How to Connect Heat Ducts
- 1). Route heating ducts through a basement or insulated crawl space if possible, so they can be secured to floor joists. Use an attic as an alternative and run a main supply duct up from the unit to the attic through a closet or large wall cavity. A new house under construction can have framing easily modified to provide this space. Make as many straight runs as possible. Use flexible ducting called flexduct, formed of coiled wire, with fiberglass insulation and a metallic outer layer.
- 2). Start duct work at the supply plenum, a large sheet metal opening, on the unit. Secure the duct as recommended by the manufacturer, usually with sheet metal screws and/or heat-resistant tape. Fasten duct work to floor joists or wall studs with metal straps with go around the duct to secure it. Install the entire main supply duct first.
- 3). Cut openings in the flexduct for branches with tin snips. Connect smaller branch ducts with metal sleeve connectors, which fit inside the open ends of ducts and are sealed with heat-resistant tape on the seams. Use T-connectors for right-angle branches. Use Y-connectors where possible to pull two branches from the same main supply opening to reduce the number of seams and potential leaks.
- 4). Connect branch ducts to heating vents, along outside walls, and seal those seams with tape. Most vents have metal connectors that slip into the flexduct. Adapt the connection to the vent. Floor vents, wall vents and attic vents may use slightly different connectors. Under-floor duct work will usually connect to floor vents, and attic duct work may connect to either wall vents, through small ducts run down inside wall cavities or to ceiling vents.
- 5). Install a return system to collect "used" air and return it to the heating unit. Ideally place a return in every space with a vent; practically put large return openings in some central space like a hallway, fairly close to the unit. Size return vents to equal the total airflow capacity of the supply side. Place returns in walls where frames can be fastened to wall studs to hold filters to catch dust and dirt before the air returns to the unit.
- 6). Seal all joints and seams thoroughly with heat-resistant tape recommended by the duct manufacturers. Don't use duct tape, as its adhesive will not hold up in a heating system. Test the duct system by forcing the heating blower to turn on by adjusting the thermostat. Listen for whistling sounds that indicate air leaks and look for any blowing tape or duct work.