How to Seal HVAC Duct Leaks—and Hidden Signs You Have Them

One of the best parts of my job is making simple changes and upgrades to people’s homes, be it to their windows, pipes, or their HVAC systems, to help them conserve more energy in a big way. I may not look like a stereotypical tree-hugger, but I really care about the environment. Of course, I also care about helping my customers save money.

So, what if I told you that you could be saving anywhere between $79 and $119 each month on heating and air conditioning costs? Sounds too good to be true, right? Actually, this could be a reality for many American households. So what’s draining these dollars? Leaky HVAC ducts.

Luckily, there’s a fairly straightforward solution for this—seal your HVAC duct leaks. So, in the spirit of saving big bucks and loads of energy, I’m going to help you figure out if your HVAC ducts are leaking, then share with you the best methods for sealing up those pesky, energy-wasting holes.

Signs You Have Leaky HVAC Ducts That Need to Be Sealed

Often, without us even realizing it, our HVAC system stops heating or cooling our homes efficiently, through no fault of the furnace or air conditioner. The Department of Energy estimates that a typical home loses 20-30% of its HVAC conditioned air as it makes its way through ductwork, escaping out through holes, leaks, and improperly connected ducts.

It’s easy to neglect your HVAC ducts. Out of sight, out of mind, right? But when you don’t properly maintain your ductwork, they may develop holes and gaps. Over time, when warm or cool air is constantly moving through the ducts, connections can naturally expand and contract. If duct connections aren’t properly sealed, air leaks out.

It isn’t always easy to see these leaks, so it’s important to know the signs that your ducts need sealing:

• Sign #1: Your energy bill is on the rise. The first indicator that your ducts are leaking will likely be seen on your energy bill. While you may not notice an abrupt spike, as leaks and gaps become bigger and bigger, allowing more conditioned air to seep out, you’re bound to see a gradual, but steady increase on your monthly bill as you lose energy efficiency.
• Sign #2: You notice uneven heating or cooling throughout your home: Do you ever notice that some rooms in your house just don’t seem to heat up or cool down like the rest of the house? If this is the case, it’s possible that the duct feeding into that room is improperly sealed and some air is escaping before it reaches the space. This problem could also be due to unbalanced ductwork, so make sure you call in a pro to diagnose this issue correctly.  
• Sign #3: Your home is abnormally dusty or stuffy. Sometimes, when a duct has a gap or improper seal or hole, dust on the outside of the ductwork gets inside and makes its way into our home. You’ll know that this is the case if sneezing fits become the norm. Another common problem is that ducts carrying exhaust leak air into the house. Not only will this make your home stuffy and stale, it’s not great for your health.

If you notice any of the above problems, it’s time to inspect your HVAC duct seal for leaks. Of course, I’d recommend that you call in a pro for this; working with ducts can be a mighty tricky task. Not only can ducts be hard to reach, the holes and gaps themselves can be nearly impossible to spot with an untrained eye.

Common Ways to Seal HVAC Duct Leaks (That May Not Work)

When I go into a home to seal HVAC duct leaks, I always start with a thorough inspection of the entire ductwork. I often see evidence that the homeowner has tried to seal the ducts themselves using all sorts of interesting methods—many of which I wouldn’t recommend using.

Here are some of the common methods I see being used to try to seal HVAC duct leaks, along with the benefits and drawbacks of each:

• #1: Duct tape – I can’t tell you the number of times I’ve seen shreds of duct tape hanging from the ductwork in a home. This is the one material that actually has no sealing properties, even if it meets UL 181 standards (used for rating duct sealants). Duct tape delaminates very quickly, and will really only provide a sub par seal for up to a month at most. While it may seem like a quick, easy, and cheap fix for leaky ducts, it is not a good choice to seal your HVAC ductwork with.
• #2: Foil tape – Similar to duct tape, and seemingly almost as popular for the task, foil tape is not a good option for sealing ducts. Like duct tape, it delaminates very quickly and often doesn’t stick well to the ductwork. It’s also fairly pricey so don’t go wasting your hard earned cash on this stuff, even if it has a UL 181 rating.
• #3: Oriented Polypropylene Tape (OPP Tape) – This tape has a strong acrylic adhesive and a film-backing, making it quite durable. OPP tape with a UL 181 rating works reasonably well on duct joints, as long as the joints are clamped and the outsides of the ducts are cleaned very well before application. However, this can be tricky for homeowners to properly apply on their own.
• #4: Mastic – Mastic is one of the best materials to seal HVAC duct leaks with. It can be great on its own for smaller gaps, and for bigger gaps it can be used in combination with fiberglass mesh tape. It’s long-lasting, creates a nice, tight seal, and you don’t have to clean the surface of the ducts before applying like you do with tape. The downside is that applying it is a messy job—especially for someone who doesn’t have experience with it. Even though it sounds like a DIY project, it’s best left to the professionals.

While it is possible to seal leaky ducts on your own, calling in an experienced professional and having them do it for you is a much better idea if you want to maximize your energy savings and save yourself some difficult labor. A professional has the equipment needed for the job, from assessing your entire HVAC system to testing the air pressure, locating every hole, and sealing them up tightly with the appropriate materials. When they’re through, they’ll test your system to make sure that the leaks are all properly sealed so that your HVAC system can run at peak efficiency, saving you money on energy bills and future repairs.

While it is possible to seal leaky ducts on your own, calling in an experienced professional and having them do it for you is a much better idea if you want to maximize your energy savings and save yourself some difficult labor.

The great thing is, if you decide to have your ducts inspected sealed by a professional, the cost of the service will pay for itself in energy savings before you know it. Then the only thing you’ll have to do is figure out how you’re going to spend that extra 79 or so bucks every month.

Seal those pesky leaks, holes, and improperly connected HVAC ducts to save money and energy. Contact the HVAC experts at Bell Brothers today to get your entire system running at peak efficiency, from compressors to plumbing, windows to insulation.

Image courtesy Unsplash user Kari Shea