Duct Tape Story Still Unravelling

It seems that your experiments at Lawrence Berkeley National Laboratory are based largely upon an assumption that the use of clamps is not prevalent. UL does not agree with this assumption, since clamp usage plays a major role in the acceptable performance of a UL-listed air duct construction. Clamp use not only is required as a part of the UL certification of air ducts but also is prevalent throughout installation standards (i.e., Air Diffusion Council). Also, the codes require the air ducts and joints to be installed in accordance with the listing and accompanying installation instructions. Therefore, the clamps are an integral part of the air duct system construction. Since tapes marked 181B-FX are intended for use with clamps and UL-listed air ducts, your testing without clamps should not have been "tied" to the UL certification of the air duct system construction.

Based upon these facts, there are some portions of your article that are not accurate and with which we are not in agreement. We appreciate the opportunity to review your article, and we recognize your efforts to enlighten others about air duct systems and closure means.

Dwayne E. Sloan, Staff Engineer
M.T. Cunningham, Engineering Group Leader
Underwriters Laboratories

Iain Walker holding a locking duct that needs no tape sealant.

Authors Max Sherman and Iain Walker respond: While it is true that the UL test requires clamping, such clamping is rarely done in the field, at least in the construction types we have seen. While we have seen installation literature (from ADC, for example) that indicates clamping is to be used, none of the tapes we purchased (or were sent) came with instructions.

We believe the 181B-FX tapes (indeed all of the tapes) would do better if clamped, because the failures would take longer to become apparent. They all would probably also have done better on a flex duct-to-collar type of joint rather than a finger joint. Our objective, though, was accelerated testing of the sealants to determine relative performance, and from that perspective our tests were accurate. As we infer from your comments, our results may lead to potential changes in installation practices, but we did not dwell on that issue in the report.

I found your article "Can Duct Tape Take the Heat?" on the Internet after reading about it in today's Times-Union in Jacksonville, Florida. I am not surprised to learn that duct tape doesn't last on heat and air ducts (even though I love the stuff and always have a roll in my car--you never know when you'll need some). My question is: Would duct leakage account for the dripping from my ceiling vents in the summer months (condensation?) when I have my air conditioner on in the hot, humid conditions in Florida?

My husband and I built our home approximately seven years ago and we have four a/c units (the house is just over 6,000 ft²). We moved into the house in December, and all was well. Then during the first summer here we began having a drip problem from about a third of the a/c vents (two a/c units).

I called the company that installed the a/c (and ductwork), and now it is seven years later and still the problem is not solved. I have mildew on the ceilings around the dripping vents. Just yesterday (before I read the article) I contacted my a/c company again and asked to have someone do something about it. They don't seem to know what to do. The repairman came half an hour ago and said, "I'll send a duct man. I don't know anything about ducts."

I just want to figure out what to do about the leaking! Any ideas?

Thanks,

Chris Orta
Jacksonville, FL

I am a long distance runner. I am also prone to blisters and as such have taken to carefully applying layers of duct tape to my toes and the bottom of my feet before my 50-mile runs and my 100-mile attempts. I have found that 3M duct tape works the best, and that if I carefully clean my feet with alcohol and gauze pads, let it dry, and then spray on a product called Liquid Bandage, it works better.

However, it does not work well on a hot day! There must be something better I could be using. Any suggestions?

Thanks

Ross D. Lewis, Jr.
Los Angeles, CA

I recently read an article in the L.A. Times about your test on duct tape. If it doesn't work, what is the BEST tape that will work? Also, how did this tape get its name if it is not reliably used to seal ducts?

Steve Latshaw
Los Angeles, CA

This article is incredibly illuminating! We remodeled our house following the Loma Prieta earthquake, installing all new ducting and a new +90 high-efficiency, condensing furnace. I thought I had gone crazy when in less than three years the main duct in the furnace room fell off the connecting sheet metal branch. We only noticed it because it was VERY COLD in the house, but we had no idea how long it had been like that.

After repairing it with additional duct tape and wrapping that with zip ties, I went under the house and discovered that at least half of the other ducts had FALLEN off the registers! I made the same type of repair, wrapping with more duct tape and then fastening the duct tape with zip ties. I also carefully restrapped the ducts so that there was less weight on the registers, holding them in place. Unfortunately, I had no way to get to the ducting that was in Sheetrock and then connected to registers.

We just recently sold that house, and the inspector made mention of two registers that did not have air coming out when the furnace was on. How curious! So much for spending huge amounts of money on a high efficiency furnace!

Thank you for your work! I am now in a brand new home and am about to go under the house and rewrap the duct tape with clear plastic shipping tape. And now I know to keep a good eye on this kind of a problem. And yes, I did make sure the new house had a +90!!

Michael Light
Aptos, CA

Editor's note: There has been a great deal of reaction to Sherman and Walker's duct tape research results. To respond to requests for more information, the scientists have put up a duct tape page on their Web site. The address is http://ducts.lbl.gov/ducttape.

On the Question of Kilowatts

The total annual energy costs for this all-electric house, which includes a private well for two families, averages 16,311 kWh. The energy used for heating, cooling, filtration, and ventilation is about 7,666 kWh. The 1,157 kWh mentioned in the article is the power necessary to run the energy recovery ventilator motors for one year and is included in the 7,666 kWh total for space conditioning.

Additionally, the ventilation rate equals 0.65 air changes per hour. I wanted to ventilate at that rate to maintain a VOC level in this new house such that I could not detect the smells when I entered from outside. Achieving this healthy ventilation rate was not expensive. We use 166 kWh per month, which costs $9.17.

Although "super housing" is possible, most of us will spend most of our life in a more common type of shelter. That being the case, we should expect "common housing" to perform to its full potential.

Bruce Davis
Raleigh, NC

Errata

In "Putting the Byte Into Your Analysis Toolkit" (Sept/Oct '98, p.25) we published a list of energy analysis software contacts (p. 31) and did not include one of the best energy analysis sites on the Web. The Home Energy Saver, developed by Lawrence Berkeley National Laboratory, is available at http://eetd.lbl.gov/hes/.
 
 

Home Energy can be reached at: contact@homeenergy.org
Home Energy magazine -- Please read our Copyright Notice