HAC-F Motorized Flue Damper, CSA Certified, Power Close / Spring Open, 4"–9", Relay and End Switch Included

A standard HAC uses Power Open / Spring Close action. It springs closed on power loss. On a flue application, if power is interrupted while the appliance is firing, the spring seals the flue. Combustion gases including carbon monoxide have nowhere to go. On a gas or oil appliance that creates CO accumulation in the appliance casing and back-draft risk into the building.

The HAC-F uses Power Close / Spring Open (SPC-F) action specifically because this is the code-correct fail-safe for a flue damper: the flue path is always clear on any power interruption. Do not substitute a standard HAC on a flue application regardless of size or voltage match.

It seems counterintuitive until you understand the fail-safe logic. The HAC-F is spring-open when there is no power: the flue is always clear when the damper is at rest. The end switch confirms this open position before the appliance is allowed to fire.

Once the end switch closes and completes the circuit to W, the appliance fires with the HAC-F spring-open: combustion gases vent freely through the open flue. After the heating cycle ends, power is restored to the HAC-F and the damper closes again, sealing the flue in standby and reducing heat loss between firing cycles.

If power is lost at any point (before, during, or after firing) the spring holds the damper open and the flue stays clear. The fail-safe is always toward an open flue. Power holds the damper closed between calls. The spring is what matters.

Yes, always. This is a safety requirement, not a recommendation. The appliance must not fire until the HAC-F end switch confirms the damper is in the spring-open (flue clear) position.

Without interlock, the appliance fires regardless of damper position, which means if the damper fails to open (motor fault, ice load, mechanical obstruction), the appliance fires into a partially or fully obstructed flue. That is the unsafe installation. With the HAC-F wired into the safety circuit as instructed, the appliance cannot fire unless the end switch confirms the flue is clear.

Operating a motorized flue damper without appliance interlock is a safety risk and a code violation on permitted installations in most Canadian and US jurisdictions. On 24 Vac, wire the HAC-F directly into the thermostat circuit as its installation instructions show. For millivolt or 120 Vac safety controls, see the ADP series page for model selection.

With the interlock wired correctly, the appliance cannot fire. The HAC-F end switch is in series with the thermostat wire, so the safety circuit stays open until the damper is in the spring-open (flue clear) position. If the damper fails to reach the open position (motor fault, mechanical obstruction, ice load) the end switch does not close and the appliance does not fire.

This is the correct fail-safe behaviour. The system fails safe: the appliance stays off rather than firing into an obstructed flue. This is why interlock is required on every HAC-F installation and why the end switch and relay are included on every unit.

Only if the safety circuit is not 24 Vac:

See the ADP series page for full model lineup and wiring diagrams.

The HAC-F is CSA certified. The HAC-FS uses the same damper body and actuator without CSA certification. It is for non-permitted applications where the AHJ genuinely does not require certification on the flue damper component.

On any permitted residential or commercial installation in Canada or the US where the AHJ will verify equipment, only the HAC-F satisfies the requirement. The difference between a certified and non-certified flue damper is a documented product qualification: an AHJ can and will verify it.

Order the HAC-F Large Diameter series, Belimo TFB24 actuator, available in even-inch sizes from 10" through 30". Same Power Close / Spring Open fail-safe. Relay and end switch included on every unit.

The standard HAC-F (4"–9") uses the stall-protected Hoyme SPC-F drive: the Hoyme drive is not rated for the torque required at 10" and above. The Belimo TFB24 is specified from 10" upward because it delivers the torque larger blade areas demand.

No: the relay and end switch are included on every HAC-F because a motorized flue damper installed without appliance interlock capability is an incomplete and unsafe installation. The end switch confirms the flue is clear before firing. The relay switches the damper motor with the call for heat. Both are required for a complete interlock.

Rather than create configurations where a contractor could inadvertently order a flue damper without interlock capability, both components are included on every unit regardless of size. There is no version of the HAC-F without relay and end switch: the complete interlock-ready assembly is the product.

No. The HAC-F is designed for fuel-burning appliance flue and vent runs, not dryer exhaust. The dryer exhaust environment (elevated temperature, lint, high humidity) is outside the HAC-F's listed application. Lint accumulation in the motor assembly causes premature failure.

For gas dryer exhaust applications requiring back draft protection, use a BDH Back Draft Hood at the wall termination: designed for the dryer exhaust environment. For gas dryer interlock requirements, see the ADP series for the correct relay adaptor for your application.

Yes: the Belimo TFB24 is available through Belimo distributors. The actuator mounts to the HAC-F damper body and can be replaced in the field without replacing the full damper assembly. Confirm the replacement actuator model matches the installed unit before ordering.

For the 4"–9" series, replacement Hoyme motor kits, microswitch kits, and spring return kits are available through Hoyme wholesalers, the same service parts as the HAC and HOM lineup.

Call Hoyme technical support directly. Have your flue pipe diameter, appliance type, system voltage, and whether the job is permitted ready, and we'll confirm the right HAC-F size and series, and whether you need an ADP, before you order.