Most motorized dampers run on 24 Vac, and on a lot of jobs that is no problem at all. The furnace is right there, it has a 24 Vac control circuit, and the damper wires in alongside the thermostat.
Then there are the other jobs. The damper is going in a long way from the furnace. Or the thing it needs to follow is a 120 Vac exhaust fan, a range hood or a timer, not a thermostat. Or there is no furnace at all, just a boiler, a heat pump air handler or nothing with an accessible 24 Vac circuit. On those jobs, the question is how to get the damper the power and the signal it needs without making a mess of it.
There are three ways to do it with Hoyme parts. Here is when each one makes sense.
Option 1: the HAC-12, a damper that runs on 120 Vac
The HAC-12 is an HAC with a 24 Vac motor and a transformer built into the damper, so it connects straight to a 120 Vac supply. No separate transformer, no extra box on the wall.
- 4" to 9" diameter
- Spring return, power open (PO) or power close (PC)
- End switch available
- Canada/USA CSA certified
It also comes in two variations. The HAC-12L has a factory-insulated body for cold or unconditioned spaces, where condensation on the damper is a concern. The HAC-12H has the 10% heat bypass blade for hot air zone control, and it is not for fresh air or make-up air ducts.
Reach for the HAC-12 when 120 Vac is what you have at the damper and all you need the damper to do is open and close with that circuit.
Option 2: a standard HAC with an ADP relay adaptor
If the damper has to follow a 120 Vac device, like a bathroom exhaust fan or a range hood, the ADP-1101-05A is often the better tool. It is driven by the 120 Vac fan circuit and switches a standard 24 Vac HAC, so the damper opens when the fan runs and closes and seals when it stops.
The reason to choose this route over an HAC-12 is what else the adaptor can do. The ADP-1101-05A can also bring on the furnace fan with the exhaust fan, so the incoming air gets mixed through the house instead of pooling by the inlet. The HAC-12 on its own just opens and closes. Our ADP-1101-05A guide covers the sequence in detail.
The ADP route does need 24 Vac for the damper. On most furnace jobs that comes from the furnace transformer.
Option 3: a standard HAC with a separate transformer
You can always power a standard 24 Vac HAC from its own transformer, such as the Hoyme TRN-0024 (20 VA). It works, but at list it is the most expensive of the three, and it is one more box to mount and wire. In practice it makes the most sense when you need 24 Vac at the location for other controls as well.
What each option costs at list
For a 6" damper in power open, at 2026 suggested list:
- HAC-12 (HAC-0612-OPO): $246
- HAC plus ADP-1101-05A: $195 plus $88, so $283
- HAC plus TRN-0024 transformer: $195 plus $157, so $352
Your wholesaler's pricing will be different, but the order usually holds. The HAC-12 is the simplest and least expensive way to put a damper on 120 Vac. The ADP costs a bit more and does more.
A note on the furnace transformer
If you are taking 24 Vac from the furnace, the HAC's own load is small. The single motor is rated at 5 watts, and the relay coil, if fitted, draws 0.05 amps. Even so, check the transformer's capacity before you add anything to it, especially if it is already running a humidifier, zone controls or other accessories.
Things to get right
Pick PO or PC before you order. Both are set at the factory. Power open seals the duct whenever the circuit is off, which is the usual choice for fresh air. For make-up air, where you want the damper to spring open if power is lost, power close is the configuration we recommend. Our power open vs power close guide goes through it.
Line voltage wiring follows the electrical code. The HAC-12 connects to 120 Vac, so wire it to the diagram supplied with the damper and to the electrical code in force where you work.
Confirm unusual sequences first. If the damper has to interlock with an appliance, prove open before something starts, or follow more than one device, call technical support before you order. There is usually an ADP built for the job.
The short version
- 120 Vac at the damper and a simple open/close job: HAC-12.
- Damper should follow a 120 Vac fan or hood, maybe with the furnace fan too: HAC plus ADP-1101-05A.
- Need 24 Vac at the location for other controls anyway: HAC plus a TRN-0024 transformer.
- Cold or unconditioned space: HAC-12L. Hot air zone control: HAC-12H.
Hoyme dampers ship across Canada and the United States, and contractors can order through their HVAC wholesaler. Find a wholesaler near you. Not sure which option fits the job? Call free technical support at 1-800-661-7382 with the duct size, the supply voltage at the damper and what the damper needs to follow, and we will help you choose.