Why Duct Tape Should Never be Used to Seal Air Ducts

“Of all the things we tested, only duct tape failed. It failed reliably and often quite catastrophically,”

That was the result of a test from Berkeley Lab to see which sealants properly sealed air ducts.

“Surely that can’t be!” you’re thinking, “Duct tape has so many uses, and it’s got “duct” in the name for goodness sake!”

But it’s true. Despite its name, duct tape really shouldn’t be used for sealing ducts. In fact, it’s the worst solution when compared to other sealants. But why?

Before we answer that, let’s explore how duct tape got its name.

Why is it called duct tape anyway?

According to Forbes, duct tape was invented during WWII and called “duck tape”. The military used this tape (back then it was green) to keep moisture out of ammunition cases.

But back then, just as people do now, the military discovered that duct tape had a variety of other uses, such as quick repairs.

After the war when the housing market was booming, the tape became available to civilians, and some manufacturer started selling it as a means to connect heating and air conditioning ducts.

So, in order to make the tape match with the ducts, the color was changed from an army green to the familiar silver color we have today. And so it was called “duct tape.”

However, duct tape doesn’t adequately seal the duct joints in the long run.

The Berkeley experiment

In 1998, Lawrence Berkeley National Laboratory (LBNL) researchers performed a 3-month experiment to see if duct tape, alongside 31 other sealants, could hold up to typical conditions found in air ducts.

To simulate these conditions, hot air (167 F) and cold air (53.6 F) was forced through several air ducts, each duct using a different type of sealant to keep the air inside.

They also wanted to simulate attic heat during the summer. So they performed a “bake test” in which the sample joints were baked at temperatures of 140 to 187 F.

The results?

The researchers found that the duct tape would either allow too much air to escape or it would just fall right off after a few weeks or months.

The reason?

Iain Walker, one of the researchers, said, “We think that heat degrades the glue, and that’s what’s killing the duct tape.”

What should I use instead of duct tape?

The researchers recommended sealing ducts with mastics, which are gooey sealants that are painted on and allowed to harden.

Berkeley researcher Max Sherman did say “while duct tape may not last long as a sealant, in the short run it is strong, sticky, and fairly easy to use.”

So, if you need to hold a couple things together, duct tape can be great solution. But to seal your ducts for more comfort or energy efficiency, call a professional or use mastic sealant instead.

Need ducts sealed in your Southern California home? Follow our guide on finding leaks and sealing them, or contact us online to schedule a time for service.