Nesconset Fire Department responds to an activated fire alarm at the Old Nesconset Elementary School next to fire headquarters. Arriving units encounter a smoke condition in the building. The alarm is retransmitted as a structure fire bringing units from St. James, Lakeland, Ronkonkoma and Centereach to the scene. The problem was found to be within a heating unit. The unit was shut down, the building vented and all units were back in service within an hour.