Technical Reference
Code-Compliant HVAC Dampers
for Canada & the United States
Hoyme motorized dampers help contractors, builders, and inspectors meet Canadian and U.S. air, fuel, and energy codes including MNECH, NECB, CSA B149, CSA B139, and state-by-state U.S. standards.
Why It Matters
Why Combustion-Air & Fresh-Air Codes Matter
Modern building codes across Canada and the United States are tightening. Passive combustion-air openings and always-open ducts:
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Waste heat — cold air enters standby ducts every hour the appliance isn't running, driving up heating costs
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Create negative building pressure — uncontrolled airflow causes backdrafting, drafts, and cold spots
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Create safety risk — homeowners block passive openings; without interlock, appliances fire without a proved-open combustion air path
Codes such as CSA B149.1 (Natural Gas & Propane), CSA B139 (Oil-Burning Equipment), and the Model National Energy Code for Houses (MNECH) all point toward the same requirements:
✓ Use Motorized, Automatic Dampers
Manual dampers are not permitted in combustion-air ducts. The damper must open and close automatically with the appliance.
✓ Interlock the Damper with the Appliance
The burner cannot fire unless the damper end switch confirms it is fully open. The HOM's internal relay handles this interlock when wired per the included diagrams.
✓ Size the Duct Correctly for Total BTU Input
Proper combustion-air sizing based on total appliance BTU input is required for safe and code-compliant operation.
Hoyme dampers were designed around these exact principles. For over 40 years, inspectors, utilities, and contractors have relied on Hoyme products to meet code, improve comfort, and reduce wasted energy. This is why inspectors recommend Hoyme.
Code Reference
What the Building Codes Require (Explained Simply)
CSA B149.1 — Natural Gas & Propane Combustion Air
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The CSA B149.1 code requires that combustion air for gas and propane appliances:
✓Must not be restricted or blocked
✓Must be sized correctly based on total appliance BTU input
✓Must not use manual dampers in the combustion air duct
✓Must use automatic dampers that are interlocked — the appliance cannot fire until the damper is fully open
✓Must use CSA-certified dampers when installed inside a dwelling
Hoyme Alignment
→HOM SO2 — CSA-certified motorized combustion-air damper with end switch, 4"–9", 24 Vac. For a single 24Vac furnace, the HOM wires directly to the appliance control circuit — no external ADP required (see included wiring diagrams).
→ADP-0243-S5A — required when one HOM damper serves two separate 24Vac appliances; proves damper open before either appliance fires
→ADP-0MV2-S5A — millivolt or standing-pilot appliances (250mVdc–100Vdc safety circuits)
→HAC + ADP-0241-S5A — for fresh-air ventilation intakes; opens damper first, confirms position, then energizes furnace fan to prevent cold air dump into the living space
CSA B139 — Oil-Burning Equipment
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CSA B139 requires that any damper installed in a combustion air duct for oil-burning equipment:
✓Must be automatic — no manual blades
✓Must be interlocked — the burner cannot fire until the damper is fully open
Hoyme Alignment
→HOM SO2 — approved for oil-fired equipment when installed and interlocked per manufacturer's wiring diagrams. Size at approximately 1 in² per 5,000 BTU for oil.
→ADP-1102-S5A (up to 5A oil burner, 110 Vac) or ADP-1102-10A (larger 110 Vac load) — oil burner interlock relay
MNECH & NECB — Energy Codes for Houses and Buildings
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The MNECH and NECB require controlled airflow at key duct penetrations to reduce standby heat loss:
✓Motorized dampers on outdoor air intake ducts
✓Motorized or backdraft dampers on exhaust air outlets
✓Controlled combustion air and ventilation air to reduce standby heat loss
Hoyme Alignment
→HOM SO2 — satisfies combustion-air inlet damper requirements
→HAC + ADP-0241-S5A — controls fresh-air ventilation intake and sequences damper open before furnace fan energizes, preventing cold air dump at registers
→HAC-F — motorized flue damper reduces standby flue heat loss and supports energy-efficiency targets
IRC / IECC / NFPA — U.S. Combustion Air & Ventilation
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Most U.S. states adopt versions of the IRC, IECC, and NFPA fuel codes. Across these standards the requirements are consistent:
✓Combustion air openings must be sized correctly by total BTU — typically 1 in² per 4,000 BTU in U.S. codes
✓Manually operated dampers are not permitted in combustion air ducts
✓Interlocks are required — appliances cannot fire without a proved-open combustion air path
Hoyme Alignment
→HOM SO2 — CSA certified, used throughout the U.S. to satisfy IRC/IECC combustion air requirements; wires directly to 24Vac furnace per included wiring diagrams
→HAC + ADP-0241-S5A — fresh-air ventilation damper with furnace fan sequencing for mechanical ventilation code compliance
By Region
Province / Region Guide
Select your province or region to see what inspectors expect, what code requires, and the correct Hoyme products for your installation.
British Columbia
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BC adopts the BC Building Code (BCBC) referencing CSA B149.1 for gas appliances and MNECH for energy efficiency. Inspectors enforce airtight construction and controlled ventilation strictly — passive combustion-air openings routinely fail. HRV/ERV intakes must also be controlled.
What Inspectors Expect in BC
→Motorized, interlocked combustion-air damper per CSA B149.1
→Controlled mechanical ventilation intake — damper sequences before furnace fan
→HRV/ERV intakes must be controlled — not left open when unit is off
→No manual dampers in combustion air ducts — passive hoods fail inspection
Correct Hoyme Products for BC
→HOM SO2 — CSA-certified combustion-air damper, 4"–9"; wires directly to 24Vac furnace per included diagrams — no ADP required for single-furnace installation
→ADP-0MV2-S5A — add only if appliance is millivolt/standing pilot
→HAC + ADP-0241-S5A — ventilation/HRV/ERV damper with furnace fan sequencing
→HAC-F — optional flue damper for additional energy efficiency credit under MNECH
Quick Pick — Most BC Homes
Alberta
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Alberta adopts CSA B149.1 through the Alberta Building Code. Inspectors do not accept passive combustion air in new construction — the damper must be motorized, CSA certified, and interlocked with an end switch proving sequence. This is Hoyme's core market. Cold climate insulated variants (HAC-L, HAC-12L) are strongly recommended for fresh-air intakes in exterior walls.
What Inspectors Expect in Alberta
→Motorized, CSA-certified combustion-air damper — passive hoods fail inspection
→Mandatory end-switch interlock — furnace cannot fire until damper confirms open
→Mechanical ventilation (HRV/ERV) intake must also be controlled
→Cold climate — insulated dampers recommended to prevent condensation
Correct Hoyme Products for Alberta
→HOM SO2 — CSA-certified combustion-air damper; wires directly to 24Vac furnace — no ADP required for single-furnace installation
→ADP-0MV2-S5A — add only if appliance is millivolt/older standing-pilot furnace
→HAC-L — upgrade to insulated body for exterior wall or unconditioned space installs
Quick Pick — 99% of Alberta Homes
Saskatchewan
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Saskatchewan adopts CSA B149.1 through the Saskatchewan Building Code. Extreme winters mean heat loss through passive openings is significant — inspectors require motorized, interlocked dampers on all new construction. Insulated variants strongly recommended due to extreme cold.
What Inspectors Expect in Saskatchewan
→Motorized combustion-air damper per B149.1
→Interlock to furnace or boiler — end switch proving required
→Controlled ventilation intake — insulated damper recommended for exterior walls
Correct Hoyme Products for Saskatchewan
→HOM SO2 — combustion-air damper; wires directly to 24Vac furnace — no ADP required for single-furnace installation
→ADP-0MV2-S5A — add only if appliance is millivolt/standing pilot
→HAC-L + ADP-0241-S5A — insulated ventilation damper recommended for Saskatchewan winters
→HAC-H — heat bypass variant for single-speed furnace zone control in extreme cold
Quick Pick — Saskatchewan
Manitoba
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Manitoba adopts CSA B149.1 through the Manitoba Building Code. Cold winters and decades of backdrafting issues mean both new construction and retrofits require controlled combustion air and ventilation. Insulated dampers are standard practice for exterior wall installations.
What Inspectors Expect in Manitoba
→Motorized combustion-air damper per B149.1
→Interlock to furnace — no fire without proved-open damper
→Controlled ventilation intake — insulated recommended for exterior wall
Correct Hoyme Products for Manitoba
→HOM SO2 — combustion-air damper; wires directly to 24Vac furnace — no ADP required for single-furnace installation
→ADP-0MV2-S5A — add only if appliance is millivolt/standing pilot
→HAC-H — heat bypass for freeze protection in extreme cold applications
Ontario
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Ontario Building Code references CSA B149.1 — combustion air must be controlled and interlocked on all permitted residential installations. The HOM is the standard solution recognized by Ontario inspectors. Millivolt systems (older homes) are common in Ontario — confirm furnace type before selecting ADP model.
What Inspectors Expect in Ontario
→Motorized, CSA-certified combustion-air damper
→Mandatory interlock — end switch proving sequence required
→Controlled mechanical ventilation — no manual dampers
Correct Hoyme Products for Ontario
→HOM SO2 — combustion-air damper; wires directly to 24Vac furnace — no ADP required for single-furnace installation
→ADP-0MV2-S5A — add if appliance is millivolt/older standing-pilot furnace (common in Ontario retrofit)
→HAC-F — flue damper for gas fireplace standby heat loss reduction
Quick Pick — Ontario (24Vac Furnace)
Atlantic Canada
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Oil-fired systems dominate Atlantic Canada. CSA B139 requires interlocked combustion-air dampers for all oil equipment — the ADP must be matched to the 110 Vac oil burner control circuit, not the standard 24 Vac furnace relay. Confirm appliance load before selecting ADP model — oil burners vary between 5A and 10A.
What Inspectors Expect in Atlantic Canada
→Interlocked combustion-air damper — mandatory for all oil equipment under CSA B139
→Automatic damper only — no manual blades permitted
→Size at approximately 1 in² per 5,000 BTU for oil — confirm with AHJ
Correct Hoyme Products for Atlantic Canada
→HOM SO2 — approved for oil-fired equipment when interlocked per manufacturer wiring diagrams
→HAC + ADP-0241-S5A — where mechanical fresh air or HRV ventilation is also required
Quick Pick — Atlantic Canada (Oil)
Cold Climates (MN, WI, MI, ND, MT, ME)
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Cold U.S. states adopt the IRC and IECC requiring fully controlled combustion air on sealed construction. The HOM is CSA certified and widely recognized by northern U.S. inspectors. Insulated variants (HAC-L) are strongly recommended for exterior wall fresh-air intakes in these climates.
What Inspectors Expect
→Motorized, interlocked combustion-air damper per IRC
→Sizing at 1 in² per 4,000 BTU — confirm with local AHJ
→No manual dampers — insulated dampers recommended for exterior walls
Correct Hoyme Products
→HOM SO2 — CSA-certified combustion-air damper; wires directly to 24Vac furnace — no ADP required for standard single-furnace installation. For boiler/110Vac use ADP-1102-S5A.
→HAC-L + ADP-0241-S5A — insulated ventilation/HRV intake damper with furnace fan sequencing
→HAC-H — heat bypass option for freeze prevention in extreme cold applications
Mixed Climates (PA, VA, CO, OR, WA)
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Mixed-climate states follow IRC/IECC requiring controlled combustion air and mechanical ventilation dampers on sealed construction. The standard HAC with ADP relay is the right solution — insulated variants are not typically required but recommended for CO and higher elevation installations with significant temperature swings.
What Inspectors Expect
→No manual combustion-air dampers
→Controlled mechanical ventilation damper — sequences before furnace fan
→Interlock when combustion air is ducted — confirm with local AHJ
Correct Hoyme Products
→HOM SO2 — when combustion air is ducted; wires directly to 24Vac furnace per included diagrams
→HAC + ADP-0241-S5A — fresh-air ventilation damper with furnace fan sequencing
→HAC-L — upgrade to insulated for CO, high-altitude, or exterior wall installations
Quick Pick — Mixed Climates
Warm States (TX, FL, GA, AZ, CA)
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Warm-climate states require controlled mechanical ventilation for indoor air quality and humidity control. Where fuel-burning appliances use ducted combustion air, interlock is still required. The standard HAC without insulation is the right product — cold climate variants are not needed in these markets.
What Inspectors Expect
→Controlled fresh-air inlet on mechanical ventilation — ASHRAE 62.2
→Combustion-air damper and interlock where ducted combustion air applies
→No passive openings on sealed/tight construction
Correct Hoyme Products
→HAC + ADP-0241-S5A — primary product for fresh-air mechanical ventilation with furnace fan sequencing
→HAC-12 — 120 Vac version for line-voltage systems, no transformer needed
→HOM SO2 — only where ducted combustion air is required; wires directly to appliance per included diagrams
Sizing Reference
How to Size a Combustion Air Damper
CSA B149.1 requires combustion air openings to be sized based on total appliance BTU input. Use this table as a general guide for natural gas and propane systems. The duct area values shown are based on 1.0 sq. in. per 7,000 BTUH per Hoyme's installation guidelines. For oil-fired or U.S.-specific requirements, see the notes below or check with your local inspector.
| Total Input (BTU/h) |
Duct Opening Area (sq. in.) |
Recommended Size |
Typical Application |
| Up to 88,000 |
12.6 (4" round) |
4" HOM → |
Small single appliance |
| Up to 137,000 |
19.6 (5" round) |
5" HOM → |
Single residential furnace or furnace + water heater |
| Up to 198,000 |
28.3 (6" round) |
6" HOM → |
Two appliances sharing one combustion air duct |
| Up to 269,000 |
38.5 (7" round) |
7" HOM → |
Multiple appliances or light commercial |
| Up to 352,000 |
50.3 (8" round) |
8" HOM → |
Small mechanical rooms with several appliances |
| Up to 400,000 |
63.6 (9" round) |
9" HOM → |
Larger mechanical rooms — commercial modules available above 400,000 BTU |
Sizing basis: 1.0 sq. in. of round duct cross-section per 7,000 BTUH of total appliance input per Hoyme installation guidelines. Always confirm the applicable local code sizing rule with your AHJ before installation.
Oil-fired appliances: many jurisdictions use approximately 1 in² per 5,000 BTU.
U.S. states: some codes use up to 1 in² per 4,000 BTU — always confirm with the local authority having jurisdiction (AHJ).
Important: size the HOM to the combustion air duct diameter. Order with end switch (SO2 variant) for interlock proving sequence. For two appliances sharing one HOM, confirm duct area serves total combined BTU input.
Unconditioned space / cold climate: if the fresh-air damper (HAC) is installed in an unconditioned space, near an exterior wall, or in a crawlspace, consider upgrading to the HAC-L → factory-insulated version to prevent condensation at the damper body.
Automatic Motorized
HOM uses Hoyme's patented spring motor drive — 24 Vac, 5W, stall-protected Synchron motor engineered for freeze-thaw cycling on outdoor combustion air intakes.
Interlock Ready
For a single 24Vac furnace, the HOM wires directly — no external ADP required. ADP adaptors (ADP-0243-S5A, ADP-0MV2-S5A, ADP-1102-S5A) are available for two-appliance, millivolt, and oil applications respectively.
CSA Certified
HOM Series is CSA certified for combustion air applications — the complete assembly, not just the motor. Required for permitted installations inside dwellings under CSA B149.1.
Cold Climate Rated
Patented nylon bearing assembly and stall-protected motor handle freeze-thaw cycling and ice loading on combustion air intakes — designed for Canadian and northern U.S. climates.
