Determining the right size air compressor for your shop depends on several factors. The main considerations are:
- How many air tools you need to run at once
- Air requirements (SCFM) of each tool
- Air tank size needed
- Electrical power available
- Noise level
- Budget
In general, you want an air compressor that can handle the peak air demands of all your tools running at once, plus having a reserve to fill up your air tank. Most small to medium sized shops will require a compressor in the 5-10 horsepower range. Larger industrial shops may need 20-30+ HP compressors.
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Air Tool Requirements
The first step is to make a list of all the air tools you need to run in your shop. This includes tools like:
- Air impact wrenches
- Air ratchets
- Air drills
- Air sanders
- Air grinders
- Air spray guns
- Air hammers
- Air die grinders
- Inflators
- Blow guns
- Air chisels
- Tire changers
- Air staplers
- Air nailers
For each tool, you need to determine its:
- SCFM (standard cubic feet per minute) rating. This tells you how much airflow it needs.
- Number of tools you plan to run at once. For example, you may have 4 air impact wrenches that need to run simultaneously.
Add up the SCFM for all tools running at once to determine your shop’s total CFM requirement.
As an example:
| Tool | SCFM | # Needed | Total SCFM |
|---|---|---|---|
| Air impact wrench | 10 | 4 | 40 |
| Air sander | 6 | 2 | 12 |
| Air grinder | 8 | 1 | 8 |
| Total | 60 |
For this example shop with 4 impact wrenches, 2 sanders, and 1 grinder running simultaneously, the total CFM needed is 60 SCFM.
Air Tank Size
The air tank on the compressor provides a storage reservoir for compressed air. This allows the compressor motor to turn off periodically while still having air available.
Larger tanks are better since they extend the amount of run time between cycles. Most shops will want a minimum 60-80 gallon tank. Busy shops with high air demands may need up to a 120-240+ gallon tank.
The tank size also provides a buffer if multiple tools start up at once. The more tools demanding air simultaneously, the bigger tank you need.
As a rule of thumb, figure around 2-4 gallons per SCFM of air capacity. So using the example above requiring 60 SCFM, you would want an 120-240 gallon tank.
Compressor Horsepower
With the CFM and tank size determined, next is selecting the right compressor horsepower (HP).
The compressor HP needs to be large enough to:
- Produce the required SCFM airflow
- Quickly replenish the air tank
- Run continuously without overheating
Most small to mid-sized shop compressors are in the 3-7.5 HP range. Some guidelines:
- 3-5 HP – Handling 1-2 smaller pneumatic tools
- 5-7 HP – Good for most small auto or home shops running several tools
- 7-10 HP – For larger demands with multiple tools running simultaneously
- 10-15 HP – For heavy usage with bigger tools like sanders and grinders
- 15-30+ HP – For industrial shops running multiple large tools at once
Going back to the previous example requiring 60 SCFM max airflow, a 7.5-10 HP compressor would be ideal. This provides some extra power to quickly refill the tank.
Electric vs Gas Models
Air compressors are available in electric or gas engine models. Considerations for each:
Electric
- Lower upfront cost
- More maintenance required
- Limited by circuit amperage – may require 220V outlet
- Suitable for indoor use
- Quieter operation
Gas
- Higher initial cost
- Less maintenance
- More power in small packages
- Can handle longer duty cycles
- Need well ventilated area
- Louder operation
For most small shops, an electric compressor is the easiest and most economical choice. Units up to about 7.5 HP can run on 220V circuits. Larger electric models may require a dedicated high voltage line and cost significantly more.
Gas compressors don’t rely on power cords or outlets. Their advantage is providing more power in a compact unit. This makes them a good option when electricity supply is limited or portability is needed. The trade-off is they require fuel, oil, more maintenance, and are noisy.
Other Considerations
Here are some other factors to keep in mind when selecting an air compressor:
Noise Level
- Electric compressors tend to be quieter than gas models.
- Look for ones advertised as “Quiet” or a decibel rating less than 75-80db.
- Consider purchasing a sound dampening enclosure if installing in a workspace.
Build Quality
- Choose reputable brands known for quality manufacturing.
- Look for high duty cycle ratings – preferable 100% continuous use rating.
- Consider cast iron cylinders and pumps for extended durability.
- Make sure electric motors are protected and have overload protection.
Air Filtration
- Multi-stage filtering ensures clean, dry air for tools.
- Filters help remove moisture and particles from the air.
- Easy access panels allow replacing filters when needed.
Air Dryer
- Optional accessory that removes moisture from the air.
- Helps prevent water condensation in air lines.
- Recommended if operating air tools in humid environments or cold temperatures.
Portability
- Wheeled compressors allow moving them around the shop as needed.
- Make sure the handle is ergonomically designed for comfort.
- Locking casters help keep it stationary while in use.
Top Air Compressor Brands
Some of the top brands known for making quality air compressors include:
- Ingersoll Rand
- Quincy
- Campbell Hausfeld
- California Air Tools
- Senco
- DeWalt
- Makita
- Industrial Air
- Porter Cable
- Rolair
Sticking with major brands provides some reassurance you’re getting a well-designed compressor built to last. Be wary of purchasing “off brand” compressors that may cut corners and won’t hold up under heavy daily use.
Air Compressor Sizing Examples
Here are two example scenarios for determining the right air compressor size:
Example 1
Small auto repair shop running:
- 2 air impact wrenches (5 SCFM each)
- 1 air ratchet (4 SCFM)
- 1 air drill (6 SCFM)
Total CFM: 5×2 + 4 + 6 = 20 SCFM
Tank size: 50-60 gallons
Horsepower: 5-7 HP
This shop would do well with a 5-7 HP electric compressor and 60 gallon tank. A unit rated for 100% duty cycle is recommended since it will get heavy use.
Example 2
Larger garage running:
- 3 air sanders (10 SCFM each)
- 2 air impacts (13 SCFM each)
- 1 spray gun (8 SCFM)
- 2 air drills (4 SCFM each)
Total CFM: (3×10) + (2×13) + 8 + (2×4) = 78 SCFM
Tank size: 120-200 gallons
Horsepower: 10-15 HP
This shop needs a 10-15 HP electric compressor with a large 120+ gallon tank. May also want to consider an add-on air dryer.
Conclusion
Choosing an adequately sized air compressor is crucial for providing enough compressed air to power all your pneumatic tools properly. The key steps are:
- Determine the maximum SCFM airflow needed for all tools running at once.
- Select an appropriate air tank size, typically 60-240 gallons.
- Choose a compressor with horsepower capable of supplying the required SCFM.
- Consider noise level, build quality, air filtration, and portability.
- Pick a major brand known for manufacturing quality compressors.
Taking the time to properly size your air compressor will ensure it provides reliable, trouble-free service and keeps your air tools running optimally for years to come. Oversizing allows room to add more tools down the road. Undersizing can lead to frustration from lack of power.
Use the air consumption information provided and examples shown to help determine the right compressor system for your particular shop needs. This helps optimize performance and efficiency for your pneumatic tool operations.