**Types of Furnaces:**
Natural Draft Furnaces:
– Atmospheric burner furnaces with heat exchangers built within an outer shell.
– Depended on upwardly pitched pipes for air circulation.
– Operated with various fuels and required daily maintenance for solid fuels.
– Later adaptations included electric blowers for improved air distribution.
– Control was often manual based on fuel amount and air damper position.
Forced-Air Furnaces:
– Replaced older systems and were moved by blowers.
– Designed to accommodate air-conditioning systems.
– Energy efficiency ranged from 50% to over 65% AFUE.
– Bulky compared to modern furnaces.
– Used large chimneys for flues.
Forced Draft Furnaces:
– More compact with steel heat exchangers.
– Equipped with combustion air blowers for increased fuel efficiency.
– Designed to work with central air-conditioning systems.
– Physically smaller than previous styles.
– Some models featured multi-speed blowers.
Condensing Furnaces:
– Achieve between 90% and 98% AFUE.
– Capture latent heat from exhaust gases in a secondary heat exchanger.
– Remove most of the heat energy from exhaust gas.
– Vent pipes are often PVC to prevent corrosion.
– Deliver 25% to 35% fuel savings over a 60% AFUE furnace.
**Furnace Output Control:**
Single-Stage Furnaces:
– Have only one stage of operation, either on or off.
– Relatively noisy and always run at the highest speed.
– Pump out the hottest air at the highest velocity.
– Relatively inexpensive for installation.
– Blower motors consume more energy and are less efficient.
**Heat Distribution Methods:**
Intermediary Distribution System:
– Furnace transfers heat through an intermediary distribution system.
– Boilers provide hot water for bathing and washing dishes.
– Older air convection systems rely on passive circulation.
– Modern warm air furnaces use fans for forced-air heat.
– Ductwork can be made of sheet metal or plastic flex duct.
**Related Concepts:**
Forced-Air Gas:
– Related to the forced-air furnaces category.
Jetstream Furnace:
– Possibly related to the forced-air or forced draft furnaces.
Outdoor Wood-Fired Boiler:
– Possibly related to natural draft furnaces.
Masonry Heater:
– May have similarities with certain types of furnaces.
**Additional Resources:**
Practical Heating Technology by Johnson & Standiford
Furnace entry in Encyclopædia Britannica
US Dept. of Energy resources on furnaces and boilers
Handbook on Single, Multi & Variable Speed Furnaces by Ahmed
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A furnace (American English), referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system.[clarification needed] Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boilers or residential hot water boilers. 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. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency).
Definition from ChatGPT:
Furnace (central heating):
A furnace, in the context of central heating, is a heating system that generates and distributes heat throughout a building or home. It typically burns fuel such as gas, oil, or electricity to produce heat, which is then circulated through ducts or pipes to different rooms via vents or radiators. Furnaces are a common type of heating system used to maintain a comfortable indoor temperature during cold weather.