The HAC
Universal Inline
Air Control Damper

PO (Power Open) — the damper opens when 24 Vac is applied and spring-closes when power is removed. PC (Power Close) — the damper closes when powered and spring-opens on power loss.

For fresh air intake, make-up air, and HRV/ERV applications, PO is correct for most installations. You want the duct sealed when the ventilation system is not calling — that's the spring-closed (power off) position. PO delivers that.

PC is specified when the system design requires the duct to remain open if power is lost — uncommon on fresh air intakes but appropriate on some exhaust and pressure control applications.

Three decisions determine your part number:

Then confirm whether the standard HAC is right or whether a variant applies — see the configuration guide above, or call technical support with your appliance type, BTU input, duct size, and location.

They do different things and both can be ordered on the same unit.

If you're unsure which option your system needs, call technical support with the appliance type and control sequence — we'll confirm before you order.

Yes — HRV and ERV applications are one of the most common uses for the HAC. The HAC installs on the fresh air supply duct and is wired to the HRV or ERV ventilation output. It opens when the unit calls for a ventilation cycle and closes when the cycle ends.

This matters because a passive installation leaves the fresh air duct open through the HRV core when the unit is off — which is a real infiltration path. The HAC closes that path between cycles.

HRVs and ERVs manage ventilation air quality. The HAC manages the duct — they work together, not instead of each other. For fresh air installations also requiring furnace fan sequencing, pair with the ADP-0241-S5A — it opens the HAC first, confirms position, then energizes the furnace fan to prevent cold air discharge at the registers.

If your thermostat or controller outputs a direct 24 Vac signal to open the damper when ventilation is called, you can wire the HAC directly — no adaptor needed.

If you need the damper to sequence with a furnace fan — opening first, then allowing the fan to run — the ADP-0241-S5A is required. It manages the open/confirm/run sequence automatically and prevents the cold air dump that occurs when the fan and damper are wired in parallel.

For ventilation code compliance installations where the fresh air damper must prove open before the furnace fan runs, the ADP-0241-S5A is the correct solution. See the ADP series for the full model lineup including combustion air, gas dryer, and two-zone applications.

Many installs use both — a HAC on the fresh air ventilation duct and a HOM on the combustion air duct. They serve different code requirements. If you're controlling combustion air on a gas or oil appliance, you need the HOM, not the HAC.

Start with the most common causes before assuming a product fault:

Replacement parts — motor kits, microswitch kits, spring return kits — are stocked at Hoyme wholesalers and can be serviced in place. If the issue is not resolved with the above, call technical support at 1-800-661-7382.

Yes. The HAC installs inline in the round duct run at any accessible point — it does not require access to the appliance or exterior wall. The mounting collar is included; no separate collar is required for standard duct connections.

For retrofits where the damper location is in an unconditioned space, near the exterior wall, or in a crawlspace, consider the HAC-L with factory-insulated body to prevent condensation at the damper location.

The main planning consideration on retrofits is 24 Vac control wiring — plan the wire run from the controller or ADP location to the damper. If only 120 Vac is available at the damper location, see the HAC-12 with built-in transformer.

Call Hoyme technical support directly. Have your appliance type, BTU input, duct size, location (province or state), and control sequence ready — the call is typically under five minutes and we'll confirm the right product and part number before you order.