Air Dryer Sizing Calculator #

Q: What size air dryer do I need for a 215 SCFM compressor?

At reference conditions (38°C inlet, 38°C ambient, 7 bar gauge) with a 15% margin, Required ≈ 215 × 1.15 = 247 SCFM rated dryer capacity. Hotter inlet air increases the required rating; cooler ambient decreases it.

Q: When should I choose a refrigerated vs desiccant air dryer?

For pressure dew point around +3°C to +10°C (ISO water Class 4–6), a refrigerated dryer is usually enough. For PDP at or below −20°C (Class 1–3), use a desiccant dryer. Desiccant units typically consume about 10–15% of process air for regeneration.

Size a compressed air dryer from compressor SCFM and target pressure dew point (PDP). Applies typical inlet, ambient, and pressure correction factors, then recommends refrigerated vs desiccant type. For compressor FAD first, use the air compressor sizing calculator.

Dryer Inputs

Units

Compressor Flow (SCFM / FAD)

Target Pressure Dew Point (°C)ISO water Class 4 ≈ +3°C; Class 2 ≈ −40°C

Dryer Type

Advanced calculator

Correction factors use typical manufacturer reference conditions: 38°C inlet, 38°C ambient, 7 bar(g) / 100 PSIG.

Dryer Inlet Temperature (°C)Aftercooler outlet / dryer inlet

Site Ambient Temperature (°C)

Working Pressure (PSIG)

Safety Margin (%)Typical 10–15% for peaks / growth

About this calculator

Required dryer rating uses Required SCFM = Compressor SCFM ÷ (C_inlet × C_ambient × C_pressure) × (1 + margin). Factors are typical planning values—confirm the OEM capacity table for the dryer you buy. Compare technologies in the refrigerated vs desiccant air dryer guide. Browse all pneumatic calculators.

Results

Recommended Dryer Rating

247.3 SCFM

Recommended Type

Refrigerated (auto)

ISO 8573 Water Class

Class 4 (≤ +3°C PDP)

Correction Factors

Cᵢ=1.00 × Cₐ=1.00 × Cₚ=1.00 = 1.000 · margin 15%

Continue Your Calculation

After dryer rated SCFM and type, size distribution piping and quantify leak waste on the dry side.

Pipe sizing →

Quick Reference: Typical Correction Factors #

Planning factors at common conditions (reference ≈ 38°C / 7 bar(g)). Always confirm the dryer OEM table.

Condition	Value	Typical factor	Effect
Inlet temperature	38°C	1.00	Reference
Inlet temperature	49°C	≈0.82	Needs larger rated dryer
Ambient	21°C	≈1.15	Cooler site → more capacity
Pressure	7 bar(g)	1.00	Reference
Safety margin	10–15%	×1.10–1.15	Peaks / growth

Formulas and Method #

Required dryer rated capacity

Required_rated_SCFM = Compressor_SCFM ÷ (C_inlet × C_ambient × C_pressure) × (1 + margin/100)

Manufacturers rate dryers at a reference inlet temperature, ambient, and pressure. When your site is harsher (hot inlet, hot ambient, lower pressure), the combined factor drops below 1.0 and you need a larger nameplate rating for the same compressor flow.

ISO 8573-1 water class vs PDP

Class 4 ≤ +3°C · Class 3 ≤ −20°C · Class 2 ≤ −40°C · Class 1 ≤ −70°C (pressure dew point)

Refrigerated dryers typically target Class 4–6. Desiccant dryers target Class 1–3. This page maps PDP to water class only—particles and oil are separate ISO digits.

Assumptions and Limitations

Correction factors are typical planning values, not a single OEM catalog. Steady flow assumed; intermittent peaks may need extra margin. Desiccant regeneration often uses 10–15% of process air. Verify aftercooler performance, condensate drains, and filter ΔP with the equipment supplier. Not a code-final design.

Refrigerated vs desiccant (quick chart) #

Type	Typical PDP	ISO water	Common uses
Refrigerated	+3°C to +10°C	Class 4–6	General pneumatics, blow-off
Desiccant	−20°C to −70°C	Class 1–3	Paint, food packaging, outdoor lines

Worked example: 215 SCFM @ 38°C inlet / 38°C ambient / 7 bar(g), PDP +3°C, 15% margin → 247 SCFM refrigerated (Class 4). Same flow with inlet 49°C → about 301 SCFM rated.

Frequently Asked Questions #

How do I calculate the right size for a compressed air dryer?

Divide compressor SCFM by the combined correction factor (inlet × ambient × pressure), then apply a 10–15% margin. This calculator shows each factor so you can see why a hotter inlet needs a larger dryer rating.

What size air dryer do I need for a 215 SCFM compressor?

At reference 38°C / 7 bar(g) with 15% margin, you need about 247 SCFM of rated dryer capacity for a +3°C PDP refrigerated dryer. Change inlet or ambient to see the rating move.

When should I choose a refrigerated vs desiccant air dryer?

Use refrigerated for PDP near +3°C to +10°C (ISO water Class 4–6). Use desiccant for PDP ≤ −20°C (Class 1–3). Desiccant systems usually purge 10–15% of air for regeneration—leave compressor headroom.