Archive for the ‘Heating and Ventilating (HVAC)’ Category

Duct tape should not be used to seal ducting

Tuesday, August 17th, 2010

When conducting an inspection of the components within a crawl space, which includes a general observation of the ducting for the heating and cooling system of a residence, I sometimes come across sections of ducting that are disconnected at the joints, or very poorly sealed. I don't make an attempt to remove any ducting insulation that is perfectly intact in order to view the joints in the ducts. In instances where the insulation (if present) is loose, damaged, or missing, and the joints are clearly viewable, I will have a look at random samples of these joints. I commonly find that duct tape was used to seal the joints, and the tape has become very frail and sometimes so damaged that there are joint separations which allows heat or cooled air to treat the air within the crawl space. This means less treated air into the rooms of the house which in turn is very inefficient and costly.

As the name implies, one would naturally expect to find Duct tape used to seal the joints in the ducting for heating and ventilation in buildings, however, it is not intened to be used for such purpose, and is not what a property inspector wants to find when examining the ducting.   Duct tape   is a polyethylene, reinforced, multi-purpose pressure sensitive tape with a soft and flexible shell and pressure sensitive adhesive. It is generally silver or black in color but many other colors have recently become available, and can be purchased at hardware stores, and some drug stores and super markets. It has many uses, and can be found among the tool collection of most home owners.

Duct tape was never intended to be used to seal ducting, Originally developed in 1942, during World War II as a water resistant sealing tape for ammunition cases. Permacel, then a division of Johnson & Johnson, used a rubber-based adhesive to help the tape resist water and a fabric backing to add strength. It was also used to repair military equipment quickly, including jeeps, firearms, and aircraft because of these properties.

To provide lab data about which sealants and tapes last, and which are likely to fail, research was conducted at Lawrence Berkeley National Laboratory Environmental Energy Technologies Division. Their major conclusion was that one should not use duct tape to seal ducts (specialty tapes are available for this purpose). (They defined duct tape as any fabric-based tape with rubber adhesive.) The testing done shows that under challenging but realistic conditions, duct tapes become brittle and may fail. It is very common for me to find duct tape that has become very frail, and in most instances, is allowing a significant amount of heated or air conditioned air to escape the ducting instead of through them to the registers in the room of the building. This means the system is not very efficient, and is costing the property owner money to condition the air in either the attic or the crawl space under the building, (where ever the systems ducting is located). Commonly duct tape carries no safety certifications such as UL or Proposition 65, which means the tape can violently burn, produce toxic smoke, ingestion and contact toxicity, irregular mechanical strength, and low life expectancy for the adhesive on the tape. Its use in ducts has been prohibited by the state of California, and by building codes in most other places in the U.S. However, metalized and aluminum tapes used by professionals are still often called "duck/duct tapes".