Annual Fuel Utilization Efficiency (AFUE)
An indication of how well a furnace converts energy into usable heat. The rating is expressed as a percentage of the annual output of heat to the annual energy input to the furnace.
Atomize
The process by which a liquid is converted into a fine spray
Combustion
The process by which a fuel is a ignited in the presence of oxygen
Condensing furnace
A furnace that contains a secondary heat exchanger that extracts latent heat by condensing exhaust (flue) gasses
Electrode
An electrical terminal that will conduct a current
Flame rectification
The process by which a flame produces a sensible electrical current
Heat exchanger
A device, usually metal, that is used to transfer heat from a warm surface or substance to a cooler surface or substance
Hot surface igniter
A ceramic device that glows when an electrical current flows through it. Used to ignite gas in a gas furnace
Induced-draft furnace
A furnace in which a motor-driven fan draws air from the surrounding area or from outdoors to support combustion
Infiltration
Air that enters a building through doors, windows, and cracks in the construction
Manometer
An instrument that measures air or gas pressure by the displacement of a column of liquid
Natural-draft furnace
A furnace in which the natural flow of air from around the furnace provides the air to support combustion
Oil burner
The main component of an oil-fired furnace. It combines oil and air and sprays the combination into the combustion chamber
Orifice
A precisely drilled hole that controls the flow of gas to the burners
Piezoelectric
The property of a quartz crystal that causes it to vibrate when a high-frequency voltage is applied to it
Primary air
Air that is pulled or propelled into combustion process along with the fuel
Redundant gas valve
A gas control containing two gas valves in series. If one fails, the other is available to shut off the gas when needed
Relative humidity
The amount of moisture in the air in relation to the capacity of the air to hold moisture
Safety pilot
A pilot light with a flame-sensing element
Secondary air
Air that is added to the mix of fuel and primary air during combustion
Standing pilot
A gas pilot that is on continuously
Spud
A threaded metal device that screws into a gas manifold. It contains the orifice that meters gas to the burners
Thermocouple
A device made up of two unlike metals that generates electricity when there is a difference in temperature from one end to the other
Vaporized-type oil burners
Grade # 1 oil is used for
Pressure-type oil burners
Grade #2 oil is used for
Round chambers
70 to 90 degrees
Long chambers
30 to 60 degrees
A gas-fired warm air furnace heats by
Conduction
If you burn your finger by touching a hot surface, it is an example of
Convection
A gas burner flame should be
Blue with an orange flame
A oil burner flame should be
Yellow
Butane
Has the highest heating value
Flows over the heat exchangers
In a forced-air furnace, air
Extracts heat by condensing the flue gas that flows through the heat exchangers
In a condensing furnace, the condensing heat exchanger
Humidifiers
Add moisture to the air
Low-pressure gun type
Pressures from 1 to 15 psi
High-pressure gun type
Pressures up to 100 psi
Single-stage oil pump
Is used where the oil supply is above the burner and oil is fed by gravity
Two-stage oil pump
Used where the storage tank is below the burner
Nozzle assembly
Consists of Oil feed line, the Nozzle, Ignition electrodes, and the transformer connections
Power assembly of a high-pressure burner
Motor, fan, and oil pump