Generator type: one- vs. two-tank
The generator is the heart of any garage air compressor, but it’s also where air compressors are most different from one another. The first thing to consider when looking at garage air compressors is whether the compressor uses a one-tank or a two-tank design. In a one-tank, or one-stage, air compressor, air is taken into the tank one time only and compressed to its final pressure in a single stroke of the piston. This is in contrast to a two-tank, or two-stage, air compressor, in which air is compressed by one piston stroke, then pumped at pressure while being cooled to a second tank and compressed to an even higher pressure by a second piston stroke.
One-tank air compressors typically provide a maximum pressure of up to 150 psi, whereas two-tank air compressors can offer pressures up to 200 psi. Particularly at high pressures near the limits of a one-tank air compressor, two-tank compressors become more efficient thanks to the cooling step during the pumping between tanks. However, one-tank air compressors generally have higher cubic feet per minute ratings than two-tank compressors since air is being compressed to the final pressure with every turn of the engine.
Generator type: oil vs. oil-free
The piston that actually compresses air and pressurizes it requires lubrication to function properly. This lubrication can either come in the form of oil – which needs to be added to the air compressor regularly – or in the form of a Teflon coating around the piston that provides permanent lubrication.
In addition to requiring more frequent maintenance than their oil-free counterparts, oil-based garage air compressors tend to cost more and be bulkier since the internal design is more complex. However, oil-based garage air compressors typically last much longer if they are maintained properly over their lifetime. Still, if you are using your garage air compressor infrequently at home rather than for industrial work, it may be a long time before you wear out a less expensive oil-free air compressor. However, one additional consideration is that oil-based air compressors are much quieter than oil-free compressors, which can make a big difference if you’re working in your garage or during quiet times like at night.
Generator type: power source
Air compressors can either run on electricity or on gasoline, and which a compressor requires typically depends on the size, volume, and pressurization of a particular air compressor. For garage use, the vast majority of air compressors are powered by electricity rather than gasoline since it is cheaper, requires less maintenance, and makes it easier to start using the compressor. All of the garage air compressors in our review are powered by electricity.
The tank volume essentially describes the capacity of pressurized air that your air compressor can hold in a single pressurization and release cycle. Whether this number is important depends largely on what you are using your air compressor for. For example, if you are powering a pneumatic nail gun, where firing each nail uses a small amount of compressed air and the compressor has time to compress more air between each nail, tank volume is relatively unimportant. However, if you are using your air compressor to power a sander or a saw, where the air supply to the tool is relatively constant and high flow, then you will need a large tank volume in order for the compressor to keep up with the demand from the tool without running out of compressed air – such as the one found in a 60 gallon air compressor.
The performance of garage air compressors is described primarily by the pressure of air it can deliver – measured in psi, or pounds per square inch – and by the rate at which it can deliver air – measured in cfm, or cubic feet per minute. The pressure and delivery rate that you need depend largely on the tools you plan to use with your garage air compressor. When in doubt, opt for a more powerful compressor than you think you need since that way you will be able to power a more pressure-hungry tool later if you purchase one, rather than having to purchase an additional air compressor to go with that tool later.
Note that the motor with which a garage air compressor is equipped also plays a role in determining the compressor’s output pressure and delivery rate. As you would expect, a smaller motor will have a lower maximum pressure and delivery rate compared to a larger, higher horsepower motor.
Durability and warranty
Like any other tool in your garage, you should expect your air compressor to offer a long lifespan before needing to replace it – so durability is an important consideration. As discussed above, oil-free air compressors do not last as long as oil-based air compressors since the Teflon coating around the piston will eventually dry out and crack. However, you should also consider whether the motor itself, the electrical wiring, and the air tubing is durable and able to handle frequent jobs near maximum output – user reviews are the best way to determine this since many people rigorously test their air compressors after purchasing a new unit.
Also be sure to check the warranty on any garage air compressor, since this is an important fail-safe for your purchase and something that can provide peace of mind that your investment is protected.