Project
Set your design conditions once. A climate preset fills in outdoor temps and a quick-estimate factor — adjust anything to match your job.
Saved projects
Load mode
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Total cooling BTU/h
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Total heating BTU/h
Equipment selection
Tonnage comes from the cooling load. Don't oversize — bigger isn't better (short-cycling, poor dehumidification).
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Calculated tons
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Suggested nominal
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Cooling load BTU/h
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Heating load BTU/h
Airflow
Total CFM = tonnage × CFM/ton (~400 typical; 350 humid, up to 450 heat pumps). Per-room CFM is split by each room's share of the cooling load, rounded to the nearest 5. Override any room's CFM on the Ducts tab.
Blower table helper
Optional — enter a few CFM / external-static points from your unit's blower performance table (for the speed tap you'll run). The app interpolates the static at your design airflow, then you can drop it into the rated-static field below.
CFM
Static (in.wg)
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Static at design CFM (in.wg)
Available static pressure
Friction rate isn't a guess. Start with the blower's rated external static, then subtract the device losses that aren't duct friction. What's left is what your ductwork has to spend.
Component losses — these are the fixed equipment pressure drops only (coil, filter, registers/grilles, dampers, etc.), not straight duct or sheet-metal fittings. Duct length and fittings (elbows, takeoffs, boots) belong in the Worst runs section below. Uncheck any that don't apply, edit values to match your equipment:
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Available static pressure (in.wg)
Runs — find the worst case
Build your longest supply run and your longest return run. Each fitting adds its equivalent length. The run with the highest total effective length (TEL) on each side drives the design.
Auto-pull builds a supply run for every room (plus a return) with a default takeoff + boot. Then just edit the measured length on each — the longest becomes your worst case.
Design friction rate
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Worst supply TEL (ft)
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Worst return TEL (ft)
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Total TEL (ft)
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Design friction rate (in.wg/100ft)
Friction rate = (ASP × 100) ÷ Total TEL, where Total TEL = worst supply run + worst return run. This is your design rate — choose whether duct sizing uses it or a manual rate on the Ducts tab. Fitting equivalent lengths are typical residential defaults — verify against your Manual D fitting tables; they vary with fitting type and air velocity.
Friction rate for sizing
Size ducts with:
Trunk & main sizing
| Run | CFM | Size | Vel |
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Supply branches
| Room | CFM | Size | Vel | Register |
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Registers & grilles (Manual T)
Terminals are sized so face velocity stays low enough to be quiet. Pick the velocity targets and free-area ratio for the diffuser line you install, then the table above and the return below size to match each room's CFM.
| Terminal | CFM | Size | Face vel |
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Supply target ≤ ~500–600 fpm for quiet throw; return grilles ≤ ~350–400 fpm. Free-area ratio is typically 0.70–0.80 for stamped faces, higher for bar grilles — check the cut sheet.
Summary
| Room | Area | Cool | CFM | Duct | Reg |
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Export
Export on one device, then Import the .json on another to move a job (phone ↔ PC). Importing replaces the current open project.
About these numbers
Quick mode is a square-foot rule-of-thumb for fast field estimates. Detailed mode is a simplified
Manual J-style component calc (walls, windows, ceiling, infiltration). Both are estimates — for permits
or final equipment selection, confirm with full ACCA Manual J / S / D software. Duct sizes use the
equal-friction method matched to the standard ASHRAE friction chart.