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How to Size an Air Compressor Accurately

Air compressors are big machines. Not only do they cost a lot to buy, but they’re also expensive to run. Choosing the right size air compressor is important to ensure you’re making the right investment upfront and running your shop or factory efficiently. An air compressor that’s too small won’t put out enough air, or you’ll run it to death well before the end of its lifespan. An air compressor that’s too large will carry a hefty price tag and will be costly to run. With all of that in mind, how do you size an air compressor accurately?

As you might guess, we always recommend you talk to an air technician or an experienced engineer before you make a final decision, but if you’re trying to gauge generally what size air compressor is right for your facility, here are the basics you need to know to size an air compressor the right way:

How Much Air Do You Need?

First things first — how much air do you need? To get the right size air compressor, you have to know how much air you need first.

To determine how much air you need, take inventory of your shop or factory.

  • What tools need air?
  • What is their CFM (cubic feet per minute) demand, each?
  • Will all of those tools be running at the same time?
  • If not, which tools will run at the same time? How much CFM will they need collectively?

Once you have a solid estimate of how much air you’ll need to run all of the tools in your facility, it’s a good idea to go ahead and add 30% to that total CFM number you came up with. This will help add a bit of a buffer for any air leaks and peak air requirements (we’ll talk about this more a little later).

How Much Pressure Do You Need?

Every machine requires a certain level of air pressure — identified as psig (pound-force per square inch gauge). Each of your tools may require a different psig, so it’s best to figure out what tool requires the highest psig. That number is the maximum pressure needed to run your tools. You’ll want to find an air compressor that can match that psig.

What’s Your Duty Cycle?

In other words, how often are you using your air compressor? For an in-depth definition of what a duty cycle is, and how to determine your needed duty cycle, check out this blog. The point of determining your duty cycle is to help you determine how much air you need, and for how long, so you can choose the appropriate air compressor control system. 

For example, if you’re intermittently using your air compressor to power a few small air tools in an auto garage or paint shop, you can choose from a number of smaller air compressors with simple start/stop or load/unload control systems.

If you’re using your air compressor constantly, and at fairly high speeds, then you’re probably going to need a larger compressor (or two) with a variable speed drive or variable displacement controls.

Duty cycle is an important indicator of the size air compressor you’ll need as well. Even if you’re only running your air compressor for short periods of time, if you need a ton of air in those 30 minutes, you’ll still need a bigger compressor.

Look At Air Compressors That Match Your Air and Pressure Requirements

With answers to the three questions above in hand, you’re ready to start looking at air compressors. Remember that there are a few different types of air compressors, so make sure you’re looking at an air compressor type that suits your facility. For example, a small machine shop won’t need a centrifugal air compressor. You will likely be looking at smaller reciprocating compressors.

You’ll also need to determine whether you need an oil or an oil-free air compressor. That choice will depend more on your application than the size of your compressor, but it’s an important distinction to make.

What About My Air Compressor’s Horsepower?

Here at TMI, we get questions about air compressor horsepower all the time. It is an easy way to categorize and talk about different sized air compressors, but you shouldn’t use horsepower to determine the right air compressor for you. We won’t get into the nuts and bolts of it all, but here’s the basic breakdown:

More efficient air compressors can do more with less horsepower.

The best judge of your air compressors’ ability is air pressure and flow, or psig and CFM. Those two numbers tell you everything you need to know about an air compressor’s capacity. Horsepower is an easy way to talk about different models, but it’s not a factor when you’re sizing an air compressor for your application.

Don’t Forget to Consider Peak Air Demand Requirements

And finally, before you go out and call up your air technician, there’s one last thing to consider — peak air demand requirements. Up until now, we’ve talked about how much air and pressure you’ll need in an everyday situation. But, as you know, not every day at your facility is the same. Sometimes it’s seriously hot in your facility. Sometimes you need to run some machines longer or harder than usual. It’s important to factor in peak air demand requirements when you’re sizing your air compressor, so you don’t run out of air when you need it most. We added on 30% of the estimated CFM in the first step for this exact reason.

Depending on your air system, you may need to size up slightly, or even consider implementing a smaller backup air compressor to relieve your main compressor during peak use. This consideration can be tricky, so it’s a good idea to talk with an engineer or air compressor technician to get a confident solution for your unique facility.

Sizing an air compressor takes a bit of math and a bit of research, but the effort is well worth it. Purchasing the right size air compressor for your facility means you save money upfront, and through the lifespan of your compressor, as you choose the most efficient option for your facility’s needs. If you’re stuck on any part of sizing an air compressor for your facility, the TMI team is here to help. No matter what you need, what size air compressor, or what type, our expert technicians can walk through your air requirements to match you with the most efficient air system for your facility. Give us a call at 800-875-9555 or contact us online today.


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