Free duct airflow calculator
Duct CFM Airflow Calculator
Enter the system size and design target to get total supply airflow, then optionally a room's floor area to see its proportional share of that air.
Quick answer: How many CFM should my AC deliver? A 3-ton system moving the typical design target of 400 CFM per ton delivers about 1,200 CFM of supply air. A 180 sq ft room in a 1,800 sq ft home receives roughly 120 CFM — its proportional share by floor area.
How many CFM should my AC deliver?
How this calculator works
Total CFM = tons × CFM per ton (350, 400, or 450). Room share = total CFM × room area ÷ total home area. The 400 CFM per ton figure is a long-standing design convention; manufacturer data may specify 350–450 CFM per ton for specific equipment.
Pinellas County context
Weak airflow in one room is rarely solved by closing other registers — that raises static pressure and can freeze the coil. If a room consistently runs hot through a Pinellas County summer, have the ducts and static pressure measured before adjusting anything.
Frequently asked questions
Is 400 CFM per ton always the right target?
It is the most common design target in Florida, but it is not a constant. Manufacturers may specify 350 CFM per ton where humidity removal matters most (lower airflow removes more moisture per cycle) or 450 CFM per ton for drier sensible cooling. Your equipment's data plate wins over any rule of thumb.
How do I calculate CFM for one room?
The calculator's room-share method allocates total system airflow in proportion to floor area. Precise duct design allocates by each room's Manual J load instead — a sunny west-facing room needs more than its floor-area share; an interior bathroom needs less. Treat the room figure as a sanity check, not a duct sizing spec.
Can a dirty filter change CFM?
Yes, significantly. A clogged filter raises static pressure, cuts airflow across the coil, and can drop delivered CFM enough to freeze the coil or trip the system on a limit switch. Checking the filter monthly during cooling season is the cheapest airflow protection there is.
Does duct cleaning increase airflow?
Only when debris blockage is the restriction. Cleaning cannot fix undersized or crushed ducts, closed dampers, or leaky connections — and those cause most real airflow losses. A Hales AC technician measures static pressure and delivered CFM to find which one you have.