| A | B |
|---|
| 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 the 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 the 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. |
