The Riverhead Fire Department responded to a report of smoke in Peconic Bay Medical Center radiology department shortly before noon Monday.
Firefighters went on the roof with a thermal camera to try to find signs of heat, according to First Assistant Fire Chief Joe Raynor.
He said a faulty heating or air conditioner unit may have caused the smoke, which staffers had smelled.
The fire department was on scene for about 45 minutes.
This call came on the heels of another Riverhead Fire Department call just after 11:30 a.m. at the recreation center in Glenwood Village. Riverhead Town fire marshal Craig Zitek said that smoke had been caused by a washing machine belt.