Equipment Protection
Reduce Rust and Corrosion
Removing moisture helps protect air receivers, piping, valves, cylinders and pneumatic equipment from internal corrosion.
Compressed Air Treatment Buyer's Guide
How to Choose an Air Dryer | Complete Buyer's Guide
Choosing the right compressed air dryer starts with four questions: how much airflow your system produces, your operating conditions, the pressure dew point your process requires, and what happens if moisture reaches the point of use.
This guide compares refrigerated and desiccant air dryers, explains sizing and pressure dew point, and helps you build a complete air treatment system around your compressor.
Quick Answer: Which Air Dryer Should You Choose?
Choose a refrigerated air dryer for most indoor industrial and shop applications that need reliable moisture removal and a pressure dew point near 38°F to 45°F.
Choose a desiccant air dryer when the air lines may be exposed to freezing temperatures or the process requires a much lower pressure dew point, commonly around -40°F.
Then size the dryer for your actual system airflow and correct for inlet temperature, ambient temperature, operating pressure, duty cycle and future demand. The dryer's rated CFM must meet or exceed the corrected airflow requirement—not only the compressor's nameplate horsepower.
General manufacturing, pneumatic tools, automotive service or indoor shop air?
Start with a refrigerated dryer.
Air lines, valves or instruments exposed to temperatures below freezing?
Use a desiccant dryer or another system designed for the required low dew point.
Instrumentation, sensitive process air or a specified -40°F pressure dew point?
Choose a desiccant dryer.
Food, medical, pharmaceutical or other regulated application?
Design to the applicable air-quality standard; a dryer alone may not provide the required air purity.
Why Does Compressed Air Need to Be Dried?
Atmospheric air always contains water vapor. A compressor pulls that air in, concentrates it and raises its temperature. As the compressed air cools in the aftercooler, receiver tank and piping, water vapor condenses into liquid water.
Without proper air treatment, that moisture can move downstream and contribute to corrosion, frozen controls, damaged pneumatic tools, contaminated finishes, inconsistent processes and unplanned downtime.
Step 1Humid ambient air enters the compressor
Step 2Compression raises pressure and temperature
Step 3Hot compressed air holds water vapor
Step 4Air cools in the system
Step 5Water vapor condenses
Step 6Dryer and drains remove moisture
Process Reliability
Improve Product Quality
Dry air helps reduce water contamination in painting, packaging, instrumentation and other moisture-sensitive processes.
Winter Operation
Help Prevent Freeze-Ups
When compressed air piping is exposed to low temperatures, a sufficiently low pressure dew point helps prevent condensed water from freezing.
What Are the Main Types of Compressed Air Dryers?
The two most common industrial choices are refrigerated dryers and desiccant dryers. Refrigerated dryers cool the air so moisture condenses and can be removed. Desiccant dryers adsorb water vapor onto a drying material and regenerate that material in alternating towers.
Compressed Air Dryer Types Compared
| Dryer Type | Typical Pressure Dew Point | Best For | Primary Consideration |
|---|---|---|---|
| Non-Cycling Refrigerated | Approximately 38°F to 45°F, depending on model and conditions | General manufacturing, shops, pneumatic tools and most indoor plants | Simple, dependable operation; compressor runs continuously while the dryer is operating |
| Cycling Refrigerated | Usually near the refrigerated-dryer range | Systems with varying air demand where energy savings justify the design | Higher initial complexity but may reduce power use at partial load |
| Heatless Desiccant | Commonly -40°F | Instrument air, outdoor lines and low-dew-point applications | Uses a portion of dried compressed air for regeneration |
| Heated Purge Desiccant | Commonly -40°F | Larger systems requiring lower purge-air consumption | Adds a heater to reduce the amount of compressed purge air |
| Blower Purge Desiccant | Commonly -40°F | Large continuous-duty systems focused on operating efficiency | Uses an external blower and heat for regeneration |
| Membrane | Varies by design, flow and purge setting | Point-of-use, remote or compact applications | Simple and compact, but usually best for lower flow requirements |
When Should You Choose a Refrigerated Air Dryer?
A refrigerated air dryer is the best starting point for most indoor compressed air systems. It cools the compressed air, condenses water vapor, separates the liquid and then reheats the dry air before it leaves the dryer.
Atlas Copco FX dryers are designed for pressure dew points as low as approximately 37°F, while Quincy refrigerated dryer literature describes operation near 39°F to 45°F depending on the series and rating conditions.
Shop all refrigerated air dryers or narrow the selection to Atlas Copco refrigerated dryers and Quincy refrigerated dryers.
Best Fit
Choose Refrigerated When:
- The air system is located indoors and remains above freezing
- The application is general manufacturing or shop air
- Pneumatic tools, cylinders and standard controls are the primary loads
- A pressure dew point near 38°F to 45°F is sufficient
- Low maintenance and straightforward operation are priorities
Watch For
Refrigerated Dryers May Not Be Enough When:
- Piping or equipment will be exposed to freezing temperatures
- The process specification requires a -40°F pressure dew point
- The application requires exceptionally dry instrument air
- Air-purity standards require additional filtration or purification
- Inlet air temperature exceeds the dryer's rated conditions
Atlas Copco
FX Refrigerated Air Dryers
The Atlas Copco FX range includes refrigerated dryers for a broad range of industrial airflow requirements. Available literature lists models from approximately 14 to 2,516 CFM and pressure dew points as low as about 37°F.
Quincy
QPNC and COOL Refrigerated Air Dryers
Quincy non-cycling refrigerated dryers use heat exchangers, moisture separation and condensate drains to remove liquid water. Quincy QPNC literature covers models from approximately 13 to 3,000 CFM.
When Should You Choose a Desiccant Air Dryer?
A desiccant dryer is used when the required pressure dew point is much lower than a refrigerated dryer can provide. Wet compressed air passes through a tower filled with adsorbent material. Moisture adheres to the desiccant while a second tower is regenerated. The towers switch so the process can continue.
Heatless, heated purge and blower purge designs use different regeneration methods, but industrial desiccant systems commonly target a pressure dew point around -40°F.
Shop all desiccant air dryers, browse replacement desiccants, or view Atlas Copco desiccant dryers and Quincy desiccant dryers.
Heatless
Heatless Desiccant Dryers
Heatless dryers use a portion of dry compressed air to regenerate the off-line tower. They are mechanically straightforward but consume purge air.
Heated Purge
Heated Desiccant Dryers
Heated purge dryers add heat during regeneration, which can reduce the amount of dried compressed air required for purge.
Blower Purge
Blower Purge Dryers
Blower purge systems use ambient air moved by a blower and heated for regeneration, making them attractive for larger continuous-duty systems.
Protect the desiccant: Oil and liquid water can shorten desiccant life and reduce dryer performance. Install the correct upstream separator and prefilters, and use an after-filter to capture desiccant dust before air enters the distribution system.
Replacement Media
Activated Alumina Desiccant
Browse activated alumina media in several bead sizes and package quantities for supported desiccant dryer applications.
Replacement Media
1/8-Inch Activated Alumina
Replacement activated alumina desiccant for compatible dryer vessels and service requirements.
Replacement Media
4A Molecular Sieve
Molecular sieve media for compatible applications requiring strong water-vapor adsorption performance.
Refrigerated vs. Desiccant Air Dryers
The best dryer is not determined by which technology is more advanced. It is determined by the air quality your process requires and the operating environment your compressed air system must handle.
Refrigerated and Desiccant Air Dryer Head-to-Head Comparison
| Selection Factor | Refrigerated Dryer | Desiccant Dryer |
|---|---|---|
| Typical Pressure Dew Point | Approximately 38°F to 45°F | Commonly -40°F; lower dew points may be available by design |
| Best Environment | Indoor systems that remain above freezing | Outdoor, cold or moisture-sensitive systems |
| Typical Applications | Manufacturing, automotive, pneumatic tools, general plant air | Instrumentation, low-temperature piping and specified low-dew-point processes |
| Energy Consideration | Refrigeration compressor and fan power | Purge-air loss, heater power or blower power depending on design |
| Maintenance Focus | Condensate drains, heat exchangers, refrigerant circuit and filters | Desiccant condition, valves, purge controls, heaters or blowers and filters |
| Upfront Cost | Generally lower for comparable general-purpose capacity | Generally higher because of the lower dew point and regeneration system |
| Primary Decision | Use when a moderate dew point meets the application | Use when low dew point is required, not simply as an automatic upgrade |
What Is Pressure Dew Point?
Pressure dew point is the temperature at which water vapor begins to condense while the air remains at system pressure. It is one of the most important specifications when selecting an air dryer.
A lower pressure dew point means the compressed air contains less water vapor. The correct target depends on the coldest temperature the air will experience and the moisture sensitivity of the process.
About 38°F to 45°F PDP
General Industrial Air
Common refrigerated-dryer performance for indoor systems, pneumatic tools and many manufacturing processes.
About -40°F PDP
Very Dry Instrument Air
Common desiccant-dryer performance for outdoor piping, instrument air and processes that require very low moisture content.
Application-Specific PDP
Regulated or Critical Processes
Food, medical, pharmaceutical, electronics and other critical processes may require a documented air-quality standard beyond dew point alone.
Do not size a dryer from ambient relative humidity alone. Pressure dew point, inlet temperature, airflow, pressure and dryer correction factors determine whether the unit can deliver the required air quality.
How Do You Size a Compressed Air Dryer?
Start with the maximum actual airflow that can reach the dryer. Then apply the manufacturer's correction factors for operating pressure, compressed-air inlet temperature and ambient temperature. Add capacity for leaks, simultaneous demand and expected system growth.
1. Airflow
Maximum CFM
Use maximum delivered airflow, not average consumption. Include multiple compressors if they can feed the dryer at the same time.
2. Pressure
Operating PSIG
Dryer capacity changes with operating pressure. Lower pressure generally increases the volume the dryer must process.
3. Temperature
Inlet and Ambient Heat
Hotter compressed air carries more water vapor and can substantially reduce a dryer's effective rated capacity.
4. Air Quality
Required Dew Point
The process requirement determines whether refrigerated, desiccant or another treatment method is appropriate.
Air Dryer Sizing Checklist
| Sizing Input | What to Use | Why It Matters |
|---|---|---|
| System Airflow | Maximum expected CFM through the dryer | The dryer must handle peak flow without exceeding its corrected rating. |
| Inlet Pressure | Lowest normal operating pressure | Lower pressure can reduce effective dryer capacity. |
| Inlet Temperature | Highest expected compressed-air temperature entering the dryer | High inlet temperature increases moisture load and may require a high-temperature dryer or additional aftercooling. |
| Ambient Temperature | Highest expected room or outdoor temperature around the dryer | High ambient temperature can reduce refrigerated-dryer performance. |
| Required PDP | The process or environmental dew-point requirement | Determines the dryer technology and expected air quality. |
| Growth Allowance | Commonly 10% to 25%, based on realistic expansion plans | Provides room for future tools or production demand without extreme oversizing. |
Compressed Air Dryer Sizing Tool
Use this tool for a preliminary planning estimate. It recommends a dryer type and a starting nominal CFM based on airflow, operating environment and desired pressure dew point.
Preliminary Dryer Recommendation
Starting nominal capacity —
Recommended technology —
Growth included —
Important: This calculator is a planning aid, not a final equipment selection. The adjustment factors are intentionally conservative and are not a substitute for the correction-factor table published for the exact dryer model. Confirm voltage, maximum pressure, inlet temperature, ambient rating, pressure drop, connection size, drain requirements and dew-point performance before purchase.
Air Dryer Selection by Application
The application determines how damaging moisture would be and how low the pressure dew point should be. The recommendations below are starting points; critical processes should be designed to their governing quality standard.
Compressed Air Dryer Application Guide
| Application | Common Starting Point | Why | Additional Treatment to Consider |
|---|---|---|---|
| Pneumatic Tools | Refrigerated dryer | Helps reduce liquid water, corrosion and tool wear in indoor systems. | Particulate and coalescing filtration; point-of-use regulator. |
| Paint Booth | Refrigerated or desiccant based on finish requirement and climate | Water and oil can contribute to fisheyes, poor adhesion and finish defects. | Coalescing filtration and point-of-use filtration; verify paint-system requirements. |
| Instrumentation and Controls | Often desiccant | Small passages and outdoor controls can be sensitive to moisture and freezing. | High-efficiency prefilter and after-filter; specified dew-point monitoring. |
| Food Packaging | Application-specific | Air that contacts product or packaging may be subject to documented quality requirements. | Appropriate filtration, oil-free strategy where required and validation against applicable standards. |
| Medical or Pharmaceutical | Engineered system—not a dryer-only decision | These applications may require specialized purification, monitoring, redundancy and compliance. | Consult the governing medical, pharmaceutical and facility standards. |
| Outdoor Air Lines | Desiccant when exposed below freezing | The pressure dew point should remain below the coldest expected pipe temperature. | Insulation, drains, low-point management and weather-rated equipment. |
How to Build a Complete Air Treatment System
An air dryer is only one part of moisture and contamination control. A complete system manages bulk liquid water, oil aerosols, solid particles, condensate and point-of-use air quality.
Air Compressor
Aftercooler
Receiver & Drain
Water Separator
Prefilter
Air Dryer
Final Filtration / Point of Use
Bulk Moisture
Water Separators and Drains
Remove condensed liquid before it overloads filters or the dryer. Automatic drains should be installed at appropriate collection points.
Air Quality
Prefilters and After-Filters
Protect refrigerated heat exchangers and desiccant beds from contamination, then capture fine particles or desiccant dust downstream.
Shop compressed air filters or browse all dryers and filters.
Condensate Disposal
Oil-Water Separators
Treat oily compressor condensate before discharge. Select the separator for compressor capacity, operating hours, climate and connected treatment equipment.
Featured Condensate Treatment Products
Shop all separators, oil-water separators, water separators, Atlas Copco separators, or Quincy separators.
Air dryers and drains create condensate that may contain compressor lubricant. These oil-water separators help treat condensate from supported compressed air systems.
Quincy QOCS
QOCS 25 CFM Condensate Purifier
Compact Quincy oil-water separator with a published 10 ppm outlet oil rating.
Quincy QOCS
QOCS 106 CFM Condensate Purifier
Quincy condensate-treatment option for larger supported compressor systems.
Atlas Copco OSC
OSC Clay Oil-Water Separators
Browse individual Atlas Copco OSC clay separator sizes for compatible condensate-management systems.
Need Help Selecting an Air Dryer?
Collect your compressor CFM, operating pressure, dryer inlet temperature, ambient temperature, voltage, required pressure dew point and application. A compressor specialist can help confirm the dryer type, corrected capacity, filtration and condensate-treatment requirements.
Related Air Treatment Resources
These supporting pages are the recommended next pages in the Air Treatment Learning Center. Publish each page at the matching URL so this hub and its supporting content reinforce one another.
Compressed Air Dryer FAQs
What size air dryer do I need?
Choose a dryer whose corrected capacity meets or exceeds the maximum airflow that can pass through it. Apply the manufacturer's correction factors for operating pressure, inlet temperature and ambient temperature, then include a reasonable growth allowance.
Should an air dryer be sized by compressor horsepower?
No. Horsepower can provide a rough estimate, but final dryer selection should be based on maximum delivered CFM, pressure, temperatures, dew-point requirement and the exact dryer's rating conditions.
Can an air dryer be too large?
Moderate oversizing can provide useful capacity, but extreme oversizing may add unnecessary cost and can affect how some dryer designs cycle or control. Size for corrected peak demand plus realistic growth.
What is the difference between refrigerated and desiccant air dryers?
Refrigerated dryers cool compressed air so moisture condenses and can be removed. Desiccant dryers adsorb water vapor onto a drying medium and regenerate that medium in alternating towers. Refrigerated dryers are common for general indoor plant air, while desiccant dryers are used for much lower pressure dew points.
What pressure dew point does a refrigerated dryer provide?
Many industrial refrigerated dryers are rated near 38°F to 45°F pressure dew point under stated conditions. Always verify the exact model's published rating and correction factors.
What pressure dew point does a desiccant dryer provide?
A -40°F pressure dew point is common for industrial desiccant dryers. Some designs may provide other dew points, so selection should be based on the process requirement and published specifications.
Do I need a desiccant dryer for outdoor air lines?
Often, yes, when piping or controls may be exposed below freezing. The required pressure dew point should remain below the coldest expected temperature at which the compressed air will be used.
Where should an air dryer be installed?
A common arrangement places the dryer downstream of the compressor, aftercooler, receiver or bulk-water separation and required prefiltration. Exact placement depends on dryer type, system design and manufacturer instructions.
Does a refrigerated air dryer need a filter?
Many systems benefit from filtration before and after the dryer. The required filter grades depend on compressor type, dryer design and downstream air-quality requirement.
Why does a desiccant dryer need a prefilter and after-filter?
The prefilter helps protect the desiccant from liquid water, oil aerosol and particles. The after-filter helps prevent desiccant dust from entering the downstream air system.
How often should dryer desiccant be replaced?
Replacement timing depends on dryer design, operating hours, inlet contamination, regeneration performance and the manufacturer's maintenance schedule. Monitor dew point and follow the service instructions for the exact dryer.
What happens if the air entering a refrigerated dryer is too hot?
High inlet temperature increases the moisture load and can reduce effective dryer capacity or cause poor dew-point performance. Improve aftercooling or choose a dryer specifically rated for the inlet conditions.
Do I need an oil-water separator with an air dryer?
If an oil-lubricated compressor produces oily condensate, the condensate may require treatment before disposal. An oil-water separator is separate from the air dryer and is selected for the condensate load and applicable discharge requirements.
Is a dryer enough for food, medical or pharmaceutical air?
Not necessarily. These applications may require specific particle, water, oil, microbial, monitoring and validation requirements. Design the complete compressed air system to the applicable standard rather than selecting a dryer alone.