Zone Control Dampers

Zone dampers let one forced-air system heat and cool different parts of a building to different temperatures. Hoyme builds motorized zone dampers in Camrose, Alberta, in 24 Vac and 120 Vac, with the heat bypass blade that single-speed furnaces need.

Single-speed furnace? Use the HAC-H

When every supply zone but one closes on a single-speed furnace, the furnace tries to push its full air volume through one open branch. Static pressure climbs, airflow across the heat exchanger drops, and the high limit trips. The HAC-H has a 10% heat bypass machined into the blade, so a closed zone still passes a minimum airflow and the plenum stays in range.

Put it on every supply zone damper on a single-speed system. Mixing bypass and non-bypass dampers makes the system behave differently depending on which zones happen to be closed. Variable speed and two-stage furnaces throttle back on their own and generally do not need the bypass. For return air zoning, the standard HAC with full shutoff is usually fine.

Pick the damper by branch size

• 2 to 9 in.: the HAC-H on the Hoyme spring motor drive, 24 Vac. Use the HAC-12H where only 120 Vac is available. Both are CSA certified.
• 6 to 14 in.: the HAC-50/51 quarter-turn, available with the -H bypass blade, in 6, 8, 9, 10, 12 and 14 in. Not CSA certified.
• BAS or proportional control: Belimo actuator dampers, on/off, 2 to 10 VDC modulating or floating point, 6 to 20 in.

Measure every branch before you order. Zone branches are rarely all the same size, and the largest branch decides which actuator family the system uses.

Options that matter on a zone job

• Action: power open or power close depends on how the zone panel drives the dampers. Check the panel documentation, then order every damper the same way.
• Relay: the HAC-51 has a relay on every unit, and on the HAC-50 it is optional. If the panel needs a relay output from every damper, order HAC-51 across the board.
• End switch: only where something downstream proves blade position.
• Pressure relief: the HAC-BPD back pressure damper relieves static pressure automatically when zones close, with no power or wiring.
• Transformer: each 24 Vac Hoyme spring motor damper draws 6 W at 0.32 A. Size the transformer for every damper on the circuit.

Example: four supply zones on a single-speed furnace

Branches of 10, 8, 6 and 6 in., a relay output from each damper, and power open per the zone panel: HAC-1051-OPO-H, HAC-0851-OPO-H and two HAC-0651-OPO-H. The 10 in. branch sets the actuator family, so the whole system stays on one actuator.

More detail: how to spec a zone control damper system and why high limits trip on single-speed zone systems.

Send the branch sizes and furnace type to technical support at 1-800-661-7382 and we will build the part numbers with you. Hoyme zone dampers are sold through HVAC wholesalers across Canada, or order direct here.