaps, especially if some joints are disconnected or the duct tape has peeled away. To find smaller leaks, make sure your system is running, and then take a lighted matchstick or candle and let the smoke run over the duct joints. If you notice the smoke blowing away or getting sucked in, then you have a leak.

Step 2 - Use Tape or Caulk to Seal

After you've located the problem areas, the next step is to seal up those leaks. There are two methods you can use to accomplish this. The easiest way is to use aluminum foil tape to seal up any cracks or gaps in the duct. Make sure you select a high temperature tape and never use ordinary tape. (Actual "duct tape," is not suggested for sealing duct joints.) Before you place the tape on the duct, it's a good idea to wipe off any dust present on the duct work. This will help ensure a clean and lasting seal.

The second method used to seal duct work involves caulking. Caulking is ideal when working with flat, rectangular duct work. To start, simply clean any dust or debris from the duct and squeeze out a bead of the silicone caulk, making sure to cover both sides of the joint. To ensure a long-lasting bond is created, you can spread the caulk across the ducting edge with your finger.

Step 3 - Inspect the Entire Ducting System

Once you've successfully sealed one duct, then it's time to move on and repeat the process, as it's not uncommon to discover multiple places in your duct system that need repair. Remember to inspect vent openings and places in your HVAC system where connections are made. It may seem like a lot of work, but inspecting the entire system will certainly pay off in the long run. If you're unsure if you've fixed all the leaks, one thing to look for is how well the HVAC system performs after the repairs as compared to before. If you see a clear improvement in energy efficiency, then you can feel confident that you have covered the biggest leaks.

There are a few things to keep in mind when repairing leaky duct joints. As the duct system runs throughout a home, there may be places that prove impossible to reach. If this is the case, and you suspect a leak in these hard-to-reach locations, then you might consider calling in a professional. Additionally, alternative methods to sealing leaky joints include the use of mastic and fiberglass mesh tape. While a little trickier to apply, this method will result in a more permanent solution to a leaky duct issue. Furthermore, if you want to improve the efficiency of your duct beyond simple repairs, then consider insulating your ductwork. Insulation will help prevent air leaks and help your home become even more energy efficient.