Do you have vents that blow air? In that case, there is a furnace that burns natural gas, and that burning gas heats air that is pushed though duct work to the vents into your living areas.
Do you have radiators? In that case, there is a furnace that burns natural gas, and that burning gas heats water than can either be pumped to the radiators or heated enough to be turned into steam that goes into the radiators.
Latest Answers