Formula
Actual SCFM = Nameplate × F(inlet T) × F(inlet P) × F(ambient T)Nameplate SCFM is rated at 100°F inlet air, 100 psig, 100°F ambient. Hot/low-pressure conditions cut real capacity sharply.
Corrected capacity
166scfm
Combined factor 0.83 × nameplate
Correction factors used
Inlet temp factor0.85
Inlet pressure factor0.96
Ambient temp factor1.02
Capacity loss > 15%. If this dryer follows a compressor at full load, expect wet air downstream. Add headroom or improve cooling.
Field notes
- Inlet temp is the air leaving the aftercooler — not shop ambient.
- Every 5°F above 100°F inlet drops capacity ~10–15%.
- At 80 psig dryers run at ~92% of 100 psig capacity.
- Hot mechanical rooms throttle the condenser — fix airflow first.
How to use this calculator
Apply inlet temperature, ambient and pressure correction factors to a dryer's rated capacity.
- Enter the dryer's nameplate rated flow.
- Enter actual inlet air temperature, ambient temperature and operating pressure.
- Read the corrected capacity after all derating factors.
- Verify the corrected capacity still exceeds peak system demand.
Frequently asked questions
- Why must dryer capacity be derated?
- Ratings are published at standard conditions (typically 100 psig, 100 °F inlet, 100 °F ambient). Hotter inlet air, hotter ambient or lower pressure all cut real capacity, sometimes by 30% or more.
- How much does low pressure hurt dryer capacity?
- Lower pressure means higher actual volume for the same mass, so a dryer at 80 psig handles noticeably less SCFM than the same unit at 100 psig.
- Should the dryer be sized on peak or average flow?
- Size on peak flow at the worst-case summer inlet and ambient temperatures, not on average demand.