Ductwork Calculator Project Checklist

Introduction

Ductwork gets buried — behind drywall, above ceilings, under insulation — which makes the pre-close-up inspection the last cheap chance to catch mistakes. A crushed flex run or a missing damper costs minutes to fix at rough-in and hours (plus drywall repair) after concealment. This checklist walks through verification in the order a job unfolds: design review, rough-in checks, sealing and insulation, and final commissioning. Print it, walk the job with it, and check every box before concealment. The sizes it references come from the Ductwork Calculator; the reasoning behind each check is in the complete guide.

Phase 1 — Design Review (Before Buying Material)

• Room-by-room CFM values documented from load calculations (not square-footage guesses).
• Every branch sized: CFM ÷ target velocity → area → diameter, rounded up to the next standard size.
• Actual velocity rechecked per run: 600–900 FPM (3.0–4.6 m/s) supply branches, 600–700 FPM (3.0–3.6 m/s) returns.
• Trunk stepped down as branches peel off; each segment sized for its remaining CFM.
• Total equivalent length computed for the longest run — every takeoff (35 ft / 10.7 m), elbow, transition, and boot counted.
• Design friction rate = (available static ÷ TEL) × 100 lands in the 0.08–0.10 in w.g./100 ft (0.65–0.82 Pa/m) band.
• Return side sized at least as generously as supply; every closed room has a return path.
• Material specified per section (metal trunk, flex branches ≤25 ft / 7.6 m) — sized in the material being installed, per the material guide.
• Balancing damper at every supply takeoff — on the plan and in the material order.
• Permit requirements confirmed with the AHJ; see the code compliance guide.

Phase 2 — Rough-In (Before Sealing)

• Trunk hung at the specified size per segment; transitions gradual (≤45°).
• Takeoffs installed with dampers, sealed collars — no raw cut holes with flex stuffed over.
• Flex runs: inner core fully stretched, cut to exact length (no coils of excess), bends ≥ one duct diameter radius.
• Flex supported every 4 ft (1.2 m) with wide straps; sag within limits; no kinks at takeoffs or boots.
• Metal duct supported per schedule without pinching or ovalizing; hangers cradle, don’t cinch.
• Elbows minimized; square elbows fitted with turning vanes where specified.
• Boots secured and sized to the run CFM; grilles on hand to verify fit.
• Return ducts, filter rack, and grilles installed — return side not left for “later.”
• Fire dampers installed where ducts penetrate rated assemblies, with access.
• Clearances maintained at equipment, flues, and heat sources.

Phase 3 — Sealing and Insulation (Before Concealment)

• Every joint, seam, takeoff, and boot connection sealed with mastic (or UL-181-listed tape) — brushed ≥2 in (50 mm) wide over fitted joints.
• Flex inner cores sealed to collars before jackets pulled over; jackets inspected for tears and taped.
• Insulation at specified R-value for the location (commonly R-8 attics, R-6 other unconditioned spaces — verify locally).
• Vapor jackets intact and sealed; no compressed insulation at straps.
• Duct board joints sealed per manufacturer spec; interior liner unbroken.
• Access panels installed at every balancing damper and serviceable component.
• Penetrations through the thermal envelope sealed (not just insulated over).
• Photos taken of everything before close-up — the only record you’ll ever have.

Phase 4 — Commissioning (After Equipment Start-Up)

• Blower speed set per equipment specs; total external static pressure measured and within rating.
• Dampers balanced room to room; far rooms verified for airflow, not just near ones.
• Register throw checked — air should mix the room, not dribble or blast.
• Noise check at every grille; velocities above ~900 FPM (4.6 m/s) investigated.
• Duct leakage test performed where code requires; results documented.
• Filter installed, rack sealed, replacement size/schedule communicated.
• Thermostat operation verified in all modes; no room more than ~2–3°F (1–1.5°C) from setpoint under steady conditions.
• As-built sketch updated (damper positions marked) and left with the system documentation.
• Customer walkthrough completed: filter location and change schedule, damper access points, thermostat basics, and who to call for service explained.

Commonly Skipped Items (Don’t)

1. Dampers — the #1 value-engineered item and the #1 source of unfixable imbalance. The common mistakes guide covers the consequences.
2. Return paths for closed rooms — pressurized bedrooms, starved system.
3. Leakage testing — “looks sealed” isn’t a measurement.
4. Photos before close-up — free, takes minutes, invaluable forever.
5. Balancing — installation without commissioning is unfinished work.

Related Guides

• Complete Guide — the sizing method behind the checklist.
• Pro Tips — installation practices the checklist verifies.
• Common Mistakes — what each check prevents.
• Code Compliance — inspection items by code.
• FAQ — quick answers to sizing questions.

Frequently Asked Questions

When should I inspect ductwork?

Three times: design review before buying material, rough-in before sealing and concealment, and commissioning after equipment start-up. The rough-in inspection is the critical one — it’s the last chance to fix cheaply.

What should I photograph before drywall?

Everything: trunk runs with visible sizes, every takeoff and damper, flex supports and bends, sealed joints, insulation labels showing R-value, and access panel locations. Store with the house documents.

How do I verify airflow to each room?

A balometer/hood at each grille is the proper tool; a handheld anemometer gives reasonable spot checks. Compare against the design CFM per room — within ~10% is a well-balanced system.

What static pressure should the system run at?

At or below the equipment’s rated total external static pressure (commonly 0.50 in w.g. residential). Higher readings mean the ducts are too restrictive — find the restriction rather than raising blower speed.

Final Sign-Off

A duct system passes when the paperwork, the installation, and the measurements agree: sized per the Ductwork Calculator and Manual D methods, installed per the checklist, and commissioned to measured airflow. Check every box, keep the photos, and the system behind the drywall will be the system you designed.

Disclaimer: This checklist is general planning guidance, not a substitute for professional inspection or code compliance verification. Follow your local mechanical code, obtain required permits and inspections, and consult a licensed HVAC professional for system design and commissioning decisions.