Diffuser Throw Calculator
Air throw distance and spacing for diffusers.
Enter your values
ⓘ Live results
Results
- Throw distance
- 12.7 ft
- Target throw (75% of distance)
- 9 ft
- Fit
- Good coverage
- Suggested spacing
- 17.8 ft
- Airflow
- 200 CFM
Quick answer
Diffuser throw is the distance air travels before slowing to 50 FPM, and it should reach roughly three-quarters of the way to the wall.
throw ≈ K x sqrt(CFM) for the diffuser type
How to use the Diffuser Throw Calculator
- 1Enter the airflow each diffuser handles and pick the type.
- 2Compare the throw to about three-quarters of the distance to the opposite wall.
- 3Space diffusers at roughly 1.4 times the throw for even coverage.
Worked example
Using the values the calculator loads with:
Inputs
- Airflow per diffuser200 CFM
- Diffuser type4-way ceiling
- Distance to wall12 ft
Results
- Throw distance12.7 ft
- Target throw (75% of distance)9 ft
- FitGood coverage
- Suggested spacing17.8 ft
- Airflow200 CFM
Frequently asked questions
What happens with short throw?
Air dumps straight down, creating cold spots under the diffuser and stagnant zones at the perimeter.
Heating vs cooling?
Warm supply air is buoyant and throws less, so perimeter throw matters most in heating.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.