An In-Depth Explanation Of The Terms Used On The Gas Superstore

Air Vent

Means of air supply to a room (usually 100cm2) from outside air to assist the combustion process.

Balanced Flue

Either inset or outset, these fires have been designed for homes without a chimney or flue. All Balanced Flue Gas Fires are glass fronted. They vent directly outside through a horizontal co-axial pipe (one pipe within a larger pipe). The outer pipe draws air in from the outside and the inner pipe expels combustion gases. An electricity supply is not required for these products.

Class 1 Flue

A Class 1 Flue is easily recognised by a conventional brick chimney with chimney stack on the roof. This relies on the natural ´pull´ to expel the products of combustion out of the chimney pot. The minimum internal diameter for class 1 is 180mm. This allows you to have most types of fires.
Occasionally, a flue liner may have been used to rectify a leak. If this is the case the liner needs to have a minimum internal diameter of 180mm. If the liner has an internal dimension is only 127mm the chimney becomes Class 2.

Class 2 Flue Pre-Fabricated Flue

A Class 2 Pre-Fabricated Flue is a metal flue box that is situated behind the fire connecting to a series of metal flue pipes running up through the house terminating with a pipe and terminal through the roof. The internal diameter of the pipe is 127mm. There are a large number of fires available for this situation. Occasionally, the flue may have been constructed using 180mm pipe. If this is the case, the flue is classed as Class 1.

Class 2 Pre-Cast Flues

Class 2 Pre-Cast Flue are commonly found in more modern homes. Constructed using hollow concrete flue blocks which create a flue up through the property usually terminating with a ridge vent on the roof. In most cases there is usually a flat wall where ther fire goes. This does limit slightly the choice of fires suitable as depth can be an issue.

Convector gas fire
Convector gas fires give a more rapid and even heat distribution throughout the room. Convected heat occurs when a fire actively draws in cold air from the room, passes it through a heat exchanger to warm it up before sending it back out to the room as warm air.

Decorative gas fire

A gas fire designed to be installed in an open flue and to simulate a solid fuel fire. This term is also used to describe a fire that will give minimum heat output.

Fire bed

The area above a gas fire burner where the gas burns.


A frame placed in front of a fire to prevent accidental contact and used especially to protect children and elderly persons.

Flame supervision device (FSD)

A safety device that monitors a pilot and cuts off the gas supply to the main burner if the pilot is extinguished.

Flueless or Catalytic Gas Fires

These fires do not require any chimney or flue or even an outside wall – they use the latest in gas fire technology and can be installed virtually anywhere – the combustion gases produced by the fire pass through a catalytic converter within the appliance which converts the poisonous Carbon Monoxide into harmless Carbon Dioxide and water vapour.

Fret (Fire Front)

External decorative fire front usually freestanding and finished in brass, silver or black.


Simulated fuel effect of a fire such as coal, pebbles or driftwood effects.

Gas input

The amount of gas used by an appliance usually quoted in Kilowatts per hour on maximum setting.


The floor of a fireplace that extends outwards into the room.

Heat output

The typical maximum heat output of an appliance usually quoted in Kilowatts per hour.

Inset fire

An appliance that fits into a fireplace opening, no part of which projects forward of the vertical plane of the chimney breast. Designed to fit into a standard fireplace opening – these types of real flame fires are the most popular and replicate the appearance and appeal of a coal fire without the inconvenience associated with burning coal. It is suitable for installation into a traditional (Class 1) or Class 2 flue. Balanced flue and Powerflue versions on some models are also available.

Low lintel

A fireplace lintel (supporting beam) at a low level.


Liquid Petroleum Gas. Certain properties, especially in rural areas have no access to natural gas and the most common alternative is to have a LPG tank installed. Not all gas fires are compatible to work with LPG.

No-vent (NV)

A gas fire that would normally operate without additional purpose provided ventilation.

Outset Fire

This type of gas fire hangs onto the wall or sits onto a hearth. It will usually have living flames or a glass front to increase efficiency. It is suitable for installation into a traditional (Class I) or pre-cast & Class II flue. Balanced flue (no chimney or flue required) versions of some models are also available.

Oxygen Depletion Sensor (ODS)

A safety device which is part of the pilot assembly, that extinguishes the fire if there is a build up of harmful gases.

Permanent pilot

A pilot light that is left on continuously, removing the need to turn it on each time the appliance is lit.

Piezo Ignition

Most gas fires are supplied with manual piezo spark ignition which allows the user to light the fire by simply turning a control knob (usually located discreetly behind the front trim of the fire) 


A small jet of gas that is used to ignite a main gas burner.


Powerflue Gas Fires expel the flue gases directly outside the building through the use of an electronically driven fan unit mounted on the external wall.
A sophisticated microprocessor monitors performance and automatically shuts off the fire in the unlikely event of operation failure. The fan eliminates the need of a glass front. Availble on both inset and outset gas fires the Powerflue feature requires an electricity supply.

Radiant gas fire

All gas fires give off radiant heat. Radiant heat is like being warmed by the sun. The heat moves (radiates) outward from the fire into the room, the closer you get to the fire the warmer you feel.

Rear vent

A flue for a power flue fire whereby the flue exits from the rear of a fire directly through a wall to outside air.


A Fireplace Surround rebate is the difference between the outside and inside leg return. It is the distance from the face of the back panel to the wall behind. Fire Surround rebates can occasionally be increased to allow for a deeper fire in flat-wall or shallow flue situations.

Remote Control

Operational control on a gas or electric fire. This type of control is ideal for those who want the added luxury of being able to adjust their fire from the comfort of their armchair. In many instances this type of control will be available only as an extra cost option – although more and more fires are now being produced with remote control as standard.

Slide Control

Operational control on a gas fire. This type of control is ideal for those who want to be able to switch the fire on/off or up/down without having to kneel or bend down to hearth level. The control lever is located at high level on the side of the gas fire. A mechanical linkage connects from the lever to the gas control knob beneath the fire. In most instances this type of control will be available as an extra cost option.

Spacer kit

Additional accessory necessary when the depth of an opening is restricted for particular installations.


A decorative metal frame around an appliance used in conjunction with a fire front.


Means of air supply to a room (usually 100cm2) from outside air to assist the combustion process.