CSA Certified · 24 Vac · 4"–9" · Spring Return

HOM Motorized
Combustion Air
Damper

Your furnace won't fire until this damper opens. That's the point.

✓ Appliance cannot fire until the damper proves open — interlock by design
✓ CSA certified complete assembly — Canadian and US installations
✓ Patented Hoyme spring motor drive — stall-protected Synchron motor, nylon bearings
✓ SF1 (one appliance) or SF2 (two appliances) — opens by gravity when appliance fires, power-closes when idle
✓ Available 4", 5", 6", 7", 8", 9" — end switch included on SF1 and SF2
✓ Adjustable extension sleeve 7½"–14" wall thickness · Flashing included
✓ Furnaces, boilers, fireplaces, water heaters — not suitable for dryer exhaust
CSA certified — complete assembly
Stall-protected Synchron motor — nylon bearings
2-yr electrical · 10-yr mechanical warranty
Flashing included — sleeve 7½" to 14"
Hoyme HOM Motorized Combustion Air Damper — CSA certified, 24 Vac, spring return, 4–9 inch
Is this the right product?
✔ Right product if
You need a CSA-certified motorized damper to control outside combustion air intake on a fuel-burning appliance — furnace, boiler, fireplace, or water heater — interlocked so the appliance cannot fire until the damper proves open.
✗ Not this product if
Dryer exhaust termination → use BDH Back Draft Hood. Lint in the motor assembly causes premature failure — the HOM is not rated for dryer exhaust.

Damper and hood combined at the exterior wall → use MOH Motorized Hood.

Fresh air ventilation control → use HAC Inline Damper.

What It Does

Combustion Air That Opens on Demand.
Seals When It Doesn't.

A constantly open combustion air duct is an energy loss every hour the appliance isn't running — and a code compliance problem on every job that requires controlled intake. The HOM closes that opening.

Hoyme HOM Motorized Combustion Air Damper — typical residential installation showing damper inline in combustion air duct run

How Combustion Air Interlock Works

When a combustion air damper is properly interlocked with a furnace or boiler, the appliance cannot fire until the damper proves open. The HOM opens when the ADP relay adaptor receives the call signal from the appliance safety circuit. Once the HOM reaches full open, the end switch — on SF1 and SF2 variants — closes and sends a confirmation signal back to the relay adaptor, which then allows the appliance to fire.

1
Appliance calls for heat
ADP relay adaptor receives the signal from the appliance safety circuit
2
HOM opens — end switch confirms
Damper blade physically reaches open position — end switch closes, sends proved-open signal to ADP
3
Appliance fires
ADP relay allows the appliance to fire — combustion air path is confirmed open
If the damper fails to open for any reason — frozen blade, motor fault, wiring problem — the appliance stays off and the fault is detectable. Without interlock, the appliance fires regardless of damper position and the fault is invisible.

Where It's Installed

Gas & Propane Furnaces
New construction and retrofit combustion air intake — the most common HOM application across Canada
Boilers — Residential & Light Commercial
Combustion air control interlocked with 110 Vac boiler control circuit via ADP-1102-S5A or ADP-1102-10A
Fireplaces & Inserts
Combustion air makeup at the building wall for gas fireplaces and fireplace inserts
Atmospherically-Vented Water Heaters
Combustion air on atmospherically-vented gas water heaters — millivolt systems use ADP-0MV2-S5A
Make-Up Air — Furnace Fan Interlock
Central ventilation system makeup air control interlocked with furnace fan — opens with appliance call, seals when appliance is off
NOT for Dryer Exhaust
Lint accumulation in the motor assembly causes premature failure. Use the BDH Back Draft Hood for dryer exhaust terminations.
What's in the Box
✓ HOM motorized combustion air damper assembly — configured as ordered
✓ Adjustable extension sleeve — 7½" to 14" wall thickness
✓ ¼" screen — installed for intake, remove for exhaust applications
✓ Flashing for siding or stucco installation
✓ Installation instructions
You supply: 24 Vac control wiring, ADP relay adaptor, duct connection hardware. Do not wire the HOM directly to the appliance thermostat — connect to ADP relay adaptor output only.
Required Companion Product
ADP Interface Relay Adaptor
The HOM must be interlocked with the appliance via an ADP relay adaptor. Select by appliance type and system voltage:
→ Gas furnace, millivolt — ADP-0MV2-S5A
→ Gas furnace, 24 Vac — ADP-0240-S5A
→ Boiler / tankless, 110 Vac — ADP-1102-S5A or ADP-1102-10A
View ADP Relay Adaptors →

Variant Selector

SF1 or SF2 — One Appliance or Two?

Both HOM variants work identically: the damper opens by gravity when the appliance calls and power-closes when the appliance is off. The only choice is how many appliances the single HOM unit controls.

Both Variants — Same Fixed Action
All standard HOM dampers are gravity/spring open. The appliance transformer powers the motor to close the damper when the appliance is idle. When the appliance calls for heat, power is interrupted to the motor — the damper drops open by gravity. This prevents overloading the appliance transformer during the firing cycle.
Appliance firing (no motor power)
Damper open — gravity
Appliance idle (motor powered)
Damper closed — power
Most Common
SF1 One Appliance
Appliances controlled
1
Part number (e.g. 6")
HOM-0611-SF1
Relay
Included
End switch
Included

The SF1 connects a single HOM damper to one appliance. The damper end switch proves position to the ADP relay adaptor, which holds the appliance off until the blade is confirmed open. One set of wiring terminals (1, 2, 3) connects to the single appliance safety circuit.

Use SF1 when:
✓ Only one appliance is interlocked to this damper
✓ Single furnace, single boiler, or single water heater
✓ Standard residential installation — most common application
SF2 Two Appliances
Appliances controlled
2
Part number (e.g. 6")
HOM-0612-SF2
Relay
Included
End switch
Included

The SF2 connects a single HOM damper to two appliances simultaneously — the damper must open before either appliance fires. It adds a second set of wiring terminals (6, 7, 8) for the second appliance circuit. The SF2 is installed nearest the largest appliance and in proximity to the secondary appliance.

Use SF2 when:
✓ Two appliances share the same combustion air duct
✓ Furnace and water heater on the same combustion air run
✓ Both appliances must be interlocked through one damper
✓ The damper opens when either appliance calls for heat
One Question — Which Variant Do You Need?
How many appliances connect to this combustion air duct?
One appliance — furnace, boiler, water heater, or fireplace — interlocked through this single damper
SF1 — One appliance
Two appliances share the same combustion air duct?
Both appliances are interlocked through one damper — the damper must open before either fires
SF2 — Two appliances
Variant Appliances Relay End Switch Primary Application
SF1 1 appliance Included Included

Single furnace, boiler, water heater, or fireplace. Most common.

SF2 2 appliances Included Included Two appliances sharing one combustion air duct — both interlocked through one damper
Choosing SF1 vs SF2 is separate from choosing your ADP model
The SF1/SF2 choice depends only on the number of appliances. Your ADP relay adaptor model depends on the appliance type and system voltage — not on whether you need SF1 or SF2. Both SF1 and SF2 connect to the same ADP series.
→ Gas furnace, millivolt — ADP-0MV2-S5A
→ Gas furnace, 24 Vac — ADP-0240-S5A
→ Boiler / tankless, 110 Vac — ADP-1102-S5A or ADP-1102-10A
Not sure whether you need SF1 or SF2?
Count the appliances connected to the combustion air duct. One appliance → SF1. Two appliances through one damper → SF2. Call technical support if you're uncertain.

CONFIGURATION GUIDE

Order the Right HOM the First Time

Three decisions determine your part number. All options are factory-set — none are field-adjustable after installation. Confirm before ordering.

1

Select size — match to combustion air duct diameter

Available in 4", 5", 6", 7", 8", and 9". Match the HOM to the combustion air duct diameter — not the appliance inlet collar. Use the sizing table on the Code Compliance page to confirm required opening area based on total appliance BTU input.

4"

Up to 100K BTU

5"

Most common

6"

Most common

7"

Multiple appliances

8"

Multiple appliances

9"

Light commercial

2

Select variant — SF1 (one appliance) or SF2 (two appliances)

Both variants include relay and end switch. The end switch proves the blade is fully open to the ADP relay adaptor before the appliance fires. The only difference is how many appliance circuits connect through the single damper.

SF1 MOST COMMON

Relay included · end switch included
Connects to one appliance

SF2

Relay included · end switch included
Connects to two appliances simultaneously — damper must open before either fires

3

Select ADP relay adaptor — by appliance type and system voltage

Do not wire the HOM directly to the appliance thermostat or safety circuit. Connect to the ADP relay adaptor output — the ADP manages the interlock sequence and holds the appliance off until the end switch confirms the HOM is fully open.

ADP-0MV2-S5A

Gas furnace — millivolt / standing pilot / thermopile safety system

ADP-0240-S5A

Gas furnace — 24 Vac electronic ignition · most common

ADP-1102-S5A

Boiler or tankless water heater — 110 Vac · up to 5A load

ADP-1102-10A

Boiler or tankless water heater — 110 Vac · up to 10A load · confirm appliance spec label

View Full ADP Series →

HOW TO READ YOUR PART NUMBER

HOM

Product

–
06

Size (6")

11

Variant code

–
SF1

1 appliance

SIZE CODES

04=4" · 05=5" · 06=6" · 07=7" · 08=8" · 09=9"

VARIANT CODE

11 = SF1 (one appliance) · 12 = SF2 (two appliances)

INCLUDED ON BOTH

Relay · end switch · adjustable sleeve · flashing

ONE APPLIANCE — MOST COMMON

HOM-0611-SF1

6" · one appliance · relay · end switch

TWO APPLIANCES

HOM-0612-SF2

6" · two appliances · relay · end switch

LARGER DUCT — ONE APPLIANCE

HOM-0811-SF1

8" · one appliance · relay · end switch

Why Hoyme

Built for a Combustion Air Intake — Not Adapted for One

Most motorized dampers use a commodity actuator mounted to a stamped-metal body. The HOM is built around Hoyme's patented spring motor drive — engineered specifically for the mechanical demands of a combustion air intake in a Canadian or northern U.S. climate.

The Patented Hoyme Spring Motor Drive

A 24 Vac, 5-watt Synchron motor with nylon bearing assembly — engineered together as a single integrated drive, not a commodity actuator attached after the fact. That matters on a combustion air intake that sees twenty years of freeze-thaw cycling, outdoor temperature exposure, and stall loads when the blade is held against ice or elevated static pressure.

Stall-protected — not circuit-protected
A circuit-protected motor trips on stall and leaves the blade in an unknown position. On a combustion air safety application that is an invisible fault. The Hoyme drive holds against load without tripping — if the blade is held against ice, the fault is detectable via the end switch signal.
Nylon bearing assembly
Engineered for freeze-thaw cycling and the cold temperature exposure of a combustion air intake on a Canadian or northern U.S. installation — not a warm mechanical room application.
Serviceable in place
Motor kits, microswitch kits, and spring return kits are stocked at Hoyme wholesalers. A motor failure does not require full damper replacement — the drive services in place. Commodity actuators typically require complete unit replacement.
CSA certified — complete assembly
CSA certification covers the HOM damper body, the drive, and the control hardware together — not just the motor. The adjustable extension sleeve accommodates wall thicknesses from 7½" to 14" without custom fabrication. Flashing is included.
Hoyme HOM Motorized Combustion Air Dampers — commercial installation showing multiple units on a shared combustion air plenum
Commercial installation — multiple HOM units serving a shared combustion air plenum. Each damper interlocked independently to its appliance via ADP relay adaptor.

CSA Certified. End Switch Confirmed. Inspection Ready.

CSA certified — Canadian and U.S. installations
Complete assembly certification — body, drive, and control hardware together
End switch confirms physical blade position
SF1 and SF2 variants — proves damper is open before appliance fires, not just that power was applied
2-year electrical · 10-year mechanical warranty
Parts stocked at Hoyme wholesalers — serviceable in place
Adjustable extension sleeve — 7½" to 14"
Accommodates wall thickness variation without custom fabrication. Flashing included.
Rated for low-temperature air
Engineered for Canadian and northern U.S. climate installations — not a warm mechanical room product

Key Specs at a Glance

Voltage
24 Vac · 5W
Sizes
4", 5", 6", 7", 8", 9"
Motor
Synchron — stall-protected
Certification
CSA — complete assembly
Wall Thickness
7½" to 14" adjustable
Warranty
2-yr elec · 10-yr mech
Included
Flashing · screen · sleeve
Not Suitable For
Dryer exhaust — use BDH
Hoyme HOM vs. Generic Motorized Damper on a Combustion Air Application
Generic Motorized Damper
Commodity actuator — circuit-protected, trips on stall, leaves blade position unknown
Motor failure requires full unit replacement — no serviceable parts
Actuator certified — damper body typically not. Inspection documentation incomplete.
Not engineered for freeze-thaw cycling on a combustion air intake
Wall sleeve and flashing sourced separately — extra time on every install
Hoyme HOM
Patented integrated drive — stall-protected Synchron motor, holds under load without tripping
Motor kits serviceable in place — stocked at Hoyme wholesalers
CSA certified — complete assembly, body and drive together. Inspection ready.
Nylon bearings engineered for freeze-thaw cycling on combustion air intake
Adjustable sleeve 7½"–14" and flashing included — complete install kit

Shop HOM Dampers

Order Your HOM

SF1 is the correct variant for most combustion air applications — one appliance interlocked through one damper. If unsure, confirm your variant and size before ordering — both are factory-set and cannot be changed after installation.

Hoyme HOM Motorized Combustion Air Damper
CSA Certified
HOM Motorized Combustion Air Damper
24 Vac  ·  4"–9"  ·  Spring return  ·  SF1 (one appliance) or SF2 (two appliances)  ·  Furnaces, boilers, fireplaces, water heaters
Shop HOM →

Variant Quick Reference

SF1 Most Common
One appliance
Relay + end switch included · connects to one appliance safety circuit · required for ADP combustion air interlock
SF2
Two appliances
Relay + end switch included · connects to two appliance safety circuits simultaneously · damper must open before either appliance fires

Required Companion — Order with HOM

ADP-0MV2-S5A Millivolt Relay Adaptor
Gas furnace · millivolt / standing pilot
ADP-0MV2-S5A
Only model rated for millivolt safety circuits · order HOM SF1
ADP-0240-S5A 24 Vac Relay Adaptor
Gas furnace · 24 Vac
ADP-0240-S5A
Most common combustion air interlock · order HOM SF1
ADP-1102-10A 110 Vac Relay Adaptor
Boiler / tankless · 110 Vac
ADP-1102-S5A or ADP-1102-10A
Confirm load rating on appliance spec label · order HOM SF1
Not sure which variant or size is right for your job?
Call technical support with your appliance type, BTU input, system voltage, and duct size — we'll confirm the right HOM and ADP before you order.

COMMON QUESTIONS

HOM Combustion Air Damper FAQs

Questions contractors and counter staff ask most often — answered directly from the product.

What's the difference between SF1 and SF2 — which one do I need for a furnace combustion air intake? +

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.

SF1 — one appliance

One furnace, boiler, water heater, or fireplace connected through this damper. The most common specification for residential combustion air. Relay and end switch included.

SF2 — two appliances

Two appliances share the same combustion air duct — the damper must open before either fires. Adds a second set of wiring terminals for the second appliance circuit. Relay and end switch included.

For most residential combustion air applications with one furnace or boiler, SF1 is correct. Count the appliances connected to the combustion air duct before ordering.

Does the HOM need to be interlocked with the furnace — or can I wire it to stay open continuously? +

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 ADP relay adaptor handles that interlock, including holding the appliance off until the HOM end switch confirms the damper is fully open.

What happens if the damper doesn't open and the furnace tries to fire? +

With proper ADP interlock and the SF1 end switch variant, the furnace cannot fire — the relay circuit holds the appliance off until the end switch confirms the HOM is fully open.

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

The interlock is the protection, and the end switch is what makes the interlock reliable. That is why the SF1 variant — which includes both relay and end switch — is required for ADP combustion air interlock applications.

Which variant do I need if I'm using an ADP relay adaptor for combustion air interlock? +

Both SF1 and SF2 include relay and end switch — either will work with ADP interlock. The choice depends only on how many appliances connect through the damper:

SF1 — one appliance

One furnace, boiler, water heater, or fireplace interlocked through this damper. Used with ADP-0MV2-S5A, ADP-0240-S5A, and ADP-1102 series. The most common specification.

SF2 — two appliances

Two appliances share one combustion air duct — both connected to the same damper. The damper must open before either appliance fires. Each appliance connects to its own set of wiring terminals.

The ADP relay adaptor uses the end switch signal to confirm the damper has physically reached the open position before allowing the appliance to fire. Without the end switch, the ADP has no position confirmation signal and the interlock sequence cannot function correctly.

Can I use the HOM for dryer exhaust? +

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 specifically designed for that application.

What's the difference between the HOM and the MOH? +

HOM — inline damper

Installs inline in the duct run — the exterior termination is handled by a separate hood (OOH or existing opening). Use when the control point belongs in the duct run rather than at the wall.

MOH — motorized all-weather hood

Replaces the exterior hood fitting and provides damper control at the wall penetration in one combined unit. Use when combining the hood and damper at the exterior wall is preferred.

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 inside the duct run or at the exterior wall. See the MOH product page for details.

Is the HOM suitable for low-temperature combustion air applications? +

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

What wall thickness does the HOM accommodate? Is flashing included? +

The adjustable extension sleeve included with the HOM accommodates wall thicknesses from 7½" to 14" without custom fabrication. Flashing for siding or stucco installation is included in every box.

If the wall is unusually thick or thin — outside the 7½"–14" range — measure before ordering and call technical support to confirm. Confirm flashing compatibility with exterior cladding type before cutting the wall opening.

Who do I call if I'm unsure which variant or ADP model to order? +

Call Hoyme technical support directly. Have your appliance type, BTU input, system voltage, duct size, and wall thickness ready — the call is typically under five minutes and we'll confirm the right HOM variant and ADP model before you order.

READY TO ORDER

The Right HOM. Right Variant. Right ADP. First Time.

Shop the HOM directly, or call technical support with your appliance type, BTU input, system voltage, and duct size — we'll confirm the right variant and ADP model before you order.

✓ CSA certified — complete assembly
✓ Patented spring drive — stall-protected Synchron motor
✓ 2-yr electrical · 10-yr mechanical warranty
✓ Adjustable sleeve 7½"–14" · flashing included
✓ In stock at Canadian HVAC wholesalers