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Battle of the Tape: Duct Mastic vs. Foil Tape

Ducts within your home can spring leaks for a wide variety of reasons, and at any time, making it a somewhat tough problem to lookout for. That’s why it’s important to have your HVAC system regularly maintained. Still, if you suddenly have a higher-than-average energy bill, your air conditioner or furnace seems to have to work harder to cool or heat your home, or some rooms are noticeably different in temperature or stuffier than others, you may have leaks in your ducts. These leaks within the home can be costly, make your appliances wear out faster, make your home less comfortable, and waste energy over time. In fact, leaky ducts can be one of the largest energy wasters in the home that hinders your attempts at cutting down your energy bills!

Luckily, the ducts that run through your home can be sealed with either foil tape or duct mastic, and every DIY master or contractor has their own preference for what they use when working on residential ducts. Both of these options have their benefits and drawbacks, and just like any project, a professional assessment can go miles toward ensuring the work is done right and will last well into the future. Let’s take a look at the pros and cons of both approaches.

Duct Mastic

Duct Mastic Duct mastic can be easily applied using a paintbrush and is readily available at most home improvement stores. It is a gooey substance that provides good coverage and can be applied generously to duct joints and leaks. When used appropriately (not spread too thin) duct mastic is a great option for ensuring that the seal will not fail over time. Quality mastic will last as long as your duct system. Mastic is also a good choice for those hard-to-reach areas, and those sharply angled duct joints. There is also no risk of mastic delaminating and stripping off over time.

Foil Tape

Tapes Flat metal tape coated with an adhesive is good for filling holes and gaps. Foil tape should only be used for sealing. Quality tapes can be hard to find and must often be purchased at specialty heating stores. Purchasing low quality tapes from Home Centers is not recommended because there is a high risk of failure after only a few years. Professional quality tape will stand the test of time. Tapes are much cleaner than mastic, but is a bit more expensive to purchase. For long sections of hard, round ductwork, taping can be an acceptable practice, but irregular surfaces and dirt or dust can compromise the application.

A Word of Caution The term “duct tape” is quite misleading. Although the name of this product makes it sound perfect for the job at hand, never seal ducts with duct tape. Duct tape is not approved for use on ducts and, despite the fact that it works great for a variety of heavy-duty projects, doesn’t stand up to the conditions of an HVAC system. At Murray Lampert Design, Build, Remodel, we prefer to use duct mastic to seal and repair ducts. We like it because it stands the test of time and makes it easy to fill in those irregularly shaped areas of ductwork. If you have a leaky duct to repair, consider your unique circumstances and which material you feel most comfortable working with. A word of advice with either option: choose a high-quality product. For quality HVAC installations and service, I recommend Mauzy Heating & Air Conditioning.


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Gregg Cantor, a third generation contractor and owner of Murray Lampert Design, Build, Remodel has successfully remodeled thousands of homes in San Diego County. Gregg's is experienced in all phases of construction and home remodeling including design development, project management, best building practices, code requirements, and contract law. He also writes articles for examiner.com and is co-host of The Home Pro Show Saturday's at 9 a.m. to 10 a.m. on A.M.600 KOGO San Diego. Follow Gregg's posts.

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