Quick answer: A refrigerated air dryer cools compressed air to roughly 35–40°F (about 2–4°C) pressure dew point, which is enough for most workshops, air tools and general painting. A desiccant dryer removes much more moisture, typically down to −40°F (−40°C) or lower, and is used where air lines run through freezing areas or the process needs extremely dry air.
Why compressed air needs drying
Air drawn into a compressor contains water vapor. When the air is compressed, that vapor is concentrated, and as the air cools in tanks and pipes it condenses into liquid water. That water rusts pipes, washes lubricant out of air tools, causes paint defects and can freeze in lines. A dryer removes vapor before it can condense downstream.
Understanding pressure dew point
Pressure dew point is the temperature at which water starts to condense from the compressed air at line pressure. If your air has a pressure dew point of 38°F and your pipes never get colder than that, no liquid water will form in them. The lower the dew point, the drier the air.
Refrigerated vs desiccant compared
| Factor | Refrigerated dryer | Desiccant dryer |
|---|---|---|
| Typical dew point | About 35–40°F (2–4°C) | About −40°F (−40°C) or lower |
| Purchase cost | Lower | Higher |
| Running cost | Electricity for refrigeration | Purge air or heaters for regeneration |
| Freezing environments | Not suitable below its dew point | Suitable |
| Typical use | Workshops, garages, general manufacturing | Outdoor lines in winter, instrumentation, sensitive processes |
Types of refrigerated dryer
- Non-cycling: The refrigeration system runs continuously. They are simple and hold a steady dew point and are common in small and medium systems.
- Cycling: They use a thermal mass and switch the refrigeration on and off with demand, saving energy at partial load.
- High-temperature (high-inlet): Built to accept hotter air, such as from a piston compressor without an aftercooler, and cool it before drying.
Our compressed air dryer range includes non-cycling and high-temperature refrigerated models from about 25 CFM to over 350 CFM.
How to size a dryer
Start with the compressor’s delivered CFM. The dryer’s rated flow must be at least that figure under your conditions. Ratings are published at standard conditions, commonly 100°F inlet air, 100°F ambient and 100 PSI. If your compressor room runs hotter, your inlet air is hotter, or your pressure is lower, the dryer’s real capacity drops. Manufacturers publish correction factors for this, so check them in the product documentation. When in doubt, choose the next size up.
Installation tips
- Install a pre-filter ahead of the dryer to keep oil and particles out of the heat exchanger.
- Fit an automatic drain on the dryer’s separator and on the receiver tank.
- Place the dryer in a ventilated area; refrigerated dryers reject heat into the room.
- Add a bypass with valves so you can service the dryer without shutting down the air system.
For the rest of the moisture control system, see air compressors for painting.
Frequently asked questions
Can a refrigerated dryer be used outdoors?
Only if it is designed for it and temperatures stay within its operating range. Freezing conditions call for a desiccant dryer or protected installation.
Do I need a dryer for a small garage compressor?
For occasional tire inflation, often not. For daily air tool use, painting or long pipe runs, a dryer prevents water problems.
Where should the dryer go: before or after the tank?
A common layout is compressor, receiver tank, filter, then dryer. The tank lets air cool and drops out some liquid first. Follow the dryer manufacturer’s recommendation.
Send us your compressor model, CFM and room conditions and we will help you pick a dryer size.