The metal was taken from the conditioning units at the DBH Services Business Centre in Middlewood Way, Carlton, Barnsley, at 7.45pm on Sunday, November 5.
The burglars also caused extensive damage to the units.
Detectives have now released CCTV images of three men they are tracing in connection with the incident.
A South Yorkshire Police spokesperson said: "Did you see any suspicious activity in the area at the time of the incident?
"Anyone with information is asked to report it via 101 quoting incident number 422 of 6 November. Anonymous information can also be given to Crimestoppers via 0800 555 111."