How to Reduce Moisture in Compressed Air Systems

Part of getting a good paint job is having good quality air coming out of your compressed air lines. This is also important when powder coating and media blasting too. Besides the typical separator and desiccant attachments for removing moisture, there are planning, periodic maintenance, and plumbing steps you can take to help with this issue.



Garage layout

Dry air starts in the planning stage of the shop, before you even buy a compressor. You want to plan on the compressor having a good supply of air that is as cool and dry as possible. You may not have much of a choice if you are in a small shop, you can help a compressor stuck in a small damp space like a basement by giving it a vent or window to the outside world. The compressor itself will heat up the air in a small space, and hot air holds more water, making things worse.


Buying a compressor that is big enough will help keep the water dry too. Because hot water carries more moisture, and a smaller compressor will have to run more frequently, which makes it run hotter, a larger unit will provide dryer air. The water vapor will also tend to condense out in the tank as it cools, so a bigger tank is better too. A 2 stage compressor compresses air to a higher pressure, and that makes the air hotter as well, so a single stage one may be better as long as you don’t need the added pressure.

Of course if you have a professional shop you are going to want to invest in an air after-cooler. An after cooler is basically a car radiator that the air gets piped through to chill it, condensing out the water vapor. In fact, if you look online you can actually find plans to turn the top half of your garage beer fridge into an air cooler with not much more than some fittings and copper tubing.


Periodic Maintenance


The biggest periodic maintenance task to do regularly is drain the compressor tank. There is only so much water that can sit in the bottom of the tank without being fed through the lines and into your tools and spray guns. If you don’t have a daily, weekly or monthly draining schedule, you at least want to drain the tank the night before doing any painting, blasting or powder coating. If you have a typical system, draining the tank also releases all the air, so you need to give your compressor hours to refill the air supply and cool off before staring.

The other periodic maintenance item is a check of all the filers, water separators, and air dryers in your system. What is involved here depends on what sort of systems you use. Desiccant dryers often have a color change feature that lets you know when they need to be replaced. Separators often just need to be drained periodically. Check the manual or website of the filter to see how you determine when they need to be cleaned or changed.



tubing kit

Plumbing may be the easiest and lowest cost way to reduce the amount of water in your system. Kevin Tetz himself in an Eastwood how-to seminar revealed this tip: Run at least 50ft of line between your compressor and your spray gun. Now you may read that and think you’ll have to go spray in your neighbor’s driveway to get 50ft away, but that is not the case. The recommended set up is to run hard lines vertically along the wall, up and down, 2 or 3 times, with a drain valve at the bottom of each. Water droplets will be knocked out of the airstream each time it has to turn a corner. The added length gives the air room to cool down from the compressing it got, which condenses out more water. Finally, the up and down nature of the pipes gets gravity on your side to collect the water someplace safe away from the paint.


filter regulator

The other plumbing that will help with clean dry air is a wall mounted dryer/filter/regulator combo just before your flexible rubber air hose. Eastwood carries a number of different systems at a number of different price points, but even if you spend a couple of hundred dollars to ensure clean dry air, it pays for itself the with the first fish eye, or orange peel it prevents from happening. Plumbing these right at the end of the line allows them to work longer before needing to be cleaned/replaced, because the 50ft delivers cleaner dryer air.

Eastwood offers all of these air management Items in a complete kit, the RapidAir Complete Garage kit includes 100′ of hose, valves, connectors, hose mounting clamps and a hose cutter. Everything you’ll need to set up a garage air system, if more hose and connectors are needed they can be purchased separately


disposable filter

Lastly, you’ll want to attach a disposable filter or dryer directly to the gun. This final step is just added protection, and will also eliminate any dirt or moisture from the rubber line getting into the paint. Both the desiccant type and the whirlwind type clean and dry the air and cost about what you would spend on lunch or beer for a weekend project.


  1. Great info here. My shop should be up by the end of next month (I hope) and this is perfect. It’s a very small shop, but should do just fine.
    Thx for the great stuff.

  2. WHAT???
    Buying a compressor that is big enough will help keep the water dry too. Because hot water carries more moisture, and a smaller compressor will have to run more frequently, which makes it run hotter, a larger unit will provide dryer air.

  3. I would like your opinion on using your air compressor for using the SAS breathable air system. Is it neccesary to use their CO2 monitor while breathing air from compressor.

  4. Hi,
    Do you have a water filter/drier for a
    20 gallon air tank ?
    I am looking for one that I can attach a 30 foot air hose to . I do not have a garage and do work outside.Any help appreciated.
    Thanks, Ron

  5. Drawing should show drops to continue below air outlets to collect moisture and debris(especially on a hard pipe system with rust and pipe scale) with a drain valve below.Also the determining factor on selection of an air compressor is scfm not pressure.

  6. ALL compressed air piping drops should be taken from the TOP of the distribution piping. This is another way to minimize the amount of condensation reaching your paint gun.

    I recommend the use of type L copper or stainless steel for the distribution piping.

  7. Re-plumb your compressor wing drain with an elbow and ball valve of the right size coming out of the end of the tank.
    This will make draining your air compressor much easier, and prompt you to do it more often.
    Besides you don’t have to deal w/ the ” wing valves” sticking shut on you.
    I learned this from my own experience.

  8. Read this article with interest. I have been considering a method of cooling/drying air for a few years. The cause of this is exactly as you described but for a large media unit. What do you think of using modified refrigerant coolers off the backs of refrigerators & freezers? The cfm looks adequate, fittings will need to be modified. They are obviously designed with the curves, angles, and have fins, what do you think? Yes, I am one of your consumers. Thanks Max Wilkerson

  9. Each “horizontal ” section of the air line needs to slope downward away from the compressor. This allows the moisture to gravity -flow to the low drain points in the same direction as the air flow

  10. For years, I address compressor moisture by simply cracking ever so slightly the drain pet cock. This is an automatic, constant way of removibg moisture. In addition, tilting a horizontal compressor tank flows the water towards the petcock.

  11. We tried that and it exploded and sent shards of plastic shrapnel all over the shop!

  12. Never use your home system for breathable air. Systems designed for breathable are have much more filtration and oil removal components. Air from your home system could be very harmful to breath.

  13. Is that blue piping PEX ??? Also there was a question about using #80 PVC for a 120 lb system. I have read where PVC is a NO-NO.
    But others have used it with NO problems at
    135 lb systems.

  14. The piping you see is meant for high pressure compressed air systems. We do not recommend normal PVC you get at a home supply store.

  15. I have a personal shop I’m going to be plumbing, I have purchased a large stand up Compressor and a rapid air kit. Along with normal air tools I will be using an Eastwood plasma cutter and in the future some painting, which filter/dryer do you recommend, and can it be bypassed when only using air tools to prolong the dryer media? I’m also using an airhose reel, thank you, George

  16. I tried all kind of things filters/traps lines that ran down hill to such but I found out a second receiver tank would cool air and I would tap air from it NEVER Had a problem again!

  17. Another idea is what we use in our shop. I purchased a dehumidifier several years ago and we can keep the relative humidity in the shop at about 40%. The shop is pretty tight so that is not a problem. Thus when the compressors run their air intake is already pretty dry.

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