The operating temperature of the ballast should be no hotter than 90° to 150° Fahrenheit. You should have the ballast on a brick, or a surface that is rated for these temperatures. You check a ballast to see if it is running to hot by touching the outer housing of the ballast with a kitchen match, if it catches fire your ballast is running too hot. It is best to have the ballast in a air conditioned area to help the ballast to run more efficiently for longer. A ballast that runs hot will quit working sooner or later. Some customers have fans & blowers on the ballast to help the ballast run cooler.