Ductwork, Air Distribution, Ventilation, and Exhaust Systems for Houses
Ductwork and air distribution determine whether the equipment can actually deliver comfort. Ducts must be sized for the calculated airflow, supported, sealed, and insulated where required. Return air must come from acceptable spaces-not from bathrooms, garages, or spaces with contaminants-and transfer air paths must be provided where room doors are tight. Flexible duct is easy to misuse: sharp bends, excess length, and compression reduce airflow. Duct leakage into attics or crawl spaces wastes energy and can create pressure imbalances.
Ventilation and exhaust are separate from space heating. Houses need whole-house ventilation and local exhaust for kitchens and bathrooms. Exhaust fans must discharge outdoors, not into the attic or crawl space. Dryer vents must be short, smooth, and properly terminated. An HRV or ERV must be balanced and its ducts insulated where they pass through cold spaces. Make-up air is needed when large exhaust devices can depressurize the house and affect combustion appliances.
Traps: exhausting a bathroom fan into the attic; using a building cavity as a return plenum without proper construction and sealing; neglecting duct insulation in unconditioned space; and sizing ducts by guesswork. Another trap is to install a powerful kitchen exhaust without considering replacement air.
Worked example: a 6-inch round duct at a low static pressure may carry roughly 100 cfm, but that is only a sanity check. Use the actual airflow requirement and a duct-sizing table or calculator. If a bedroom needs 100 cfm and the drawing shows a long, flexible 5-inch duct with three elbows, expect a shortage; increase size or shorten the run, and verify with a pressure test or airflow measurement.