Fact: Typical duct systems lose 25-40% of the heating or cooling energy put out by the central furnace, heat pump, or air-conditioner. Homes with ducts in protected areas like basements lose somewhat less, whereas systems such as attic ducts in hot, humid climates often lose more. That figure can double in homes where ducts are not insulated because heat is also lost through conduction. You can:

  • Reduce your energy consumption 25-40%.

  • Improve your home air quality.

  • Reduce safety concerns from pressure imbalances.

Best Features: Energy savings, health, and safety offer compelling reasons for a duct check-up. Duct leakage can depressurize your home, resulting in back drafting of flue gases from combustion appliances, flame rollout on water heaters (a fire hazard), and an accelerated pollutant rate of entry into your home. Use common sense for safety--guard against falls; wear protective gear; avoid opening or probing into electrical devices, wires, and connections; and don't touch ducts without first holding your hand above them to see if they are hot.

  • Properly sealed ducts will result in the following best features:

  • Improved energy efficiency in forced air systems.

  • Identified pressure imbalances caused by an ineffective duct system.

  • Reduced flow of pollen, dust, and other airborne particles in your home.

  • Decreased humidity, which will lower mold, mildew, and condensation.

  • Minimized vapor from household cleaners, vehicle exhaust fumes, and other toxic materials stored in attics, basements, and garages.

  • Reduced likelihood of soil gas (i.e., radon, methane, pesticides) penetration into your home.

  • Lowered possibility of fumes from combustion appliances.

Save Money: Much of the appropriate retrofit work involves doing things that were missed or were done improperly by untrained technicians who did not understand the issues involved or did not consider them part of their job. Working with a trained professional will help maximize your home's energy efficiency, while improving air quality and reducing safety concerns. Follow these tips to save money in the process:

  • Make a rough sketch of your system, beginning with your central heating unit.

  • Locate and clean the filter in the central fan unit or return register.

  • Hire a trained professional to check pressure balances.

  • Insulate ducts in attics and unconditioned spaces first.

  • If ducts are located in the basement, insulate walls first.

  • Reconnect ducts that have fallen away from one another.

  • Repair visible holes and seal joints with silicone caulking or cement with mastic. Do not use duct tape for longer-term repairs.

  • Identify and repair blind alley ducts.

  • Check for inadequate duct work.


Find It: You should not attempt to repair duct leaks yourself because changing the duct leakage pattern can increase indoor air pollution, which must be mitigated in some other way. Safe duct repairs require a licensed heating, ventilation, and air-conditioning technician. Try to select a company whose employees have had at least a week of intensive training in the use of blower doors and other duct leakage identification techniques.

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Figure 16

Ducts-Out of Sight, Out of Mind: One of the most important systems in your home, though it's hidden beneath your feet and over your head, may be wasting a lot of your energy dollars. Your home's duct system, a branching network of tubes in the walls, floors, and ceilings, carries the air from your home's furnace and central air-conditioner to each room. Ducts are made of sheet metal, fiberglass, or other materials.

The unsealed ducts in your attics and crawl spaces lose air-uninsulated ducts lose heat, wasting energy and money. Sealing your ducts to prevent leaks is even more important if the ducts are located in an unconditioned area such as an attic or vented crawl space. If the supply ducts are leaking, heated or cooled air can be forced out unsealed joints and lost. In addition, unconditioned air can also be drawn into return ducts through unsealed joints. In the summer, hot attic air can be drawn in, increasing the load on the air-conditioner. In the winter, your furnace will have to work longer to keep your house comfortable. Either way, your energy losses cost you money.

Unfortunately, many duct systems are poorly insulated or not insulated properly. Ducts that leak heated air into unheated spaces can add hundreds of dollars a year to your heating and cooling bills. Insulating ducts that are in unconditioned spaces is usually very cost effective. If you are buying a new duct system, consider one that comes with insulation already installed.

  • Although minor duct repairs are easy to accomplish, ducts in unconditioned spaces should be sealed and insulated by qualified professionals using the appropriate sealing materials. Here are a few simple tips to help with minor duct repairs:

  • Check your ducts for air leaks. First look for sections that should be joined but have separated and then look for obvious holes.

  • If you use duct tape to repair and seal your ducts, look for tape with the Underwriters Laboratories logo to avoid tape that degrades, cracks, and loses its bond with age.

  • Remember that insulating ducts in the basement will make the basement colder. If both the ducts and the basement walls are uninsulated, consider insulating both.

  • If your basement has been converted to a living area, install both supply and return registers in the basement rooms.

  • Be sure a well-sealed vapor barrier exists on the outside of the insulation on cooling ducts to prevent moisture buildup.

  • Get a professional to help you insulate and repair all ducts.

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