Buying guide for Best air compressors
A portable air compressor is an extremely useful tool. There are dozens of tasks it can help you perform, from filling tires, to framing out your loft, to grinding welds on auto body repairs.
There are also dozens of different models available, and a potentially bewildering range of specifications. Choosing a portable air compressor that meets your needs is far from easy.
How air compressors work
In essence, an air compressor is quite a simple mechanism. Atmospheric air is pulled into a chamber, where it is compressed by a motor. A tool is attached via a reinforced hose, and a trigger opens a valve, allowing the compressed air to power the tool.
In a few models, pressure is generated by a rotating impeller (it looks a bit like a fan blade), but in most models, it's done by a piston running up and down inside a cylinder. It's very much like the engine in your car or lawnmower.
In small, cheap air compressors the air produced is used straight away – the compressor runs continually. In larger models, it's stored in one or more tanks. The advantage here is that the compressor doesn't need to run all the time. Once the tank is full, the motor will switch off. When the pressure drops, the motor restarts automatically to refill the tank.
Testing portable air compressors
We spent 34 hours researching 78 different portable air compressors before choosing our favorite. We then purchased our top pick and tested it in the field to confirm our choice.
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Types of air compressor
Though they might look very different from the outside, air compressors can be broken down into a few basic types:
All of the portable air compressors we selected are powered by electricity and can be plugged into an ordinary household outlet. Larger electrical models may have more demanding requirements, but these are normally stationery and more suitable for professional workshops and factories. Gas-powered air compressors are often big, powerful units used in commercial environments or construction sites, as well as situations where an electrical supply is unavailable.
The majority of air compressors are lubricated with oil, particularly the more powerful models. Oil levels should be checked regularly and changed periodically. It's a quick and simple maintenance routine that ensures a long working life. Indeed, these compressors are known for their long-term durability.
Oil-free air compressors have Teflon-coated cylinders that don't need lubrication. There's virtually no maintenance, so it's no surprise they are popular.
The drawback with oil-free models is that the Teflon lining will eventually wear, and cannot be replaced. There's no solution other than buying a new compressor. While it sounds drastic, it's a slow process, and a high-quality, oil-free portable air compressor should last many years.
Expert Tip
Be very choosy in choosing a portable air compressor. Consider all the potential uses you may have from tires to toys. Do you need a home and car plug? Do you need a cordless model to get to the backyard shed to pump those mower tires?
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Air compressor specifications
To understand portable air compressor performance, you need to understand the terminology, and how important each aspect is.
Air compressor specification sheets should supply you with four figures:
Horsepower
The horsepower rating tells you how hard the motor can work. The higher the horsepower, the quicker the compressor will get to working pressure, and the faster it will fill the tanks – and refill them while in use.
CFM
This is a measure of airflow, and the most important characteristic of any air compressor. You can have low horsepower, and the pressure will build up eventually. If you have low airflow, some tools simply won't work – there isn't sufficient power to drive them.
If you only need a compressor to inflate tires or blow up an air bed, low airflow doesn't have much impact. If you're using a nailer, grinder, or impact wrench, then the right output is absolutely vital. All air tools have a cfm rating. If your air compressor doesn't match or exceed that rating, the tool will not work.
The reported airflow for an air tool or compressor should be measured at 90 psi. The figure is used to give a standard for comparison, rather than meaning the tool must be used at 90 psi. Beware of cfm numbers quoted at different psi levels. It can be used as a way to make the compressor appear more powerful than it really is.
Check the air tools you expect to use before buying a portable air compressor. A brad nailer can have an airflow as low as 0.5 cfm at 90 psi, but a framing nailer might require 2 to 2.5 cfm, and a 1/2" impact wrench could need 4 cfm.
You can always turn the pressure of a big compressor down, but you can't turn a small one up beyond its stated cfm rating.
Expert Tip
Consider if you want to purchase more than one unit. Do you need them in dual cars to offset not having roadside assistance?
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PSI
This is the actual air pressure generated. In theory, a 3-gallon tank full of air at 150 psi has 30% more air in it than the same size tank at 100 psi. So, psi could be used to compare how long two compressors would run between refills.
In practice, even the smallest, cheapest portable air compressors will generate 100 psi or more. Anything above that should be more than adequate for DIY and small workshop use.
Tank size
Whether tank size is important or not will depend on the kind of work you do. If you're only looking for a compressor for general inflation duties, you probably don't even need a tank.
If you run a selection of air tools, a tank gives you the advantage of creating an air reserve: the compressor fills the tank to a pre-set pressure, then stops working until the pressure drops. It makes for a quieter working environment, too.
Expert tip
Be prepared. Most inflators need some recovery time between inflations to prevent burnout, so take that recovery time into account before you start.
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Twin tanks can be useful if two people use the same compressor simultaneously, particularly if they're using different tools. With a large tank, a pressure drop could adversely affect both tools. With twin tanks, each tool can be supplied more effectively.
However, some air compressors that appear to have twin tanks, strictly speaking, do not. Two cylinders are used to save overall space, but they are in fact linked, and act as one. This is often true even if two outlets are offered. Read the manufacturer information carefully to determine whether the tanks operate independently.
Key specifications summary
Producing the right amount of airflow (the cfm rating) is absolutely vital. Get it wrong and your tools won't run.
High horsepower is good because it means your portable air compressor works hard and fast.
High psi is nice in terms of run time, but not the most important element.
A larger tank will let you work longer.
Other air compressor considerations
If portability is important, look at how much the compressor weighs, and whether there's a carry handle or convenient part of a frame to pick it up.
It's nice to have clear, easy-to-read gauges. Also, controls that can be adjusted with gloved hands make your work flow much more smoothly.
A portable air compressor with a low amp draw at start-up is less likely to trip your household breakers.
With lubricated models, a sight glass makes checking oil level simple.
A kit of accessories is a useful addition, but they're usually only good for inflation tasks. High-performance portable air compressors tend not to include them.
What does a good portable air compressor cost?
Inexpensive
If all ever do is inflate your car tires, you can buy a small, tankless air compressor for under $20. It will be a bit noisy, slow, and it might not last very long, but it will do the job.
Mid-range
An entry-level machine capable of a wide range of inflation tasks, including powering modest air tools like brad nailers and staplers, will cost between $60 and $140. The actual cost depends very much on power output. With tools like this you often get an accessory kit.
Expert Tip
If noise is an issue for you, remember to check the decibel rating of the model you're considering before you buy.
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Expensive
If you want to undertake serious do-it-yourself, auto repair, or other workshop activities, you'll need a minimum of $200. The best portable air compressors cost over $300. However, for that money, you'll get a hard-working, reliable tool that ought to last a lifetime.
