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Jul 17, 2013 11:00 AM  PST  

GreenPointers: Heating & Cooling 

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GreenPointers: Heating & Cooling

Our series of GreenPointers provides helpful tips for a healthier, greener home in a variety of topics. Today's topic is Effective Duckwork.
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Most home heating and cooling systems include ductwork that circulates warm or cool air to each room. Ductwork that is properly designed and installed will help keep your home comfortable and healthy, and will help keep energy costs in check. Poorly designed and installed ductwork lowers heating and cooling system efficiency and capacity, and can contribute to poor indoor air quality and comfort problems.

Consider having ducts tested for airflow and leakage before and after any new work on a HVAC system. See our know-how feature on Building Performance to learn more.

These six strategies will improve ductwork effectiveness:

Step 1


  Insulate, to present building code levels or greater, any existing ductwork that is accessible and has no insulation or damaged insulation. To find out about local building code requirements, check with your town's building department, or with your builder, architect or other building professional.

Step 2


  Conditioned space refers to areas in the home that are heated or cooled. Ductwork that is installed outside of a home's insulated areas, such as above an insulated attic floor, can waste a lot of heating and cooling energy, even if the ducts themselves are wrapped with insulation. When installing new ductwork, it is good practice to keep the ductwork within the building's insulated envelope. Duct runs may be installed in closets, chases, and soffits purposefully designed to accommodate them, or they may be installed in an unvented attic that is insulated on the inside of the roof.

Step 3


  Gaps and separations in the joints between pieces of ductwork have been shown to allow, on average, 20% to 30% of heated or cooled air to leak out. That wastes energy. Also, leaky air ducts can cause negative pressure in the house, which can draw many outdoor and indoor contaminants into the home, including carbon monoxide from gas water heaters and furnaces. To prevent this, make sure all duct joints and seams are properly sealed. Don't use duct tape to seal ducts; it loses its effectiveness in a few years. To maintain a tight seal for decades, use a water-based duct mastic at every joint and seam or have professionally installed aerosol sealant sprayed into the ducts.

Step 3


  A low cost alternative to installing ductwork in conditioned space is burying the ducts in loose-fill ceiling insulation. This significantly improves the insulation value of ductwork compared to installing the ducts above the attic insulation. For this approach to be most effective, duct connections must be tightly sealed. Instead of suspending ducts from rafters or trusses, allow ducts to lay over ceiling joists or the bottom chord of trusses and blow insulation over them. To achieve moderate coverage, insulate to at least R-38. Using supply boots with side instead of top connections keeps ducts low and aids burial.

Step 3


  When a bedroom door is closed, it typically cuts off the return airflow path. This restricts air movement, leading to comfort problems and a pressure imbalance, with the bedroom pressurized and the rest of the house depressurized. This may cause infiltration of contaminated air from the attic or crawl space, or backdrafting of combustion appliances (for more about backdrafting, see our know-how feature on Carbon Monoxide and Combustion Safety). To prevent this problem, an HVAC contractor can install an additional return duct in the master bedroom and other large rooms that can be closed off with a door. Or jump duct or transfer grille can be installed between the hall or main living area and these rooms with doors.

Step 3


  Debris and dust from construction can lodge in HVAC units and the ductwork. This can affect indoor air quality, and possibly trigger allergic reactions in people living in the home. It can also reduce the effectiveness of the blower fan and heating and cooling elements. As soon as new ducts are installed, completely seal off each duct register and the HVAC unit to block out any construction dust. Use sealing methods and materials that will stay in place for the duration of the remodeling work. After construction is completely finished, vacuum the blower unit and ductwork as necessary.

Learn more about effective ductwork and heating & cooling.

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Source: Build It Green

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