News & FAQ

How to Properly Seal Ventilation Ducts

11/19/2015

Valerie Johannsen People & Brand Manager

You already know that leaks in your ventilation system can let out vital air into spaces that don’t need it.  And that leaks add to the strain your furnace or air conditioner endures to control the climate of your home.  So let’s say that you’re working in your attic, or simply bringing out decorations at the change of the season when you feel a draft coming from a nearby duct.  A quick examination shows tear, hole, or even just a seam that’s come loose and is now leaking into the attic (or any space for that matter).

Though this seems like a simple fix with a sturdy roll of duct tape (it’s even in the name, right?) duct tape is only a patch job and isn’t an effective method of fixing the problem.

Tape is Temporary

While tape works as a temporary measure, it lacks staying power.  Duct tape and foil tape both lose their adhesiveness relatively quickly (duct tape begins to fall off after about a month).  Instead, you need something that’s applied and will last at least as long as the ventilation ducts themselves will.  A quality job uses mastic instead of any kind of tape.  It takes a little longer and is a little messier during application, but the tradeoff is that it lasts longer and is a far more effective method of sealing your ventilation system.

What is Mastic?

Mastic is an adhesive resin use as a commercial sealant.  Unlike expanding foams, glues, and other sealants or adhesives, mastic doesn’t harden.  With a consistency similar to peanut butter, it can be somewhat difficult to work with if you aren’t used to it.  Gloves and old clothes (or a Service Legends uniform if you’d like our help) are ideal because it will get everywhere and skin contact is inadvisable due to its staying power.  Once the seal is made, wrapping the joint or seam in mesh tape should be the finishing touch.

Of course, larger cracks and seams (1/16 or 1/8 of an inch) will need more work.  The repair itself will require fiberglass mesh to cover the opening.  The more damage you see, the more complicated the repair will be.


When you call Service Legends, not only can we repair any ventilation leaks you know of, we can find leaks and cracks in the space between walls.  Every single leak in your system is wasted energy, which means wasted money for you.  Call us today to see how we can help you identify and seal every leak in your system with more than just a simple duct-tape patch job!

Thank you for making Service Legends the #1 provider of residential heating and air conditioning in the Des Moines area. A live and friendly customer care representative is ready to take your call 24/7 at 515-COMFORT (515.266.3678).

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