HOM Motorized Combustion Air Damper, CSA Certified, 24 Vac, 4"–9", SF1 and SF2

Both SF1 and SF2 work identically: the damper opens by gravity when the appliance fires and power-closes when the appliance is idle. The only difference is how many appliances connect through the single damper.

It needs to interlock. A combustion air damper that stays open continuously provides no benefit over a passive hood: you've installed a motorized product and are operating it as a passive one. On systems where code requires controlled intake, continuous-open operation doesn't satisfy the requirement.

The correct installation has the HOM closed when the appliance is off and opening only when the appliance calls. The HOM's built-in end switch, wired in series with the thermostat wire, handles that interlock and holds the appliance off until the damper is open. On millivolt or 120 Vac controls, an ADP relay adaptor is added.

With the HOM wired into the safety circuit as instructed, the furnace cannot fire: the end switch holds the appliance off until the HOM is open.

Without interlock, the appliance fires regardless of damper position. On a cold morning with a frozen blade, that means combustion air is drawn from building infiltration, creating negative pressure, combustion quality problems and carbon monoxide risk.

Both SF1 and SF2 include the relay and end switch. The choice depends only on how many appliances connect through the damper:

On a 24 Vac appliance, the end switch is wired in series with the thermostat wire to W, so the appliance cannot fire until the damper has opened. No ADP is needed. On millivolt and 120 Vac safety controls, the ADP-0MV2-S5A or ADP-1102-S5A provides the same interlock.

No. Lint from dryer exhaust accumulates in the motor assembly and causes premature failure. The HOM is not rated or suitable for dryer ventilation.

Use the Hoyme BDH Back Draft Hood for dryer exhaust terminations. It is designed for that application.

Both achieve the same interlock function. The choice is usually driven by wall construction and installation access: whether it's easier to place the control point beside the appliance or at the exterior wall. See the MOH product page for details.

Yes. The HOM is rated for low-temperature air applications. The stall-protected Hoyme spring motor drive with nylon bearings is engineered for the freeze-thaw cycling and cold temperature exposure of a combustion air intake on a Canadian or northern U.S. installation.

The stall-protected Synchron motor holds against load without tripping, including when the blade is held against ice at startup. If the blade is frozen, the motor holds, the end switch signal is not received and the appliance stays off. The fault is detectable rather than invisible.

The HOM mounts inside the appliance area, on a bracket fastened to the side of the appliance or plenum. Mount the bracket vertically, with its bottom within one foot above burner level and within two feet horizontally of the front of the appliance, and secure the bottom of the expanded metal cage with a sheet metal screw. For a damper and hood combined at the exterior wall, see the MOH.

Call Hoyme technical support directly. Have your appliance type, BTU input, system voltage and duct size ready, and we'll confirm the right HOM variant, and whether you need an ADP, before you order.