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National Comfort Institute
Pacific Northwest National Laboratory
Contracting Business/Kelly Faloon
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Manhattan darkened by smoke from Canadian wildfires.

Duct Design Trends

Sept. 1, 2002
Question 2: Are parts of the walls or floor cavities used as ducts? For example: spaces between ceiling and floor joists or internal wall stud spaces.
Question 2: Are parts of the walls or floor cavities used as ducts? For example: spaces between ceiling and floor joists or internal wall stud spaces. Usually, these are return air flow paths to the fan. You can look through the grilles and see that the building cavity has been used and there is no duct connected to the other side of the grille. Perhaps you don’t want homeowners peering through the grilles to determine if your HVAC company used “building cavities” for ductwork. However, if they land on the Environmental Protection Agency’s (EPA’s) Energy Star® website to read up on duct design, they’re likely to find this question, among 11 others, that help them determine whether their home is a candidate for the new Energy Star ducts program. Face it. Consumers are becoming more educated about their comfort systems and are beginning to understand that the system includes the air distribution ductwork. What Are Energy Star® Ducts? The Energy Star program helps consumers recognize energy-efficient products that save money on their utility bills. The U.S. Environmental Protection Agency (EPA) and the Department of Energy (DOE) created the Energy Star program as the symbol for energy efficiency because of the direct link between wasted energy and air pollution. Manufacturers and builders voluntarily display the label on products and new homes, including heating and cooling equipment, that meet high efficiency Energy Star guidelines. The new Energy Star duct specification was designed for existing homes. As part of the program, a knowledgeable contractor performs tests on the duct system to determine whether a home will be more comfortable, more efficient, and safer by having all leaks in the ducts sealed. According to the EPA, duct sealing and testing ducts will help to use energy more efficiently and will, in return, reduce the amount of carbon dioxide that homes generate in the burning of fossil fuel. In addition, sealing ducts will help control chemical pollutants, mold, dust, and combustion gases that can enter the home and make families less safe. Properly sealing the leaks in a duct system can boost efficiency and lower energy bills. The typical family could save up to $140 annually. Leaking ducts can decrease the overall efficiency of the heating and cooling system by as much as 20%. Several utility program in various state’s are expected to adopt the Energy Star duct program specifications as guidelines for consumer programs. It’s Not Just About Selling and Installing Boxes Anymore As evidenced by the EPA’s Energy Star duct program, the air distribution component may be the most important aspect of the total comfort equation. In a forced air central heating and air conditioning system, the duct system is the network that distributes air throughout the home. Ducts are essentially a series of large pipes or tubes that are usually hidden from view, located within ceilings, walls, or floors. The duct outlets, which are covered with registers or grilles, are visible from the living area. However, ducts can sometimes be seen in non-living areas, such as the attic or garage. The duct system works hand-in-hand as part of the heating and cooling system to provide proper airflow for heating and/or cooling. The equipment conditions air and delivers it to the living area through supply ducts. Air is also sent back to the equipment through return ducts. Studies show that most duct systems contain significant leakage, causing a major portion of the conditioned air to be wasted. The energy used to warm or cool this air is also wasted, requiring occupants to spend more money on utility bills to maintain their desired comfort level. Significant amounts of money can be saved by improving a system’s efficiency by having a duct system sealed, insulated, or replaced. Leaky or improperly sized ducts can affect a home’s comfort. Sealing and insulating ducts increases the ability of the heating and cooling system to evenly heat and cool all of the rooms in a structure. Sealing Leaky Ducts May Seem Easy, But It’s Not Working on duct systems will often change the pressure distribution in a home, sometimes dramatically. To maintain proper comfort and air quality it’s important to maintain a proper balance of supply and return air. An imbalance can create a pressure difference in a building that can introduce pollutants into the air such as fumes from chemicals, insulation particles, mold, and dust. Sealing a visible leak may seem easy enough, but doing so could change the balance of incoming and outgoing air. This could greatly reduce the occupants’ comfort, lessen system efficiency, and introduce pollutants into the living environment. An imbalance can also cause safety concerns by creating a backdraft condition (when combustion gases like carbon monoxide flow back into the building, instead of out the flue) with other combustion appliances such as hot water heaters and fireplaces. Before sealing obvious leaks in a duct system, you should evaluate the entire heating and cooling system. Check out all the ramifications of your actions before launching a duct sealing campaign. Tools are available for contractors to test and balance air distribution systems. Diagnostic tools should be used only by individuals who have a working knowledge of safety issues and who take precautions to deal with them. (See Tools of the Trade for a listing of some that are available.) More To It Than Meets the Eye The Energy Star duct program focuses intently upon duct sealing with a lesser emphasis on the intial design. However it goes a long way toward educating the public about the importance of properly designed duct systems. The program helps HVAC contractors justify to customers the need for testing the performance of the air distribution system. At the Energy Star website, contractors will find the Duct Investor software tool that allows them to enter information about the type of duct system and the tested duct leakage. The software outputs results including estimated costs and return on investment for any duct renovation. Any questions about the website or the program can be directed to 888/STAR-YES.