An air compressor can be a great way to save time and manual labor on your next project. A wide range of pneumatic tools is available. These pneumatic tools use air to power them, instead of electricity. There are operational costs to run an air compressor, but selecting the right air compressor for your needs will help you operate your machine efficiently.
How much does it cost to run an air compressor? The cost of running an air compressor will depend on the size of the compressor and tank, how you operate the unit and the efficiency of the compressor and motor. You can easily calculate the cost to run your air compressor based on your needs.
There are many variables involved in the cost of operating an air compressor. To understand the costs of energy to run one, you must know how it works. We’ll explain the basics of how an air compressor works, how to make sure your air compressor is as efficient as possible, and what to look for when purchasing an air compressor for your needs.
Do Air Compressors Use a Lot of Electricity?
For many workshops, compressed air is one of the most inefficient sources of energy. Some rules of thumb estimate about 10% of the power input is usable output. Another metric says that 1 horsepower (HP) of compressed air takes 8 HP of electricity to generate. However, how much electricity your compressor will use depends on the efficiency of the motor and how you use it.
To determine how much electricity your air compressor uses, or how much one might use if you are considering buying one, ask the following questions:
- How long is the air compressor being used?
- What tasks is the compressor being used for?
- Where will the compressor be located while it’s in use?
If you already own and use an air compressor, figuring out how much power your air compressor uses is pretty straight forward. The manufacturer Quincy Compressors provides recommendations on how to do it:
- First, use a timer to track how long the compressor on your machine runs while you use it. Even with continuous use, the air compressor’s motor will only run while trying to pressurize the tank. If you continuously use air for four hours, the compressor might run intermittently, trying to repressurize the tank. You should be able to hear when the compressor cycles on and off.
- Next, figure out the power consumption. The power draw may be listed in watts, amps, or even horsepower. This information might be on the nameplate of the air compressor, on the motor, or in the operation manual.
- If power is listed in watts, divide by 1000 to get kilowatts (kW).
- If power is listed in amps, multiply the amps by the voltage. Most residential outlets provide 120V power. Amps times volts will give you watts. If a 20 Amp unit is connected to a 120V outlet, the power will be 20 x 120 = 2400 W, or 0.24 kW.
- If power is listed in horsepower, you can look up the efficiency of the motor, then assume a power factor (typically around 0.9). The power draw will be HP x efficiency x power factor divided by a conversion factor of 746. This will give you the watts for the motor.
3. Multiply by the number of hours (or minutes as a decimal of one hour) to get the kilowatt-hours (kWh) of power used. For example, if your air compressor uses 560 W, and it runs for 2 hours, 560 W x 2 / 1000 = 1.12 kWh, then you used 1.1 kWh.
4. Determine the cost of your power from the utility company. Most utility companies will charge for power based on the kWh used, though sometimes the total cost may include a demand charge, which is a fee based on the peak power draw used at any one time. In California, the cost of electricity might be $0.29 per kWh. For the 560 W air compressor, this would cost 1.1 kWh x $0.29 = $0.319.
However, if you don’t own your own air compressor yet, and you’re not sure how long you will run your air compressor or how much power one might use, then you might be able to calculate it based on your needs. To do that, we’ll first explain how an air compressor works.
How Do Air Compressors Work?
Inherent to its name, an air compressor is a machine that compresses air. Air is a compressible gas that behaves like an ideal gas. Khan Academy has a lesson on how to use the ideal gas laws to predict how air behaves.
An air compressor uses electricity to compress air and store it in a pressurized tank for future use. Some air compressors may not have a storage tank. These types of air compressors compress air on demand. They generally have lower pressure ratings than compressors with tanks.
Through the compression of air, the air compressor converts the power in your energy source, like electricity or gas, into potential energy. This potential energy in the compressed air is converted into kinetic energy when it’s used.
All these conversions are not perfectly efficient, which means in each stage of the process, the air compressor doesn’t convert all the power into potential energy, and not all the potential energy gets converted to kinetic energy. The extra energy is converted to sound, heat, or vibrations.
Most air compressors utilize what is called a positive displacement method for air compression. The air enters the compressor through an inlet into the chamber of a piston. The piston compresses the air before releasing it into the storage tank.
Some air compressors use a single stage to compress the air to about 125 psi (pounds of force per square inch), but for higher pressures, the compressor may use two stages. The compressed air from the first stage enters a second piston that compresses it even further. These compressors will be called a single stage compressor or a two-stage compressor, respectively.
The motor on the air compressor moves the crankshaft on the piston, which drives the piston up and down. The motor may require electricity or gasoline as the source of energy to drive the crankshaft. From the motor to the crankshaft, then from the crankshaft to the piston, finally from the piston to the air, each process loses efficiency.
At first, the pressure in the storage tank will likely equal atmospheric pressure, which is the pressure of the normal air we breathe. As the compressor fills the tank, the pressure will increase. Each tank is rated for a maximum pressure before it could explode.
The air compressor itself will have its own pressure rating as well. Between the two, the air compressor will have an overall safe maximum operating pressure, and the manufacturer will implement controls to prevent that pressure from being exceeded.
The user can set a pressure rating for the outlet airflow, which will match the recommended pressure for the tool they are using. The user can also typically set a minimum pressure for the tank. A pressure sensor in the tank will monitor the pressure in the tank so that when the pressure drops below the threshold set by the user, the air compressor will cycle on to increase the pressure up to the maximum.
Various tools and accessories can be connected to the air compressor. They will have their own recommended pressure (in a unit called PSI) for best use, as well as rated airflow (in cfm). Knowing the ratings on the tools you intend to use will help you select the best air compressor for you.
How Long Will My Air Compressor Run?
If you don’t already own your air compressor and are trying to calculate the operating costs of using an air compressor, you might wonder how long the air compressor will run while you’re using it. First, you should try to estimate the amount of compressed air you will need by researching the tools you intend to use.
Some examples might include running an impact wrench for an hour at 5 cfm at 125 psi, a palm sander for four hours at 2.2 cfm at 90 psi, or a framing nailer for eight hours at 2.2 cfm at 90 psi. Gather up the list of all the tools you might need and how long you might use them for on an average day (or week). You can determine the total volume required by multiplying the cubic feet per minute by the number of minutes you will run the tool.
If you have different pressure requirements, estimate the total volume at the pressure setting for your tank. Higher pressure in your tank will mean that you can run your tools longer. Let’s take a 200 psi tank, for example, with the tools we listed above, and convert the total volume of air to 200 psi.
The volume of air can be calculated from Boyle’s Law, which states the Volume of Air at atmospheric pressure = the volume of compressed air x the pressure of the air divided by the atmospheric pressure.
| Tool | Volume of Compressed Air Required | Volume of Uncompressed Air Required | Volume of Air Required in 200 psi Storage Tank |
| Impact Wrench (25% intermittent flow) | 5 cfm x 60 mins = 300 cf x 25% = 75 cf | 75 cf x 125 psi / 15 psi = 625 cf | 625 cf x 15 psi / 200 psi = 46.9 cf |
| Framing Nailer (10% intermittent use) | 2.2 cfm x 480 mins = 1056 cf x 10% = 105.5 cf | 1056 cf x 90 psi / 15 psi = 6336 cf | 633 |
| Total | 4426 cf | 322cf |
To convert cubic feet to gallons, multiple by 7.48. For 332 cubic feet of 200 psi compressed air, we would need 2483 gallons of compressed air. For a twenty-gallon storage tank, the tank would need to be refilled over 124 times!
Thankfully, the air compressor will start recharging the tank based on the minimum pressure set. Depending on how often you run the tool, you may need to wait to let the tank recharge from time to time. A general rule of thumb might be to have one to two gallons of tank capacity for the maximum airflow tool you plan to use. For example, if you use a 6 cfm tool, perhaps choose a 12-gallon tank.
By pressurizing the tank to the maximum rated pressure and setting the outlet valve pressure to the desired tool pressure, you can make the tank fill last much longer. However, make sure to adjust the outlet pressure to the correct tool pressure because you could damage your tools if you expose them to higher than their rated pressures for long periods of time.
Many air compressors will advertise a “quick recovery rate.” This means that the compressor will work very quickly to try to refill the tank while it’s in use. The recovery rate will be quicker with larger motors and compressors.
If you want to minimize the size of your tank, but are concerned that you might have to wait for the tank to refill, look for an air compressor with a higher horsepower motor. The maximum horsepower motor you will be able to connect to a 120 V residential outlet will be about 2 HP. Larger sizes would require an electrician to wire the air compressor to a dedicated circuit.
How Can Air Compressors Save Energy?
Air compressors might save a lot of time and manual labor for the user, but air compressors are not an efficient use of energy. As mentioned already, compressing air takes a lot of electricity to produce a useful, continuous amount of air to be used in pneumatic tools. However, depending on the power tool, residential pneumatic tools might use less energy than their residential electrical versions.
Pneumatic tools are famous for being much stronger than their electric counterparts, and even much more powerful than battery-powered electric tools. In small scale residential applications, this is especially true. Typically, in industrial or commercial settings, the size of the tools is much larger. At larger sizes, motors are much more efficient.
Compare an electric palm sander to a pneumatic palm sander. One 12,000 rpm electric palm sander uses 3 A on a 120 V residential outlet. A similar 12,000 rpm pneumatic palm sander needs 2.2 cfm of air at 90 psi.
Calculating Horsepower
The horsepower required to compress the air can be calculated as follows:
HP = [144 N P1 V k / (33000 (k – 1))] [(P2 / P1)(k – 1)/N k – 1] x 1.1
| Where: N = the number of compression stages P1 = initial pressure, which is atmospheric pressure at 14.7 psi P2= the final pressure desired k = The adiabatic expansion coefficient, 1.41 (a constant conversion factor) V = the airflow of the tool in cfm |
The horsepower required for the 2.2 cfm of air required for the drill is about 0.306 HP, or about 228.5 W. The electric version uses about 360 W. For a run time of one hour each, with the same electricity rate of $0.29/kWh, the pneumatic tool would use just 6 cents of electricity while the electric one would use 10 cents.
Take another example, a corded impact versus a pneumatic. One electric version providing 345 ft-lbs of torque uses 7.5 A at 120 volts, while the pneumatic one uses 5.3 cfm. The electric uses 900 watts while the pneumatic one uses 665 W. In this instance, for one hour, the pneumatic tool would use just 19.3 cents of electricity while the electric one would use 26 cents.
When considering whether you want to purchase a pneumatic tool or electric version, review the power ratings to confirm that the pneumatic tool is more efficient than the electric version. Some tools, such as nail guns, are more commonly found in pneumatic options. Other tools, such as handheld drills, make more sense as an electric option.
If you live in an area where electricity is very expensive, you can reduce the overall costs of using tools by charging your air compressor tank when electricity rates are low. Most utility companies have rate structures where electricity might be cheaper during off-peak hours.
Off-peak hours are hours of the day when fewer people use electricity, such as late at night, overnight, or in the early morning. If you use your power tools during the day, when everyone else is using power, the electricity costs may be much higher.
By charging your tank at night and using your pneumatic tools during those peak times instead of electric tools, you could save more money on your utility bills.
How to Reduce Air Compressor Power Consumption
Every machine will operate the most efficiently when all of its components are in good working order. Making sure that all components of your air compressor are maintained properly and are in good working order. CAGI, the Compressed Air and Gas Institute, recommends several ways to save energy when using your air compressor.
All tubes and accessories should be clean and free from oil, dirt, dust, and debris. Make sure they are stored in a dry, safe place, away from direct sunlight and weather. Plastic can start to degrade in sunlight, while metal components could rust or tarnish if left damp. Keep the power cord safely wound up when not in use, so that wire insulation doesn’t get knicked or pinched. Do not yank the plug from the outlet, which could cause strands of wires to break inside the cord.
Moreover, if your air compressor uses oil, the oil needs to be changed, much like a car needs an oil change to operate correctly. Many compressors need oil for the parts to move smoothly inside. The oil may leak into the air or burn over time. If the oil degrades or gets too low, the air compressor will operate less efficiently or even fail.
The motor may need a belt to turn the crankshaft that moves the piston. Inspect the belt regularly for knicks or wear. If the belt is old, it might slip, which causes the air compressor to be less efficient. Replace the belt regularly, more often with request use. If the belt breaks, the air compressor will stop working, but could also damage other components in the process.
To reduce other losses in the system, consider the following:
- Reduce the total length of hose from the tank to your tool. As air moves the hose, it will encounter friction against the walls of the hose. The longer the hose, the more friction, the more energy it will lose. Additionally, if there are any kinks, crimps, or fittings, those will also create friction losses in the system.
- Make sure the air compressor is intaking clean air. While you might usually use your compressor in a workshop, garage, or construction site, which typically are sources of dust and debris, contaminants in the air can damage the compressor over time while also making the compression process less efficient.
- Fill the tank when the air temperatures are cold. Cold air is easier to compress than warmer air. Additionally, higher humidity can also make the compressor work harder. If your workshop or garage is warmer than outdoors and your air compressor is portable enough, move the compressor outside while it’s filling.
Sound also dissipates more quickly outdoors, which can help prevent hearing loss due to sustained, loud noises. Compressing air also produces heat, which needs to be dissipated from the air compressor. The heat will dissipate more quickly in cooler temperatures and draftier/windier areas.
- Fix leaks in the system. Air leaks can often be heard through hissing sounds, but some smaller leaks may not be audible. Leaks often occur around fittings, such as the hose connections, pressure regulators, joints, and disconnects. Make sure all gaskets are in good condition and replace if the rubber hardens, wears down, or breaks down.
Use plumbers tape on fittings to help reduce air leaks and tighten down all threaded fittings properly, without over-torquing. You can fill a spray bottle with soapy water and spray carefully around fittings to detect leaks that aren’t audible while in use. Shut the compressor down to disconnect any fittings that need to be further tightened.
Newer technologies and advancement in motors and compressors have improved the efficiency of many pieces of equipment. Look for direct drive or electrically commutated motors, which eliminate the need for a belt and pulley system to drive the motor. These motors are harder to service and maintain, but have much higher system efficiencies than belt-driven motors.
Pick an air compressor that is large enough for your needs, but not much larger. If most of the tools you plan to use are 125 psi or 150 psi, selecting a compressor with a higher maximum pressure may reduce the time required to fill the storage tank, it will also take more energy to operate.
The air tank should be emptied regularly, as there is a risk that condensation could build up in the tank due to the temperature differences when compressing the air. If the water sits in the tank too long, the tank could rust inside and weaken the walls of the tank. The weakened walls could burst when the tank is filled close to its maximum pressure.
Summary
Compressed air is an inefficient source of energy. The cost of using an air compressor to power may still be less than the cost of operating electric power tools. To determine how much running your air compressor will cost, determine what type of tools you plan to use, how long you plan to run them, and what the cost of electricity is in your area.
By maintaining your air compressor properly and implementing a few good habits, you can save power and costs in the lifetime of your machine.
Here are a few abbreviations and units used in this article for quick reference:
- A: Amps, the flow of electricity
- CFM: Cubic feet per minute, a volumetric flow rate, used to describe the flow required for a pneumatic tool, sometimes expressed as V
- CF: Cubic feet, the volume of a cube with dimensions of 1 foot on each side, equivalent to 7.48 gallons
- HP: Horsepower, another unit for power, usually to define the power of a motor
- kW: Kilowatts, one thousand watts
- kWh: Kilowatt-hours, the energy of electricity, used to measure the work performed
- PSI: Pounds of force per square inch of surface area
- RPM: Rotations per minute, the number of time a machine spins per minute
- W: Watts, the power of electricity
- V: Volt, the pressure of electricity, or the potential for it to do work