The Castair RD25-6K is a refrigerated compressed air dryer rated at 25 CFM at a 37°F pressure dew point. It is designed for small to mid-size shops running a single compressor in the 5–10 HP range — paint booths, body shops, production lines, or any shop where moisture-sensitive tools and equipment require consistently dry air. If you are dealing with water in your air lines, spitting from spray guns, or premature failure of pneumatic tools, this dryer solves the problem permanently.
Refrigerated dryers are the industry standard for removing moisture from compressed air. The RD25-6K uses environmentally friendly refrigerant (R134a or R407c) to chill the compressed air to a 37°F dew point. At that temperature, water vapor condenses into liquid droplets and gets ejected through the automatic drain — before it ever reaches your tools, paint guns, or pneumatic cylinders.
How It Works
- Refrigeration cycle: Compressed air passes through a stainless steel heat exchanger. Freon refrigerant absorbs the heat, dropping the air temperature and condensing the moisture out of suspension.
- Dual-function heat exchanger: The single-body design pre-cools incoming hot air with outgoing cold air, improving efficiency and reducing refrigerant load.
- Automatic drain: The onboard drain only cycles when water is present — it does not waste compressed air by draining on a fixed timer. Less compressed air lost means lower operating costs.
- Dew point indicator: Simple visual indicator confirms the dryer is maintaining proper dew point without requiring any programming or computer logic.
Key Features
- Rated capacity: 25 CFM at 37°F dew point (28 CFM at 50°F dew point)
- Inlet/outlet connections: 3/4" NPT — matches directly to most single-stage and two-stage piston compressors in the 5–10 HP class
- Power supply: 115V / 1-phase / 60Hz with 9-foot three-prong power cord — plugs into standard shop outlet, no special wiring
- Current draw: 3.0 amps — minimal electrical load
- Refrigerant: R134a / R407c (environmentally friendly, not R22)
- Maximum inlet pressure: 232 psig — well above standard shop compressor pressures
- Heat exchanger material: Stainless steel for corrosion resistance and long service life
- Quick connect: Refrigerant recharge port for field service without disassembly
- Certifications: UL listed
- Weight: 57 lbs
- Dimensions (W×D×H): 10.6" × 17.9" × 19.6"
Why Moisture in Compressed Air Is a Real Cost Problem
Untreated compressed air carries water vapor — the amount depends on ambient humidity and the temperature the air is compressed to. As the air cools downstream, that vapor condenses into liquid water inside your lines, tanks, and tools. The results are visible: rust in air lines, spitting spray guns, air tools that fail early, and corrosion in pneumatic cylinders and solenoids. According to Castair, adding a properly sized refrigerated dryer reduces overall air system maintenance costs and downtime by 15–25%. That is a real number across a busy shop.
What's in the Box
- Castair RD25-6K refrigerated air dryer unit
- 9-foot three-prong 115V power cord (pre-installed)
- Refrigerant pre-charged at the factory (R134a/R407c)
- Inlet/outlet 3/4" NPT connections
Note: A properly sized pre-filter is required for warranty. The Castair C-FS34 or C-FM14 particulate filter is recommended upstream of the dryer. Vibration pads and flex hose are recommended for installation.
Available Configurations / Upgrade Path
Castair offers a complete lineup of refrigerated dryers. All models run on 115V/1-phase/60Hz power and share the same refrigerant technology and automatic drain design. Here is where the RD25-6K fits:
- RD25-6K — 25 CFM @ 37°F: This unit. For compressors in the 5–7.5 HP range producing up to 25 CFM. Single shop or single bay applications. 3/4" NPT connections, 57 lbs, 10.6" × 17.9" × 19.6".
- RD59-11K — 59 CFM @ 37°F: Next step up. For compressors in the 10–15 HP range. Same 3/4" NPT connections, 73 lbs, slightly larger footprint.
- RD71-15K — 71 CFM @ 37°F: For 15–20 HP compressors. Upgrades to 1" NPT connections, 110 lbs.
- RD113-60K — 107 CFM @ 37°F: For 20–25 HP compressors. 1" NPT, 119 lbs.
- RD161-37K — 161 CFM @ 37°F: For larger systems. 1-1/2" NPT, 137 lbs.
- Larger sizes available — call for pricing.
When Does a Shop Need This vs. Stepping Up or Down
The RD25-6K is right for your shop if:
- You have a compressor producing 25 CFM or less (typically 5–7.5 HP)
- You have a single-bay paint booth, a body shop with one spray gun running at a time, or a small production line
- You need 115V single-phase power — no three-phase electrical available
- Space is limited — this is a compact unit at under 11" wide
Step up to the RD59-11K if:
- Your compressor is 10 HP or larger and produces more than 25 CFM peak demand
- You are running multiple tools simultaneously from the same compressor
Capacity note: Dryer capacity ratings are based on 100°F inlet air temperature, 100°F ambient temperature, and 100 PSI operating pressure. If your air is hotter than 100°F at the dryer inlet (common with compressors without aftercoolers), actual capacity is reduced. At 150°F inlet air temperature, effective capacity drops to 55% of rated — meaning this dryer would handle approximately 14 CFM, not 25. An aftercooler upstream of the dryer is strongly recommended in high-temperature installations.
Installation Options
Castair offers installation kits for mounting the dryer directly on the compressor:
- #DM75: Mount kit for RD59-11K or smaller — includes 3/4" NPT 3-ball valve bypass, metal flex hose, and vibration pads. Allows the dryer to be bypassed for service without shutting down the compressor.
Technical Specifications
- Model: RD25-6K
- CFM @ 37°F dew point: 25
- CFM @ 50°F dew point: 28
- Inlet/Outlet Connection: 3/4" NPT
- Voltage / Phase / Hz: 115V / 1-phase / 60Hz
- Amperage: 3.0 A
- Refrigerant: R134a / R407c
- Maximum Inlet Pressure: 232 PSIG
- Pressure Dew Point: 37°F
- Heat Exchanger: Stainless steel, dual-function single body
- Drain Type: Automatic, cycles on demand
- Power Cord: 9 ft, three-prong 115V plug
- Weight: 57 lbs
- Dimensions (W×D×H): 10.6" × 17.9" × 19.6"
- Certifications: UL Listed
- Capacity Rating Basis: 100°F inlet air, 100°F ambient, 100 PSI
Why Buy From Air Compressor Factory Direct?
We have been selling and supporting compressed air equipment since 2016 — not as a general industrial distributor, but as a specialist. When you call us, you talk to someone who can confirm whether the RD25-6K is right for your compressor or whether you need to step up to the RD59-11K. We offer free shipping on qualifying orders, free pre-sale technical support, and the full Castair manufacturer warranty. If you need installation guidance, filter sizing help, or want to talk through the full air treatment system for your shop, we are here for that conversation.
Call 866-217-0063 for quick answers and help!
