GET A PROFESSIONAL!

Because of the possible effects that changing the duct leakage pattern can have on indoor air pollution, you should not attempt to repair duct leaks. Suppose, for example, that you find several disconnected duct joints in your supply system. Wouldn't it make sense to hook them back up? Probably it would, but if the return system has leaks you can't fix, you might end up with an unbalanced system like the one in Figure 4.

There are many variations on this theme, but this illustration shows that safe duct repairs require a licensed heating, ventilating, and air-conditioning contractor to repair ducts. Try to find one that has sent their technicians to a good duct-repair school. Such courses typically i involve at least a week of intensive training.

One of the special tools that would be used by a technician is a blower door- a temporary barrier set up to cover an open outside doorway, in which is mounted a fan that is used to apply a small pressure to the house. The main use of the blower door is to test for air leakage in the house, but it is also used in duct leakage tests. One test for duct leakage involves simultaneously pressurizing the house with the blower door and the ducts with a smaller version of this device. Another test uses the blower-door result plus some simple pressure measurements to estimate duct leakage.

A contractor's representative or service technician should be able to answer the following questions to your satisfaction:

• How do faulty duct systems lose energy? (They should know at least as much about the subject as you do now.)
• How would you test my duct system to see if it needs repair?
• What would you do to fix it if you find that work is needed?

Our discussion of health issues should not deter you from doing something about duct leakage, which could be contributing to a potentially serious health problem right now and you might not know it. When a qualified professional repairs your duct system, it is quite likely that the quality of your indoor air will improve. A qualified practitioner will perform the tests necessary to make sure that no problems are created where they didn't exist before.

OPPORTUNITIES IN NEW HOMES

We have discussed the ductwork in existing homes. If you are building a new home, you're in luck! You have the opportunity to make sure that the duct system will deliver top-notch comfort and efficiency by specifying to the builder that you want a leak-free, insulated duct system.

Even better, discuss with your builder the option of locating the ducts within the conditioned space and hiding them so that they don't show. It is possible to box in ductwork installed near the intersection of a wall and the ceiling, or to use other builders' tricks so that the raw duct materials will not be visible. It will be easier to do this than might at first appear because an energy-efficient duct system in an energy-efficient home can be less bulky than a standard duct system. This is because the amount of heating and air conditioning needed will be much less than in a standard installation. This will permit the use of a smaller furnace and air conditioner, which require a smaller amount of air flow in the duct system.

When it is possible to reduce the size of the duct system and the central unit, you save on equipment, materials, and installation costs, possibly enough to pay for the cost to hide ducts that are located within the conditioned space. In that case, energy savings will start to flow immediately. Even if some additional cost is involved, a duct system properly installed inside the conditioned space is energy-loss free and will likely be one of your best investments.

FOR FURTHER INFORMATION

The first two references below are readable guides requiring no specialized knowledge, although the professional can pick up quite a bit from them, too. The others are really intended for the professional, but could be a next step for the homeowner who becomes deeply interested in the subject.

Home Energy Magazine, Special Issue-Ducts Rediscovered.
September/October 1993. 2124 Kittredge Street, No. 95,
Berkeley, CA 94704.

This Old House; Heating, Ventilation, and Air Conditioning.
Trethwey, Richard. Little, Brown. 1994

Duct Design for Residential Winter and Summer Air Conditioning and Equipment Selection (Manual D).
Air Conditioning Contractors of America,
1513 16th Street, N.W.,
Washington, DC 20036.

Flexible Duct Penunnauce and Installation Standards.
Air Diffusion Council,
One Illinois Center, Suite 200,
111 East Wacker Drive,
Chicago, IL. 60602-5398.

A Guide to Insulated Air Duct Systems.
North American Insulation Manufacturers Association,
44 Canal Center Plaza, Suite 310,
Alexandria, Va 22314.

Installation Standards for Residential Heating and Air Conditioning Systems.
Sheet Metal and Air Conditioning Contractors' National Association, Inc.,
4201 Lafayette Center Drive,
Chantilly, VA 22021.

Energy-Efficient Design of New Low-Rise Residential Buildings.
Standard 90.2-1993.
American Society of Heating, Refrigerating, and Air Conditioning Engineers,
1791 Tullie Circle, N.E.,
Atlanta, GA 30329.

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