Air Shutter. An adjustable device for varying the size of the air inlet or inlets regulating primary or secondary air.

Boiler. See NFPA 85, subsection 3.3.20.

Breeching. (See Chimney Connector.)

Burner. A device for the final conveyance of the gas, or a mixture of gas and air to the combustion zone.

1. (a) Injection (Bunsen) Type Burner. A burner employing the energy of a jet of gas to inject air for combustion into the burner and mix it with the gas. (b)Atmospheric Injection Type Burner. A burner in which the air at atmospheric pressure is injected into the burner by a jet of gas. (c)Luminous or Yellow Flame Burner. A burner in which secondary air only is depended on for combustion of the gas.
2. (d) Power Burner. A burner in which either gas or air or both are supplied at pressures exceeding, for gas, the line pressure and, for air, atmospheric pressure; this added pressure being applied at the burner. A burner for which air for combustion is supplied by a fan ahead of the appliance is commonly designated as a forced draft burner.
3. (e) Premixing Burner. A power burner in which all or nearly all of the air for combustion is mixed with the gas as primary air.
4. (f) Induced Draft Burner. A burner which depends on the draft induced by a fan beyond the appliance for its proper operation.
5. (g) Pressure Burner. A burner which is supplied with an air-gas mixture under pressure (typically from 0.5 to 14.0 inches of water and occasionally higher).

Burner Head. That portion of a burner beyond the outlet end of the mixer tube which contains the ports.

Burner, Automatically Lighted. One where fuel to the main burner is normally turned on and ignited automatically.

Burner, Manually Lighted. One where fuel to the main burner is turned on only by hand and ignited under supervision.

Chimney. A vertical shaft enclosing one or more flues for conveying flue gases to the outside atmosphere.

1. (a) Factory-built Chimney. A listed chimney.
2. (b) Masonry Chimney. A chimney of solid masonry units, bricks, stones, listed masonry chimney units or reinforced concrete, lined with suitable flue liners.
3. (c) Metal Chimney. A field-constructed chimney of metal.

Chimney Connector. The pipe which connects a fuel-burning appliance to a chimney.

Combustion. The rapid oxidation of fuel gases accompanied by the production of heat or heat and light.

Combustion Control. A control which automatically regulates the firing rate at predetermined air-fuel ratios in accordance with load demand.

1. (a) High-low Firing. The action of a combustion control which positions the air and fuel supply for low-fire and for high-fire in accordance with load demand.
2. (b) Modulating. The action of a combustion control which gradually varies the air and fuel supplies within limits in accordance with load demand.

Combustion (Input) Control Valve. An automatic gas-control valve for regulating equipment input.

Combustion Products. Constituents resulting from the combustion of a fuel gas with the oxygen of the air, including the inerts, but excluding excess air.

Condensate. The liquid which separates from a gas (including flue gases) due to a reduction in temperature.

Controls. Devices designed to regulate gas, air, water or electrical supply equipment. These may be manual, semi-manual, semi-automatic or automatic.

Control, Limit. An automatic control responsive to changes in liquid level; in fuel, steam or air pressure; in air, gas or liquid flow; or in temperature; for limiting the operation of the controlled equipment.

Control, Primary Safety. A control responsive directly to flame properties; sensing the presence of flame and causing fuel to be shut off in the event of ignition or flame failure requiring manual reset.

Control, Safety. Automatic controls and interlocks (including relays, switches, and other auxiliary equipment used in conjunction therewith to form a safety control system which are intended to prevent unsafe operation of the controlled equipment).

Damper. A valve or plate for controlling draft or flow of the flue gases. A damper is generally considered as being located on the downstream side or the combustion chamber usually in a flue passage of the appliance or in the chimney or vent connector.

Damper, Automatically Operated. A damper operated by an automatic control.

Damper, Manually Operated. An adjustable damper manually set and locked in the desired position.

Draft Regulator, Barometric. A device which functions to maintain a desired draft in the appliance by automatically reducing the chimney draft to the desired value.

Equipment. Any gas utilization equipment having inputs of more then 400,000 BTU's per hour per combustion chamber. This includes, but is not limited to, steam boilers, hot water boilers, water heaters, generators, and other similar gas utilization equipment.

Flame Safeguard. (See Control, Primary Safety.)

Flue Gases. Products of combustion and excess air.

Interlock. A device to prove the physical state of a required condition, and to furnish that proof to the primary safety control circuit.

Labeled. Equipment or materials to which has been attached a label of a nationally recognized testing laboratory that maintains periodic inspection of production of labeled equipment or materials and by whose labeling is indicated compliance with nationally recognized standards or has been tested and found safe for use in a specified manner.

Listed. Equipment or materials included in a list published by a nationally recognized testing laboratory that maintains periodic inspections of production of listed equipment or materials and whose listing states either that the equipment or material meets nationally recognized standards or has been tested and found safe for use in a specified manner.

Low-fire Start, Proven. The firing of a burner with fuel and combustion air controls interlocked in a low-fire position to provide safe operating conditions during light off.

Lubricated Plug-type Valve. A valve of the plug-and-barrel type designed for maintaining a lubricant between the bearing surfaces.

Main Burner Flame-establishing Period. The length of time the main burner flue safety shutoff valves are permitted to be open before the flame sensing device is required to supervise the main burner flame.

Optimum Air-fuel Ratio. A ratio of air to fuel going to the furnace which will provide complete combustion of the fuel with sufficient range of excess air to maintain a stable flame envelope.

Pilot. A flame which is utilized to ignite the gas at the main burner or burners.

Pilot, Continuous. A pilot that burns without turndown throughout the entire time the burner is in service, whether the main burner is firing or not.

Pilot, Expanding. A continuously burning pilot that is automatically expanded so as to reliably ignite the main burner. This pilot may be turned down at the end of the main burner flame-establishing period.

Pilot Flame-establishing Period. The length of time fuel is permitted to be delivered to a proved pilot before the flame sensing device is required to detect pilot flame.

Pilot, Intermittent. A pilot which is automatically lighted each time there is a call for heat. It burns during the entire period that the main burner is firing.

Pilot Interrupted. A pilot which is automatically lighted each time there is a call for heat. The pilot fuel is cut off automatically at the end of the main burner flame-establishing period.

Pilot, Proved. A pilot flame supervised by a primary safety control.

Purge. To free a gas conduit of air or gas, or a mixture of air or gas.

Regulator, Gas Pressure. An automatic gas pressure reducing device for the purpose of maintaining a uniform gas supply pressure.

Safety Shutdown. The action of shutting off all fuel and ignition energy to the appliance by means of a safety control or controls such that restart cannot be accomplished without manual reset.

Safety Shutoff Valve. A gas-control valve that is automatically closed by the safety control system or by an emergency device. The valve may be of the automatically or manually opened type.

Throttling. (See "Modulating" under Combustion Control.)

Trial-for-ignition Period. (See Main Burner Flame-establishing Period.)

Zero Governor. A regulating device which is normally adjusted to deliver gas at atmospheric pressure within its flow rating.