Why
Central air conditioning and heating are the top energy consumers in California homes, so ensuring the efficiency of your entire HVAC system can yield big improvements in energy efficiency. When we think about saving energy, we commonly focus on the furnace and air conditioner units, but a leaky duct system can reduce your climate control system's efficiency 20% to 30%. These leaks can bring unwanted dust, unconditioned outdoor air and humidity into living spaces-and take money straight out of your wallet.
Recommendation
If your home is over seven years old, have your ducts professionally tested by a certified Home Energy Rating System (HERS) technician and have them repaired if they are excessively leaky. Duct testing is also advisable whenever heating and air conditioning units undergo a diagnostic tune-up. Duct testing is recommended for any building where a forced-air heating or air conditioning system is used.
“Some of the houses I go into might as well
not have a heating or air conditioning system.
They are leaking so badly we can barely get a reading.” (Rick
Lee, HomeEnergyRatingService.com)
Description
Duct pressure keeps heated or cooled air flowing evenly to the all registers (air vents) in the system. Without proper pressurization, registers nearest the furnace or air conditioner receive most of the conditioned air; distant registers receive very little airflow. If the return ducts are leaky, contaminated air from damp basements, wet crawl spaces, and attic areas that may contain animal droppings or hazardous insulating materials may infiltrate your system. Cold, wet air pulled into your system from leaking ducts condenses, and condensation can lead to mold growth. Mold growth can lead to health problems and more.
The most reliable way to find out if your ducts are leaking is to have a duct test performed by a qualified technician using the proper test equipment.
The building code now requires independent verification of proper duct installation in new buildings that have forced-air heating or air conditioning, when a new central air conditioner or furnace is installed, or in renovations that will add or change over 40 feet of ducts.
Home Energy Rating System (HERS) raters are certified by the California Energy Commission as qualified to perform energy rating services, including accurate duct leakage tests.
To test duct integrity, HERS raters seal the duct registers and returns (vents where the air goes in or out), then pressurize the system using a calibrated blower to blow air into the duct. A probe placed inside the duct measures the airflow and indicates the amount of leakage. Results can range from detecting small leaks to discovering that entire duct sections have become disconnected from the system.
When duct testing reveals leaks in new construction, it is the contractor's responsibility to fix the leaks. Homeowners can repair some types of leaks found in older buildings-reconnecting ducts that have become completely disconnected, for example. If you decide to repair your own duct system, you should always wear a respirator when working in an attic space. If your system requires more than simple repairs, it will be most efficient and effective to hire an experienced heating and air conditioning contractor to seal, repair or replace ducts.
Other Ways to Improve Duct Performance
Insulate Ducts: Insulate all ducts located in unconditioned areas (attics, crawl spaces, exterior walls) to R-6. For ducts located within the conditioned envelope, insulating to R-4.2 is adequate.
Keep Registers Clear and Clean: Keep furniture and other objects clear of all registers (air vents) to avoid blocking the airflow, and vacuum registers to remove dust buildup.
In buildings with more than one story, focus on repairing ducts in the roof ceiling space first. Leaking ductwork in a ceiling space between floors is not as bad as leaking ducts in the roof ceiling space or in an unconditioned zone (like the attic) with an exterior or roof exposure. The temperature difference from the adjacent conditioned spaces will be significantly higher in spaces just under the roof, so there will be a greater impact on the equipment efficiency.
Very important: Ducts in homes built prior to the mid-1970s are very likely made from asbestos, a hazardous material. Do not touch or attempt to repair ducts that contain asbestos! Because asbestos is a hazardous material, ducts that are constructed, insulated or sealed with asbestos are not tested by HERS raters. Asbestos abatement companies should always be contracted to remove asbestos ducts.
Crushed asbestos duct.
Don't Use Duct Tape?
Late in 1998, scientists at the Lawrence Berkeley National Laboratory made a startling discovery: Ever-popular duct tape was useful for hundreds and hundreds of tasks, but holding ducts together wasn't one of them.
Over three months, researchers tested duct tape and 31 other sealants under accelerated laboratory conditions that mimicked long-term use in the home. They heated air to nearly 170 degrees and chilled it to below 55 degrees before blasting it through ducts. They baked ducts at temperatures up to 187 degrees to simulate the oven-like conditions of a closed attic under a hot summer sun.
Of all the things they tested, only duct tape failed-and they reported it failed reliably and often quite catastrophically.
Instead of using duct tape, the researchers recommended sealing ducts with mastics, gooey sealants that are painted on and allowed to harden. Metal ducts should be held together with sheet-metal screws; flexible duct connections should be secured with metal or plastic bands. (California Energy Commission)
