Is there a General Rule?
There is no real general rule applicable for all circumstances and in all conditions. It is best to first determine how much air you need. After that you need to know how often you will use your compressor.
As a guideline, professional piston compressors are designed to work with a maximum operating duty between 25% for the smallest models, to 75% for the bigger ones.
Industrial compressors can run more intensively and in more severe and heavy duty condition. The more often you use your compressor, the more likely a screw compressor will be more efficent and a more suitable solution.
