Furnaces

Furnaces are heating appliances that generate heat by burning fuel or converting electrical energy to heat, used for space heating in buildings or for industrial processes. They typically drive hot air through ducts or circulate hot fluids.

Residential furnaces come in gas, oil, or electric varieties. Gas furnaces burn natural gas or propane with a burner; oil furnaces burn heating oil; electric furnaces rely on electric resistance heaters. Industrial furnaces encompass a wide range: reverberatory, cupola, electric arc, and blast furnaces used for metal processing, glass, ceramics, and chemical production. In some systems, heat is transferred via radiant, convection, or conduction.

How they work: combustion occurs in a chamber, heat is transferred to a heat exchanger, and the warmed air or fluid is distributed via ducts or piping. Modern furnaces use controls, thermostats, and safety devices to regulate temperature and shut down the system if carbon monoxide or flame failure is detected. Condensing models recover more heat by cooling exhaust gases.

Efficiency and safety: efficiency is expressed as AFUE for residential units; higher AFUE indicates less fuel is wasted. Emissions depend on fuel and technology. Potential hazards include carbon monoxide, fires, and gas leaks; proper venting, installation, and annual maintenance are essential.

Maintenance and development: regular filter changes, burner inspections, and vent checks prolong life. Advancements include better insulation, sealed combustion, electronic controls, and condensing designs. In the energy transition, heat pumps and boilers are increasingly used alongside furnaces.