TryBuildCalc

Duct Size Verification Checklist

Essential Checklist+

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

✓9 Inspection Points
✓5 Verification Categories
✓Run Inputs & Design Basis+
  • Each run's CFM value pulled from an actual room-by-room ACCA Manual J load calculation, not guessed or evenly split across rooms
  • Duct category selected correctly per run (Supply Trunk / Supply Branch / Return Trunk / Return Branch)
✓Before Fabrication / Design+
  • A full ACCA Manual D duct design obtained from a licensed HVAC contractor before fabrication or installation, not just this velocity shortcut
  • Total effective length (straight duct length + fitting/elbow equivalent lengths) calculated for each run, not skipped
  • Available static pressure budget confirmed against the air handler/furnace's rated external static pressure at the design CFM
✓Installation & Sealing+
  • All duct joints sealed with mastic or UL 181-rated tape, not cloth-backed "duct tape"
  • Flexible duct runs pulled tight and supported, not left looped, kinked, or with excess slack
✓Airflow Verification+
  • Actual airflow at each register measured with a flow hood or anemometer after installation, not assumed from this calculator's target velocity
✓After Installation+
  • Final system static pressure tested against the equipment's rated external static pressure after installation is complete
Full QC Checklist+

Verify run input basis, pre-fabrication design decisions, installation and sealing, airflow verification, and post-installation checks.

✓21 Inspection Points
✓5 Verification Categories
✓Run Inputs & Design Basis+
  • Each run's CFM value pulled from an actual room-by-room ACCA Manual J load calculation, not guessed or evenly split across rooms
  • Duct category selected correctly per run (Supply Trunk / Supply Branch / Return Trunk / Return Branch)
  • Suggested Total System CFM (from tonnage x CFM/ton) compared against the sum of entered supply-trunk run CFM as a sanity check
  • Airflow-per-ton selection (350 / 400 / 450 CFM/ton) matches your actual climate, not left at the default
✓Before Fabrication / Design+
  • A full ACCA Manual D duct design obtained from a licensed HVAC contractor before fabrication or installation, not just this velocity shortcut
  • Total effective length (straight duct length + fitting/elbow equivalent lengths) calculated for each run, not skipped
  • Available static pressure budget confirmed against the air handler/furnace's rated external static pressure at the design CFM
  • Duct material and insulation R-value selected appropriately for its location (e.g. higher R-value for unconditioned attic runs vs. conditioned-space runs)
  • Return air pathway confirmed (dedicated return ducts per room, or transfer grilles/jump ducts) rather than sizing supply runs alone
✓Installation & Sealing+
  • All duct joints sealed with mastic or UL 181-rated tape, not cloth-backed "duct tape"
  • Duct support spacing meets manufacturer/code requirements to prevent sagging over the run's length
  • Flexible duct runs pulled tight and supported, not left looped, kinked, or with excess slack
  • Trunk-to-branch takeoffs installed with proper conical/manufactured fittings, not sharp 90-degree taps cut directly into the trunk
  • Ducts routed through unconditioned spaces (attic, crawlspace, garage) insulated to at least the local code-minimum R-value
✓Airflow Verification+
  • Actual airflow at each register measured with a flow hood or anemometer after installation, not assumed from this calculator's target velocity
  • Total system airflow verified against the equipment's rated CFM at the actual installed duct static pressure, not just its nameplate rating
  • Balancing dampers installed on branches feeding rooms far from the trunk, and adjusted during commissioning
  • Noise levels checked at any run sized close to or at its category's maximum velocity, especially return branches
✓After Installation+
  • Register/grille free-area size matches the actual duct branch feeding it, not left as whatever was pre-installed
  • Final system static pressure tested against the equipment's rated external static pressure after installation is complete
  • All accessible duct joints visually inspected during final walkthrough for missed mastic or tape coverage
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

Duct Size 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.