Contractor’s Guide to Portable Air Compressors
The construction trades are fueled by the power tool industry, which introduces countless new tools and accessories each year to help contractors work quicker, safer and more efficiently. While the latest cordless “wonder tool” typically captures all the attention, it’s pneumatic tools that dominate the work environment at most jobsites.
Air-powered pneumatic tools are popular with professionals for three simple reasons: they’re fast, reliable and durable. Fastening tools represent the most common construction-site pneumatics, including framing nailers, finish nailers, coil roofing nailers, metal-connector nailers, flooring nailers and staplers and cap staplers, which are used to attach asphalt-saturated felt, housewrap and thin foam sheets.
Some other air tools include:
- Drills
- Impact wrenches
- Die grinders
- Chisel hammers
- Cut-off tools
- Disc sanders
- Reciprocating saws
- Metal shears
- Ratchet wrenches
- Paint sprayers, both siphon and gravity-feed types
However, to get the most out of your pneumatic tools—and workforce—it’s important to match the tools and tasks to the correct air compressor. Here, we’ll examine several different sizes and types of pro-duty compressors, and give advice on choosing the most appropriate ones for certain jobs. But, before getting into any specifics, let’s take a brief look at the two basic types of compressors: electric and gas.
Electric vs. Gas
A vast majority of air compressors sold today have electric motors, but gasoline-powered compressors are also available. Electric compressors are preferred because they’re quiet, lightweight and affordable, and they don’t produce noxious fumes. Most electric compressors run on standard 110/120-volt household current, but larger models with motors exceeding two running horsepower typically require a 220/240-volt outlet.
Gas compressors cost more than electric compressors, but operate completely off the grid. They’re perfect for jobsites where electricity is limited or not available. To keep a gas compressor operating at peak efficiency, be sure to use the type of gas and oil recommended by the manufacturer. Caution: Gas compressors emit hazardous fumes. Never operate one in an enclosed, unventilated space.
Compressor Features
All portable jobsite air compressors consist of a motor and storage tank. The motor compresses air and then stores it under pressure inside the tank. As the pressurized air is released to power a tool, the pressure inside the tank drops. When the pressure reaches a certain level, the motor kicks back on and re-pressurizes the tank.
In a traditional compressor, the motor and tank work together as one integral unit. However, newer compressor designs have detachable tanks, which allow you to carry just the pressurized-air tank—not the entire compressor—right to the job.
Every air compressor has a maximum PSI rating, which represents the maximum pounds per square inch of air pressure produced. Portable jobsite compressors usually have a max PSI rating between 150 and 175 PSI, which is plenty of power since most air tools operate at around 90 PSI.
The size and power of a compressor’s motor is often indicated by its peak horsepower rating, which is almost meaningless since no motor operates at peak horsepower while under load. A more reliable rating is a compressor’s running horsepower, which is the amount of power sustained over a long period of use.
The size of the air tank is measured in gallons. If your work calls for constantly moving the compressor from room to room, such as when installing wood trim, consider a 4- to 6-gallon compressor with either a pancake-style tank or twin tanks. Both styles are compact, lightweight and easy to transport.
When running continuous-use tools, such as sander or die grinder, consider a large-capacity compressor with a 20-gallon or larger tank for greater air storage. Choose one with a vertical tank and dual-wheel dolly for easy transport across jobsites.
Other features to look for include a high-flow regulator, easy-open tank drain, protective roll cage and multiple quick-connect couplings (outlets) so you can run two or more tools from a single compressor.
Also, smaller compressors typically have oil-free pumps, which are convenient because they’re sealed bearings that don’t require lubrication. However, most large, industrial-duty compressors have an oil-lubricated pump, which you must monitor and change the oil regularly.
CFM Requirements
All air tools have a CFM requirement, meaning the amount of cubic feet per minute of air they need to operate at peak performance. The chart below lists some common air tools and their average CFM requirements when operated at 90 PSI. Note that the “average” is typically based on a 25 percent duty cycle, or 15 seconds out of every minute. That’s because most air tools, like nailers and wrenches, are used intermittently. To determine the CFM requirement for continuous-use tools, such as sanders and grinders, simply multiply the average CFM by four.
Final Word
With so many different sizes and types of compressors available, choosing the right one can be overwhelming. But just remember that the most important factor is to match the compressor to the tools and tasks. Make a list of the tasks, find the air tools to complete those tasks and check the CFM requirements of each tool. Then simply make sure any compressor you buy can provide the necessary air pressure to power those tools.
About the Author: Joseph Truini is a home-improvement expert who writes extensively about do-it-yourself home remodeling and repair, woodworking projects, and tools and techniques. He has authored six books and his work has appeared in several national magazines. He also writes for the Home Depot, where they carry a wide selection of nailers, compressors and other air tools.
