Make-Up Air Dampers

When an exhaust fan, range hood or gas dryer pushes air out of a tight house, the same amount of air has to come back in. Without a planned path it comes down the water heater flue or the furnace vent. A make-up air damper gives that air a dedicated duct, opens when the exhaust runs and seals the duct the rest of the time.

Three common jobs

• Range hoods over 400 CFM: the IRC requires make-up air for kitchen exhaust above 400 CFM. Read what the IRC requires and how to wire the damper.
• Ontario homes under OBC 2024: see make-up air under OBC Section 9.32.
• Gas dryers: see how to interlock a damper so the dryer only runs when it is open.

Pick the damper

• Inline, 24 Vac: the HAC, power open, 2 to 9 in. CSA certified. Use the HAC-12 where only 120 Vac is available at the damper.
• Damper in cold or unconditioned space: the insulated HAC-L or HAC-12L.
• No room for a straight run: the HAC-E motorized elbow damper.
• At the wall: the MAC terminating-end damper or the MOH motorized hood, which combine the damper and the exterior termination.
• Gas dryer air supply: the HOM, SF1 for a dryer-only duct or SF2 for a duct shared with the furnace.
• Inline damper with a passive hood: pair the HAC with an OOH all-weather inlet hood at the wall.

Pick the interlock

• Open the damper and start the furnace fan when the exhaust fan runs: the ADP-1101-05A from a 120 Vac exhaust fan switch. No end switch needed on the damper. See the ADP-1101-05A guide.
• The exhaust fan must wait until the damper proves open: a TPX proving adaptor (ADP-1102-TPX, ADP-1103-TPX, or RADP-1102-TPX for plug-in fans) with an end switch damper (SPO or SPC).
• Gas dryers: the RADP-0241-S10A, or the RADP-0242-S10A where the HAC on the return should also open when the furnace fires.
• Prove actual airflow, not just blade position: the PFS positive flow switch.

All of these are in the ADP relay adaptor range, with colour wiring diagrams in every box and in the Technical Library. Size the make-up air opening to the code in force; whether a given layout satisfies it is for the authority having jurisdiction to confirm.

Questions on sizing, voltage or wiring? Call technical support at 1-800-661-7382, free for contractors and installers. Sold through HVAC wholesalers across Canada, or order direct here.