Two things on this page are wrong and we would rather tell you than let you find out: the friction-rate slider does not change the duct sizes on a typical residential job, because the velocity limit governs instead; and this tool never sizes a return duct at all. Supply airflow is also split evenly across your run count, which real houses do not do.
The calculation engine has not yet been checked against a reference tool on a real house. Treat every number here as a starting point to verify, not a finished answer.
Check the results before you act on them. Verify against the equipment data plate, the manufacturer's installation manual, and your own measurements. You are responsible for what you install — Cheek Heating & Cooling LLC is not liable for decisions made from this tool's output.
Duct sizer
Round duct sizes for a residential system, using the ACCA Manual D® equal-friction method. Tell it the tonnage and how many supplies you are running — it gives you the trunk, the branches, the velocity in each one, and the static pressure the blower has to overcome.
Estimating aid only. Sizes come from the equal-friction method with typical residential assumptions, not from a measured duct layout. Not an ACCA-certified Manual D product (that's a separate ACCA certification program) and not an engineered mechanical drawing — verify duct routing, fitting equivalent lengths, register throw, and blower capability against the manufacturer's install manual and your local code.
How much air?
350 for humid / high-latent jobs, 400 typical, 450 for dry climates or heat pumps.
How many supply runs?
Lower = bigger, quieter duct. 0.08 is the usual residential target.
Longest run from the air handler to the farthest register, plus the equivalent length of every fitting on that run. Measure it when you can.
Deducts the coil, filter, register, grille and damper losses from the blower's rated external static, then sizes the duct on what's left instead of on the friction rate set above.
From the manufacturer's blower table at your design CFM — not the nameplate max. 0.50 is typical for a PSC blower; variable-speed ECM is often 0.50–0.80.
Leave blank for typical residential figures (0.25 wet coil, 0.10 clean 1" pleated filter, plus registers, grille and damper). In this mode the friction-rate slider is ignored — the rate is derived from what the blower has left. Make sure the equivalent length above covers the longest supply run plus the return.
The work
Every section, so you can check it and defend it.
| Section | CFM | Round | Velocity | Friction /100 ft |
|---|---|---|---|---|
Static pressure
- Design friction rate
- derived
- Effective length
- Duct static budget
- Available static
- Blower rated external static
- = Available for the duct
This is the duct side only. The blower also has to push through the filter, the coil, and the grilles — check the total against the blower table in the install manual.
Coil, filter, register, grille and damper losses are already deducted from the blower's rating above — the duct budget is what's left. Verify the blower-table numbers against the install manual.
Equal-friction sizing per the ACCA Manual D® method (not an ACCA-certified product), galvanized round duct. Estimating aid — not an engineered mechanical drawing. Confirm against the manufacturer's install manual and your local code before you cut metal.