Below is a list of Oil Boilers manufacturers from Fresno, California. Oil boilers are tanks or vessels that use oil to generate thermal energy that is circulated to provide residential, commercial and industrial heating. Oil boilers may either use oil as fuel for the furnace, which in turn heats water that circulates through radiators, baseboards or other heat exchangers, or oil may replace the water generally found in boilers and produce hot gases that travel through the piping system.