Air Compressor Guide

This isn't a formal "product review" in that we're not reviewing a specific product but instead a comparing the pros and cons of the different types of air compressors available to the average guy (or gal) for the workshop, regardless of brand or model.

I've been asked about what size and style of air compressor to buy for a home workshop. I'm no expert, but I've had some experience with them over the past 18 years. First, the bottom line:

My Top Choice - 80 Gallon Two-stage:
If you're bucks up, my first choice would be to get a 80-gallon, 2-stage compressor. Tons of air and the 90psi+ pressure in the tank lasts forever because the pump will pressurize it to 175 psi, generally. However, you're looking at a minimum of $750 for a "cheap" brand and a grand or more for a "good" brand, 2-stage compressor.

My Second Choice - 60 Gallon Single-stage:
Second choice, and the one I recommend for most hobbyists, is a 220V, 60-gallon, single-stage, belt-driven compressor. You can get one for $400-$600 and they'll do a great job supplying air for your needs. They all run on 220v and usually draw 20 amps or so. Horsepower ratings vary, but those ratings are mostly B.S. as far as I'm concerned, so don't pay too much attention to them. Despite what the manufacturers would have you believe, the main things to look at are air output and tank size; not the horsepower of the motor. CFM at a certain pressure is what powers the air tools, and the tank size represents a compressor's "reserve capacity", so to speak. If you have 1000 gallons at 135psi it's going to take a long, long time for that pressure to drop below your air tool's operating pressure, which means the compressor runs less frequently. If you only have a two-gallon tank, that compressor is going to be stopping and starting every minute or less which is hard on the compressor and is rather annoying. Those are extreme examples, of course, I just used them to illustrate the point. Get the biggest tank you can find, afford, and have room for.

My Third Choice - 110V Portable:
Third choice is a 25-30 gallon portable. Portables are convenient and not too expensive, but they don't have very large tanks and don't generally put out that much air. If you really need portability quite often, get one. But if it's a rare situation that you'll need air on a remote site, it's not worth the sacrifice to get a small compressor.

I've seen some portable units advertised with 5 hp or even more, yet they only put out 5.5 cfm at 90 psi. That's not enough for many air tools and it won't recover the tank pressure very quickly, either. My old Ingersoll-Rand 3.3 hp put out 7.4 cfm at 90 psi and it was good for most things but it could barely keep up with a die grinder and couldn't keep up with a sandblaster or orbital sander. I hate to think how poorly a compressor with only 5.5 or less cfm output would perform.

What I did:
Getting back to my recommended choice behind Door #2:
I did lots and lots of checking around when I was in the market and had decided on a 60-gallon vertical, belt-driven, single-stage compressor. What I found was that the "normal" store-type brands don't put out that much air. I looked at Craftsman, Sanborn, Coleman, Husky, Campbell-Hausfeld, and DeVilbiss and they were all about the same. Who knows, maybe they literally are the same? I wouldn't be surprised if one or two companies made all of them. Anyway, they all put out about 9.0-10.0 cfm at 90 psi. Not much of an improvement over my old portable compressor, other than the increase in tank size.

Then I happened to find an Ingersoll-Rand at a Home Depot that put out 11.3 cfm at 90 psi and 14.7 cfm at 40 psi. Perfect! It cost $450 (about $50 more than the rest) but it's a brand I trust and it had some minor-but-nice features that the others didn't. I've had it since 2001 and have been extremely happy with it....until recently. In the fall of 2007 the pump decided to get abnormally hot, thus melting the air filter's plastic fitting and destroying the filter. I've not yet opened up the pump to see if chunks got inside.

I think the melting of the air filter housing was a result, not a cause, of the problem. The pump shouldn't have been so hot as to melt the plastic, so something else is at fault. I still don't know what it is, though. It still functions, but takes longer to build up pressure than it used to, especially once it gets past about 70psi and it starts to smell funny once it slowly works itself past 85psi or so. I've not convinced myself to stick it out long enough to get past 100psi, if it even would. The surface temperature of the pump exceeds 220F once the pressure builds past 85psi or so. Not good.

Buying a "genuine" I-R pump is prohibitively expensive, as are replacement parts, so I plan to just buy a generic replacement pump from Northern or Harbor Freight for around $100 and hope for the best.

Belt-drive vs. Direct-drive:
Why belt-driven instead of the "convenience" of the oil-free, direct-drive style? Belt-driven compressors are much quieter and the oiling is no big deal. Also, based on the output ratings I've seen, belt-driven compressors put out more air than their direct-drive counterparts. You have to add or change oil once in a while. So what?

Tank Size:
The larger tanks are better because the tank pressure drops at a slower rate than in a smaller tank given the same usage. That's a good thing. Get the largest tank you can.

As for accessories, be sure to get a regulator (most single-stage compressors go to 110-135 psi but most air tools are designed to run at 90 psi), a water trap, and be absolutely sure to use 3/8" line and fittings! I mean the true 3/8" I.D. stuff, not the ones that claim to be 3/8" but their I.D. is barely 1/4". Home Depot is a good source for the larger fittings. I think you can run 100' of hose without much pressure-drop, and with a larger compressor I don't think what little drop there is will be a concern. Quick-release connectors are a must. Also, lever-action ball valves are nice to have at the compressor output and at the tank drain instead of that annoying petcock. I'd be happy to describe in more detail what I'm referring to if you're interested (with pictures), just click the "Contact Bruce" link at the top-left corner of this page.

Decision Time:
If you're in the market for a compressor, I hope you take the information I've given along with some of your own research and make a well-informed decision.

Feedback and questions are always welcome, please click the "Contact" links if you'd like to leave some.

©2015 Bruce Johnson and Craig Watson