Efficient Ductwork Cuts Heating and Cooling Costs
Winners of the NAHB Research Center's EnergyValue Housing Award (EVHA) have found innovative ways to ensure the efficiency of ductwork, which is responsible for as much as one-fifth to even one-third of a home’s heating and cooling energy use.
The winning builders are saving home owners money and improving comfort by bringing ducts into conditioned space, sealing ducts against air leakage and creating efficient designs.
The best practices for creating energy-efficient duct systems include:
- Planning duct location and size during the architectural stage
- Using ACCA Manual J, D and S sizing calculations for the HVAC system
- Placing all ducts and mechanical equipment in conditioned space
- Sealing ducts and connections with mastic paste and/or UL-listed pressure tape, paying careful attention to sealing around the supply cabinet
- Making duct runs as short and straight as possible, and placing supply registers at the building interior in tightly-built, well-insulated homes
- Always using hard-ducted returns
- Using transfer grilles across interior doorways to equalize pressure if a ducted return is not possible
- Testing the duct system for air leakage before enclosing with drywall
Production builder Aspen Homes of Colorado simplifies bringing ductwork into conditioned space by using a conditioned crawlspace — or a “very short basement,” according to Rob Sabin, the company’s director of research and development.
The builder’s two-story designs, however, require foresight for efficient mechanical system planning. “We make sure the duct layout is planned at the same time as the framing and joists,” he said. “Because we do our own design, and because we build entry level homes [with simple rooflines and building shapes], it’s a little easier.”
A centrally-located furnace keeps duct runs short and, where possible, supply ducts have minimal curves and branching.
Sunterra Homes of Bend, Ore., often uses an unvented attic design, which brings ducts into conditioned space by moving the building insulation to the roofline. To manage the high cost of the polyurethane foam attic insulation, the builder combines 3 inches of foam with batt insulation.
The unconventional design, however, didn’t initially meet code approval, and the builder worked with the state energy office to finally obtain approval.
“It’s always a fight,” said Jim Chauncey, the company’s president. “You are at the whim of the building official.” And, he added, although his company always tries to place all of the ductwork in conditioned space, “It can’t always be accomplished. Sometimes you have to penetrate the building envelope because of design logistics.”
Chauncey estimated that the entire insulation system, including spray foam in the wall cavities, adds about $3,000 to a 2,000-square-foot single-family house, “a small price to pay for what it gives you,” he said.
Ferrier Builders of Ft. Worth, Texas uses Structural Insulated Panel (SIP) roofs on most of its homes to create an unvented roof. The vaulted ceilings created by the SIPs present a unique challenge for running ducts without compromising aesthetics. One solution the company has found is to keep the blower in a central area, such as a bathroom or closet with a flat ceiling, and then to use sidewall vents to supply air to the adjoining spaces.
Other locations for ductwork in conditioned space include:
- Open-webbed floor trusses (with the rim joist carefully sealed and insulated)
- Constructed bulkheads or soffits
- Dropped or flat ceilings
- Furred-down hallway plenums
Applications for the 2007 EnergyValue Housing Awards are now available.
For more information about the awards program or to apply, click here.
For more information about duct design, check out the PATH Technology Inventory or obtain a copy of “A Builder’s Guide to Placement of Ducts in Conditioned Space” from the NAHB Research Center.