Zone jobs go wrong at the order desk, not in the mechanical room.
Somebody prices six identical dampers because it is all one system, then gets to site and two of the branches are 10 inch. Or they order a standard HAC for a 12 inch trunk and find out the drive is not rated for that blade. Or the whole thing goes in clean, runs fine for a month, and then the high limit starts tripping because nobody put the bypass blade on a single speed furnace.
Every one of those is fixable before anything ships.
Measure the Branches
Sounds obvious. It is still the most common way a zone order goes sideways.
The damper sits in the branch that feeds the zone, so branch diameter is the number that matters. And on most two storey houses those branches are not all the same. A main floor zone covering an open living area might be 10 inch while a back bedroom is on 6.
Walk it and write down every one before anybody quotes anything.
Bigger Duct, Different Actuator
Here is the part that catches people. The bigger the blade, the more torque it takes to move it against duct pressure. One actuator does not cover the whole range, so the size of the duct decides which product you are on.
| Size | Actuator | Product |
|---|---|---|
| 2" to 9" | Hoyme spring motor drive | HAC standard |
| 6" to 14" | Quarter turn, ¼" drive | HAC-50 / HAC-51 |
| 6" to 20" | Belimo TFB24, on/off | HAC-40 |
| 6" to 20" | Belimo modulating, 2 to 10 VDC | HAC-43 |
| 6" to 20" | Belimo floating point, 3 wire | HAC-34 / HAC-30 |
Few things worth pulling out of that table.
The Hoyme drive stops at 9 inch. That is a rating, not a suggestion. Past 9 you are on the quarter turn or a Belimo.
Between 6 and 9 you can go either way. Standard HAC or HAC-50/51, both CSA certified, same spring return, same options. The standard HAC is what most people use in that window. Once you are over 9 the choice makes itself.
No 7 inch in the HAC-50/51. That series runs 6, 8, 9, 10, 12 and 14. For a 7 inch branch use the standard HAC, which covers it fine. If you specifically want a quarter turn in 7 inch, that is a phone call to your wholesaler.
Modulating and floating point are there if the panel needs them. Most residential zone panels just want open or closed and the standard actuators do that. If you are on proportional control or DDC, the Belimo variants exist.
One more thing on the quarter turn. It sits on a ¼ inch drive shaft, which is the standard interface for quarter turn HVAC actuators. If one ever needs replacing you are not stuck with one proprietary part.
Single Speed Furnace? Every Supply Zone Needs the Bypass
This is the one that does not bite right away. It shows up a month later as a no heat call.
A single speed furnace moves one volume of air. Shut every supply zone but one and it is trying to push all of that through whatever is left open. Static pressure climbs, airflow across the heat exchanger drops, high limit trips to save it.
What stops it is the -H suffix. Ten percent bypass machined right into the blade, so a closed damper still leaves a path no matter what the control signal says. Every zone keeps bleeding a little and the plenum stays where it should be.
Available on every size in both the standard HAC and the HAC-50/51, and it is machined at the factory. Not something you add later.
Two rules:
- Single speed furnace means every supply zone damper gets it. Mix bypass and non bypass on one system and the thing behaves differently depending on which zones happen to be shut.
- Variable speed or two stage, you generally do not need it. The furnace throttles back to match.
Return air zoning is its own thing and full shutoff is usually fine there. More on all of this in the single speed zone control post.
Action
PO opens on power and springs shut when power drops. PC closes on power and springs open.
Which one you want on a zone system depends entirely on how the panel drives them. Some panels hold everything open and close the zones that are not calling. Others work the other way around. Check the panel documentation.
Just settle it before you order. The two look identical from outside and you will not know what you have until it is wired and powered up. On a zone job you are not fixing one damper, you are fixing all of them.
HAC-50 or HAC-51
Same damper. Same body, same actuator, same sizes, same options. The relay is the only difference.
HAC-51 has it standard on every unit. HAC-50 it is optional.
That matters more on a zone job than anywhere else. Eight dampers that all need a relay output, order HAC-51 and you just pick size, action and end switch and the relay is there every time. Order HAC-50 and you are adding the relay to eight separate lines, and sooner or later one gets missed.
HAC-51 when the relay is on everything. HAC-50 when it is the odd one out.
End Switch
S has one, O does not.
You need it when something downstream is waiting to hear the blade actually moved. A controller proving position, or an ADP relay adaptor running furnace fan sequencing.
Panel just opening and closing dampers with nothing waiting on confirmation, skip it.
Working Through a Four Zone Job
Two storey, single speed furnace, four supply zones. Branches come out at 10, 8, 6 and 6. Panel wants a relay off each damper.
So:
- Single speed, so -H on all four
- Relay on everything, so HAC-51 across the board
- The 10 inch is past the Hoyme drive anyway, so quarter turn is forced
- Action off the panel documentation, call it PO here
- Nothing proving position, so no end switch
Which gets you:
- HAC-1051-OPO-H, the 10 inch
- HAC-0851-OPO-H, the 8 inch
- HAC-0651-OPO-H, both 6 inch branches
One family, one actuator, one action, one suffix. Four lines and nothing for the counter to second guess.
If every branch had been 9 inch or under you could have run the standard HAC instead. Reason to stay on the quarter turn here is that the 10 inch forces it, and keeping one actuator across the system makes the wiring and the spares simpler.
Reading the Numbers
Same pattern as the rest of the line.
- HAC, then two digits for size. 06 is six inch, 10 is ten, 14 is fourteen.
- Drive code. 10 or 11 for the Hoyme drive, 50 or 51 for quarter turn, 40 and up for Belimo.
- O or S for end switch.
- PO or PC for action.
- Suffix if you need one. -H for bypass, -L for insulated.
HAC-1251-SPO is a 12 inch quarter turn with relay, end switch, power open. HAC-0850-OPC-L is an 8 inch quarter turn, no relay, power close, no end switch, insulated body. Full breakdown in the part number guide.
Before You Order
- Every branch measured, not guessed off the trunk
- Actuator picked off the biggest size in the system
- Furnace type confirmed, because that decides the -H
- Action checked against the zone panel documentation
- Relay sorted, HAC-51 if it is on everything
- End switch only where something is proving position
- -L on anything sitting somewhere condensation is a risk
All of it is CSA certified for Canada and the US, two year electrical and ten year mechanical.
If you have got the system but not the part numbers, call 1-800-661-7382 with the branch sizes and the furnace type. Five minute conversation, and cheaper than a second order.
View the HAC Inline Air Control Damper
Hoyme Manufacturing is a CSA-certified manufacturer of motorized dampers and airflow controls based in Camrose, Alberta. Products are available through HVAC wholesalers across Canada.