Lost in Thin Air

You may have read or heard that, for an "average" house, 20 to 30 percent of the energy used for heating and cooling is lost through the ductwork. Most of this loss is through small gaps in the joints of the ductwork of forced-air distribution systems. In a forced-air distribution system the duct runs do not merely pass the air blown into them by your furnace's air-handler, they are actually pressurized. Air not only rushes out these registers, it is forced through the hundreds of seams and gaps of the typical duct system. For this reason, it is the imperative of good installation practice to seal every joint and seam with a tape or adhesive caulk.

Don't use duct tape for this job!

The duct tape that has become a cultural icon-that grey, gummy stuff-is surely one of the twentieth century's all-purpose miracle remedies. I have appreciatively availed myself of the Johnny-on-the-Spot characteristics of duct tape to patch old jeans torn at a construction site, and to reinforce a sledge hammer handle that had started to split before the job was finished. Other fellas have taped it around their shoes to keep the soles from flappin', or held a rusty bumper on their pickup truck until they got around to buying some new bolts. Duct tape is great for stuff like this.

Now here comes the results of a high-tech study done by The Department of Energy at their Lawrence Berkeley National Laboratory. They taped up their system of test ducts with duct tape, clear tape, foil tape, mastics and injected aerosols. Then they pressurized their ducts with both hot and cold airflows. They also baked the ducts at temperatures from 140 to 187 degrees, simulating known attic conditions.

According to researcher Max Sherman of the Lab, "..of all the things we tested, only duct tape failed. It failed reliably and often quite catastrophically." It seems that heat degrades duct tape's glue, and then it falls off. Now, fellas in the construction trades have known this about duct tape for years. We're gonna have to call those guys at the lab and tell them what this stuff is really for. That bumper on my truck is still hangin' on!