TryBuildCalc

Combustion & Makeup Air Sizing Verification Checklist

Essential Checklist+

Complete these critical checks before approving the work or proceeding to the next construction stage.

✓17 Inspection Points
✓4 Verification Categories
✓Appliance Load & Space Check+
  • Every atmospheric/open-combustion gas appliance actually sharing this room or closet is included in the appliance list, not just the primary furnace/boiler
  • Confirmed no listed appliance is actually a sealed-combustion (direct-vent) unit, which draws combustion air from outdoors through its own dedicated intake and should NOT be counted here
  • Each appliance's entered value is its Btu/hr INPUT rating (nameplate), not its output/AFUE-adjusted capacity
  • Room volume reflects the actual enclosed space boundaries (walls, ceiling, permanent partitions), not the whole basement or building it opens into
✓Opening Method Selection+
  • Selected opening method (indoor, outdoor two-opening, outdoor single-opening, or mechanical) actually matches what's physically achievable at this specific installation
  • If using the indoor two-opening method, confirmed the additional indoor space is on the SAME STORY as the appliance space — not a different story
  • If using the single-opening method, verified — not assumed — that every appliance in the space actually has a draft hood or is fan-assisted Category I, and meets its required clearances
  • For an outdoor two-opening installation actually using ductwork, confirmed whether that duct run is genuinely vertical or horizontal — and used the correct correspondingly-sized opening
  • For the single-opening method, the entered vent connector area reflects the actual combined draft-hood/flue-collar outlet areas of the appliances, not a placeholder zero
  • If choosing the mechanical combustion air supply alternative, confirmed the interlock (preventing appliance burner operation whenever the mechanical air supply isn't running) is part of the installation plan
✓Louver/Grille & Installation+
  • Louver/grille type selected matches the actual product being installed, checked against its manufacturer spec sheet's published free area once a specific model is chosen
  • For any two-opening method, confirmed one opening will actually be located within 12 in of the top of the enclosure and the other within 12 in of the bottom
  • Every planned opening's actual width and height (not just its area) checked to be at least 3 in in every cross-sectional dimension
  • If a motorized damper or louver is used instead, confirmed it's interlocked with the appliance(s) so the main burner can't fire until it's proven fully open
✓After-Installation Verification+
  • As-built opening sizes measured and confirmed to actually meet or exceed this calculator's required free/gross area — not just assumed correct from the original plan
  • Checked for signs of backdrafting or spillage at the draft hood (using a mirror, smoke pencil, or combustion analyzer) with all exhaust fans/appliances operating simultaneously
  • A working carbon monoxide alarm is installed near the appliance space and in relevant living areas, independent of whether this calculation was applied correctly
Full QC Checklist+

Verify appliance load and space check, opening method selection, louver/grille and installation, and after-installation verification for combustion/makeup air sizing.

✓22 Inspection Points
✓4 Verification Categories
✓Appliance Load & Space Check+
  • Every atmospheric/open-combustion gas appliance actually sharing this room or closet is included in the appliance list, not just the primary furnace/boiler
  • Confirmed no listed appliance is actually a sealed-combustion (direct-vent) unit, which draws combustion air from outdoors through its own dedicated intake and should NOT be counted here
  • Each appliance's entered value is its Btu/hr INPUT rating (nameplate), not its output/AFUE-adjusted capacity
  • Room volume reflects the actual enclosed space boundaries (walls, ceiling, permanent partitions), not the whole basement or building it opens into
  • Room volume calculation doesn't inflate the usable volume with space effectively unavailable due to built-in shelving, ductwork, or other fixed obstructions
  • Tight construction answered honestly based on the building's actual weatherization (not just its age) — newer, energy-retrofitted, or superinsulated homes often qualify even if not architecturally modern
✓Opening Method Selection+
  • Selected opening method (indoor, outdoor two-opening, outdoor single-opening, or mechanical) actually matches what's physically achievable at this specific installation
  • If using the indoor two-opening method, confirmed the additional indoor space is on the SAME STORY as the appliance space — not a different story
  • If using the single-opening method, verified — not assumed — that every appliance in the space actually has a draft hood or is fan-assisted Category I, and meets its required clearances
  • For an outdoor two-opening installation actually using ductwork, confirmed whether that duct run is genuinely vertical or horizontal — and used the correct correspondingly-sized opening
  • For the single-opening method, the entered vent connector area reflects the actual combined draft-hood/flue-collar outlet areas of the appliances, not a placeholder zero
  • If choosing the mechanical combustion air supply alternative, confirmed the interlock (preventing appliance burner operation whenever the mechanical air supply isn't running) is part of the installation plan
✓Louver/Grille & Installation+
  • Louver/grille type selected matches the actual product being installed, checked against its manufacturer spec sheet's published free area once a specific model is chosen
  • For any two-opening method, confirmed one opening will actually be located within 12 in of the top of the enclosure and the other within 12 in of the bottom
  • Every planned opening's actual width and height (not just its area) checked to be at least 3 in in every cross-sectional dimension
  • Both openings positioned where they won't be blocked by stored items, furniture, or future renovation — not just clear at the time of installation
  • Any nonmotorized louver or grille installed is fixed permanently in the open position, not adjustable/closable by an occupant
  • If a motorized damper or louver is used instead, confirmed it's interlocked with the appliance(s) so the main burner can't fire until it's proven fully open
✓After-Installation Verification+
  • As-built opening sizes measured and confirmed to actually meet or exceed this calculator's required free/gross area — not just assumed correct from the original plan
  • Checked for signs of backdrafting or spillage at the draft hood (using a mirror, smoke pencil, or combustion analyzer) with all exhaust fans/appliances operating simultaneously
  • A working carbon monoxide alarm is installed near the appliance space and in relevant living areas, independent of whether this calculation was applied correctly
  • Local jurisdiction's adopted code edition and any local amendments checked directly, especially for the tight-construction-unconfined case this calculator flags as needing local verification
Inspection Notes+
Use the latest approved drawings, specifications, and site measurements.
Complete all critical checks before proceeding to the next work stage.
Record deviations and confirm rectification where required.

Related Calculators & Guides

Combustion & Makeup Air Sizing CalculatorOpen the related calculator and verify the current project inputs.

FAQ

Use it after collecting the project inputs and again before approving or closing the relevant work stage.
No. It supports verification but does not replace approved drawings, specifications, codes, manufacturer requirements, or professional inspection.