They have been operated with wood, coke, coal, trash, paper, natural gas, fuel oil as well as whale oil for a brief period at the turn of the century. These furnaces could be made to work with any fuel simply by adapting the burner area. The system was simple, had few controls, a single automatic gas valve, and no blower.

This method of heating worked because warm air rises. The pipes would channel the warm air into floor or wall vents inside the home. Air circulation depended on large, upwardly pitched pipes constructed of wood or metal. The heat exchangers were vented through brick or masonry chimneys. These furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The first category of furnaces is natural draft, atmospheric burner furnaces. The term furnace also refers to the various types of metallurgical furnaces, used for smelting and other metalworks, as well as industrial furnaces, which are used in various industrial applications such as chemical plants and providing heat to chemical reactions.ĭiagram of natural draft gas furnace, early 20th century. Furnaces that are used to boil water are called boilers. Furnaces primarily run on natural gas or electricity. Fuel efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency). Waste gas and heat are mechanically ventilated through PVC pipes that can be vented through the side or roof of the house. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. The most common fuel source for modern furnaces in North America and much of Europe is natural gas other common fuel sources include LPG (liquefied petroleum gas), fuel oil, wood and in rare cases coal. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boiler or residential hot water boiler. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. The name derives from Latin word fornax, which means oven. Furnaces are mostly used as a major component of a central heating system. A furnace, referred to as a heater or boiler in British English, is a heating unit used to heat up an entire building.

Best heat furnaces