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Older furnaces sometimes relied on gravity instead of a blower to circulate air. [1]Gas-fired forced-air furnaces have a burner in the furnace fueled by natural gas.A blower forces cold air through a heat exchanger and then through duct-work that distributes the hot air through the building. [2]
Heat is produced via combustion of fuel. A heat exchanger keeps the combustion byproducts from entering the air stream. A ribbon style (long with holes), inshot (torch-like), or oil type burner is located in the heat exchanger.
For energy-conversion heating devices their peak steady-state thermal efficiency is often stated, e.g., 'this furnace is 90% efficient', but a more detailed measure of seasonal energy effectiveness is the annual fuel use efficiency (AFUE). [10]
The annual fuel utilization efficiency (AFUE; pronounced 'A'-'Few' or 'A'-'F'-'U'-'E') is a thermal efficiency measure of space-heating furnaces and boilers.The AFUE differs from the true 'thermal efficiency' in that it is not a steady-state, peak measure of conversion efficiency, but instead attempts to represent the actual, season-long, average efficiency of that piece of equipment ...
Diagram of natural draft gas furnace, early 20th century. The first category of furnaces is natural draft, atmospheric burner furnaces. These furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The heat exchangers were vented through brick or masonry chimneys.
This degrades the efficiency of the reactor, so reaction conditions are designed to minimize this. Nonetheless, a steam cracking furnace can usually only run for a few months at a time between de-cokings. Decokes require the furnace to be isolated from the process and then a flow of steam or a steam/air mixture is passed through the furnace coils.
Oxyfuel CCS power plant operation. Oxy-fuel combustion is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated flue gas, instead of air. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible.
Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency (greater than 90% on the higher heating value) by condensing water vapour found in the exhaust gases in a heat exchanger to preheat the circulating water.