CSA Certified · 24 Vac · 4"–9" · Seals at the Wall

MOH Motorized
All-Weather
Hood Damper

Motorized damper and all-weather hood in one unit — seals at the building wall, not in the duct run.

✓Hood and damper combined — one wall penetration, no separate hood or inline damper
✓Seals at the building exterior — no cold air column in the duct between cycles
✓Patented Hoyme spring motor drive — same stall-protected Synchron motor as HAC and HOM
✓CSA certified complete assembly — fresh air, combustion air, make-up air, HRV/ERV termination
✓PO or PC — end switch available for combustion air interlock
✓Adjustable extension sleeve 7½"–14" · flashing included · sizes 4"–9"
✓Not suitable for dryer exhaust — use BDH Back Draft Hood
CSA certified — complete assembly
Seals at the wall — no cold air column in the duct
Hood + damper + sleeve + flashing — one unit
2-yr electrical · 10-yr mechanical warranty
Hoyme MOH Motorized All-Weather Hood Damper — CSA certified, 24 Vac, seals at the wall
Is this the right product?
✔ Right product if
You need a motorized damper and an all-weather hood at the same wall penetration — fresh air intake, exhaust control, combustion air, or make-up air. One unit at the wall does both jobs.
✗ Not this product if
Damper needs to be in the duct run rather than at the wall → use HAC inline damper with OOH at exterior.

Inline combustion air damper → use HOM.

Dryer exhaust termination → use BDH Back Draft Hood — MOH is not rated for dryer exhaust.
CSA Certified · 24 Vac · 4"–8" · Seals at the Wall

MOH Motorized
All-Weather
Hood Damper

Motorized damper and all-weather hood in one unit — seals at the building wall, not in the duct run.

✓ Hood and damper combined — one wall penetration, no separate hood or inline damper
✓ Seals at the building exterior — no cold air column in the duct between cycles
✓ Patented Hoyme spring motor drive — same stall-protected Synchron motor as HAC and HOM
✓ CSA certified complete assembly — fresh air, combustion air, make-up air, HRV/ERV termination
✓ PO or PC — end switch available for combustion air interlock
✓ Adjustable extension sleeve 7½"–14" · flashing included · sizes 4"–8"
✓ Not suitable for dryer exhaust — use BDH Back Draft Hood
CSA certified — complete assembly
Seals at the wall — no cold air column in the duct
Hood + damper + sleeve + flashing — one unit
2-yr electrical · 10-yr mechanical warranty
Hoyme MOH Motorized All-Weather Hood Damper — CSA certified, 24 Vac, seals at the wall
Is this the right product?
✔ Right product if
You need a motorized damper and an all-weather hood at the same wall penetration — fresh air intake, exhaust control, combustion air, or make-up air. One unit at the wall does both jobs.
✗ Not this product if
Damper needs to be in the duct run rather than at the wall → use HAC inline damper with OOH at exterior.

Inline combustion air damper → use HOM.

Dryer exhaust termination → use BDH Back Draft Hood — MOH is not rated for dryer exhaust.

Which Installation Is Right?

MOH at the Wall — or HAC in the Duct?

Both achieve motorized damper control on an outdoor air penetration. The right choice depends on where the control point belongs — at the wall, or somewhere in the duct run.

Hoyme MOH Motorized All-Weather Hood Damper — seals at the wall
MOH Seals at the wall

Hood, damper, sleeve, and flashing in one unit. Mounts at the wall penetration. No duct run between the damper blade and outside air. The wall penetration is the control point.

✓ Wall penetration is the natural control point
✓ No separate hood already in place — new installation
✓ Eliminates cold air column between hood and inline damper
✓ One product, one installation point — simpler than two separate items
✓ CSA certified — combustion air on fuel-burning appliances
Hoyme HAC Inline Motorized Damper — seals in the duct run
HAC Seals in the duct run

Inline damper in the round duct at any accessible point inside the building. Separate exterior hood remains in place. Control point is wherever the HAC is installed — not necessarily at the wall.

✓ Existing hood already in place — add damper without changing exterior
✓ Control point needs to be away from the wall — interior mechanical room location
✓ Need insulated body (HAC-L) for cold climate duct run
✓ Need heat bypass blade (HAC-H) for hot air zone supply
✓ Available 2"–9" — wider size range than MOH
Condition Use MOH Use HAC

Wall penetration is the natural control point

✓ Yes
— Adds second location

Separate all-weather hood already in place

— Redundant
✓ Add HAC inline

Need insulated damper body — cold climate duct run

— Seals at wall
✓ Use HAC-L

Need heat bypass blade — hot air supply zone control

— Not available on MOH
✓ Use HAC-H

Need relay output for control sequences

— Not available
✓ With relay option

Retrofit — existing hood in place

— Replaces existing hood
✓ Add inline, keep hood

CSA certified combustion air interlock

✓ With end switch + ADP
— Use HOM for inline

Size range needed beyond 8"

MOH max is 8"
✓ HAC-50/51 up to 12"
Still not sure which is right for your job?
Call technical support with your application, wall construction, and whether a hood is already in place — the call is typically under five minutes.

CONFIGURATION GUIDE

Order the Right MOH the First Time

Three decisions determine your part number. Action and end switch are factory-set — confirm before ordering.

1

Select size — match to your round duct diameter

Available in 4", 5", 6", 7", and 8". Match the MOH to the duct diameter — not the appliance inlet collar. If the wall thickness is non-standard, measure the 'L' dimension before ordering — the adjustable sleeve covers 7½" to 14".

4"

Small intake

5"

Most common

6"

Most common

7"

Full options

8"

Full options

Need larger than 8"? The MOH is not available beyond 8". See the HAC inline series — HAC-50/51 covers 6"–12".

2

Select action — PO or PC

Action is factory-set and cannot be changed after installation. PO is standard for intake applications. Confirm the fail-safe requirement before ordering — if unsure, call technical support.

PO — Power Open

STANDARD

Opens when 24 Vac is applied. Spring-closes on power loss — seals at the wall between cycles.

✓ Fresh air intake — all ventilation applications
✓ Combustion air intake — use with ADP interlock
✓ Exhaust where closed fail-safe on power loss is required

PC — Power Close

Closes when 24 Vac is applied. Spring-opens on power loss — duct remains open if power is lost.

✓ Exhaust where open fail-safe on power loss is required
✓ Control sequences requiring close-on-demand

Application

Action

Fail-Safe

Notes

Fresh air intake

PO

Spring-closes

Standard for all intake

Combustion air intake

PO

Spring-closes

Use with ADP interlock

Exhaust — fail open

PC

Spring-opens

Open fail-safe required

Exhaust — fail closed

PO

Spring-closes

Closed fail-safe required

3

End switch — optional, but required for combustion air interlock

The end switch proves blade position — it closes when the blade physically reaches full open or full closed and sends a confirmation signal to the connected control device. On combustion air applications using an ADP relay adaptor, the end switch is required — without it, the ADP has no position confirmation signal and the interlock sequence cannot function.

Without end switch

Damper operates — no position confirmation output. Use when no interlock circuit or fault detection is required.

Part code: O (e.g. OPO, OPC)

With end switch

Confirms blade has physically reached position. Required for ADP combustion air interlock. Also used when fault detection is needed in a control sequence.

Part code: S (e.g. SPO, SPC)

⚠

For combustion air interlock via ADP relay adaptor: end switch is required. Order MOH with end switch option (SPO action code). The ADP uses the end switch signal to confirm damper position before allowing the appliance to fire.

HOW TO READ YOUR PART NUMBER

MOH

Product

–
06

Size (6")

10

Motor code

–
S

S=end switch

PO

Action

SIZE CODES

04=4" · 05=5" · 06=6" · 07=7" · 08=8"

MOTOR CODE

10=no relay (standard on all MOH)

END SWITCH

O=no end switch · S=end switch included

ACTION

PO=Power Open · PC=Power Close

COMBUSTION AIR + ADP

MOH-0610-SPO

6" · no relay · end switch · Power Open

FRESH AIR — NO INTERLOCK

MOH-0610-OPO

6" · no relay · no end switch · Power Open

EXHAUST — FAIL OPEN

MOH-0610-OPC

6" · no relay · no end switch · Power Close

Why Hoyme

The Same Drive That Powers the HAC and HOM — at the Wall

Generic motorized termination dampers use commodity actuators with circuit-protection rather than stall-protection. On a wall penetration facing freeze-thaw cycling — which is every installation in Canada and the northern U.S. — that distinction matters.

Patented Hoyme Spring Motor Drive

The same 24 Vac, 5-watt stall-protected Synchron motor and nylon bearing assembly used across the HAC and HOM lineup — proven in residential and light commercial installations across Canada and the northern U.S. One drive family, consistent behaviour, consistent service parts across your entire Hoyme specification.

Stall-protected — not circuit-protected
A circuit-protected actuator trips on ice load and leaves the blade position unknown. The Hoyme drive holds against the load without tripping — clears the obstruction when conditions change and returns to normal operation.
Nylon bearing assembly
Engineered for freeze-thaw cycling and cold temperature exposure at the building exterior — not an indoor mechanical room product pressed into wall service.
Serviceable in place
Replacement motor kits stocked at Hoyme wholesalers. A motor failure does not require replacing the complete MOH assembly — the same service parts used across the HAC and HOM lineup apply here.
CSA certified — complete assembly
Certification covers the MOH motor, blade, housing, and all listed configurations — not just the actuator. Most competitive products carry actuator-only certification. For an AHJ who checks, that distinction matters.

Certified. Warranted. Consistent with Your Hoyme Specification.

CSA certified — complete assembly
Motor, blade, housing, and all listed configurations — not actuator-only
2-year electrical · 10-year mechanical warranty
Motor kits stocked at wholesalers — serviceable in place
Adjustable sleeve 7½"–14" · flashing included
Accommodates standard wall assemblies without custom fabrication
Same drive family as HAC and HOM
One service part across your entire Hoyme specification — motor kits, microswitch kits, spring return kits
Rated for low-temperature air — outdoor applications
Engineered for Canadian and northern U.S. climate installations

Key Specs at a Glance

Voltage
24 Vac · 5W
Sizes
4", 5", 6", 7", 8"
Motor
Synchron — stall-protected
Action
PO or PC — specify at order
End Switch
Optional — required for ADP interlock
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 MOH vs. Generic Motorized Termination Hood
Generic Motorized Hood
Commodity actuator — circuit-protected, trips on ice load, leaves blade position unknown
Actuator certified only — damper body and housing typically not covered
Motor failure requires full unit replacement — no serviceable parts
Different drive family from other dampers on the job — separate service parts
Hoyme MOH
Patented stall-protected Synchron motor — holds under ice load, clears when conditions change
CSA certified — complete assembly including motor, blade, and housing
Motor kits serviceable in place — stocked at Hoyme wholesalers
Same drive as HAC and HOM — one service part across your entire Hoyme specification

Shop MOH Dampers

Order Your MOH

PO is standard for most applications. Add the end switch if combustion air interlock via ADP is required — confirm before ordering, action and end switch are factory-set.

Hoyme MOH Motorized All-Weather Hood Damper
CSA Certified Seals at the Wall
MOH Motorized All-Weather Hood Damper
24 Vac  ·  4"–8"  ·  PO or PC  ·  End switch option  ·  Hood + damper + sleeve + flashing — one unit  ·  Fresh air, combustion air, make-up air, HRV/ERV
Shop MOH →

Quick Reference — Order by Application

PO — No End Switch Most Common
Fresh air · HRV/ERV · Make-up air
Power Open · spring-closes on power loss · no interlock circuit needed · e.g. MOH-0610-OPO
PO — With End Switch
Combustion air — ADP interlock
Power Open · end switch proves open · required for ADP relay adaptor interlock · e.g. MOH-0610-SPO
PC — Power Close
Exhaust — open fail-safe
Power Close · spring-opens on power loss · open fail-safe required · e.g. MOH-0610-OPC

For Combustion Air Applications — Order with MOH

ADP-0240-S5A 24 Vac Relay Adaptor
Gas furnace · 24 Vac
ADP-0240-S5A
Most common combustion air interlock · order MOH with end switch
ADP-0MV2-S5A Millivolt Relay Adaptor
Millivolt furnace · standing pilot
ADP-0MV2-S5A
Only model rated for millivolt safety circuits · order MOH with end switch
OOH All-Weather Inlet Hood — passive, no motor
No motor needed? See passive option
OOH All-Weather Inlet Hood
Passive termination — no motor, no wiring, fixed or Velcro screen · 4"–12"
Not sure which configuration is right for your job?
Call technical support with your application, duct size, and wall thickness — we'll confirm the right MOH and whether ADP interlock is required before you order.

COMMON QUESTIONS

MOH Motorized Hood FAQs

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

What's the difference between the MOH and a standard hood with a HAC inline damper? +

The MOH seals at the wall — there's no duct run between the damper blade and the building exterior. A standard hood with a HAC inline damper seals wherever the HAC is installed in the duct, leaving the duct segment between the HAC and the exterior open to outdoor air when the damper is closed.

In northern climates, that duct segment is a cold air column every time the system cycles off. The MOH eliminates it. The HAC is the right choice when the damper needs to be located somewhere in the duct run rather than at the wall, or when an existing hood is already in place and adding an inline damper is simpler than replacing the hood entirely.

Use MOH when:

Wall penetration is the natural control point · new installation · no existing hood

Use HAC when:

Existing hood in place · control point is in the duct run · need insulated body or heat bypass

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

Both are CSA-certified motorized dampers on the same Hoyme patented drive. The difference is installation point.

MOH — at the wall

Combined motorized damper and all-weather hood. Mounts at the wall penetration — hood and damper in one unit at the building exterior.

HOM — in the duct run

Inline combustion air damper. Installs in the duct run — exterior termination handled separately by OOH or existing hood.

For combustion air applications, the choice is usually driven by wall construction and installation access. If combining the hood and damper at the exterior wall is preferred, use the MOH. If the control point belongs in the duct run, use the HOM.

When would I use PC instead of PO? +

PO (Power Open) is the standard for all intake applications — fresh air, combustion air, HRV/ERV, make-up air. The damper is spring-closed at rest and opens when 24 Vac is applied. On power loss it spring-closes, sealing the wall penetration. PO is also used on exhaust applications where a closed fail-safe on power loss is required.

PC (Power Close) is used on exhaust applications where the control sequence requires the damper to close on demand and the fail-safe position is open — for example, an exhaust system where the duct must remain passively open if power is lost.

If you're unsure which action is right for your sequence, use PO for intake and confirm the fail-safe requirement for exhaust with technical support before ordering — action cannot be changed after installation.

Do I need the end switch option? +

The end switch proves blade position — it closes when the blade physically reaches its full open or closed position and sends a signal to the connected control device. It does not operate the motor. The 24 Vac supply operates the motor. The end switch is wired separately to the interlock circuit, safety control, or BAS input.

End switch NOT required

Fresh air ventilation, HRV/ERV, make-up air where no interlock circuit or fault detection is needed

End switch REQUIRED

Combustion air interlock via ADP relay adaptor — the ADP uses the end switch signal to confirm proved-open before allowing the appliance to fire

What ADP relay adaptor do I need for combustion air interlock? +

Select by appliance type and system voltage. The MOH end switch option is required on all combustion air interlock applications — order the MOH with end switch (SPO action code).

ADP-0MV2-S5A

Millivolt furnace — standing pilot, thermopile or thermocouple safety system

ADP-0240-S5A

24 Vac furnace — electronic ignition · most common

See the ADP series page for the full model lineup including boiler, tankless water heater, and gas dryer applications.

What wall thickness does the MOH accommodate? +

The adjustable extension sleeve included with the MOH accommodates wall thicknesses from 7½" to 14" ('L' dimension). This covers standard 2×4 and 2×6 framing with typical exterior cladding and interior drywall.

For walls outside this range — mass masonry, thick stucco systems, ICF construction — confirm clearance before ordering and contact technical support if a non-standard extension length is required.

The motor assembly mounts on the interior side of the wall — plan interior clearance for the motor housing and wiring before cutting the wall opening. Flashing for siding or stucco installation is included in every box — confirm compatibility with your exterior cladding type before cutting.

Can the MOH be used for dryer exhaust? +

No. The dryer exhaust environment — elevated temperature, lint, high humidity — is outside the MOH's listed application. Lint accumulation in the motor assembly causes premature failure.

Use the Hoyme BDH Back Draft Hood for dryer exhaust terminations — available in spring-close and gravity-close configurations with optional end switch for proving circuits.

Does the screen need to be removed for exhaust applications? +

Yes. The ¼" screen ships installed for intake applications. Remove the screen before installation on exhaust applications — leaving the screen in place on exhaust will cause backpressure and performance issues as the screen restricts airflow in the exhaust direction.

The screen removal is covered in the installation instructions included in the box.

Who do I call if I'm unsure which product or configuration is right? +

Call Hoyme technical support directly. Have your application, duct size, wall thickness, and whether a hood is already in place ready — the call is typically under five minutes and we'll confirm whether MOH, HAC, or HOM is the right product and which configuration to order.

READY TO ORDER

Sealed at the Wall. First Time. No Callbacks.

Shop the MOH directly, or call technical support with your application, duct size, and wall thickness — we'll confirm the right configuration and whether ADP interlock is required before you order.

✓ CSA certified — complete assembly
✓ Seals at the wall — no cold air column in the duct
✓ Hood + damper + sleeve + flashing — one unit
✓ Same Hoyme drive as HAC and HOM — one service part
✓ 2-yr electrical · 10-yr mechanical warranty