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Gas Fire Fact Sheet

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The aim of this Fact Sheet is to assist installers, specifiers and purchasers of domestic heating by providing guidance on selecting a gas fire to:

  • Improve energy efficiency,
  • Reduce running costs,
  • Reduce emissions of carbon dioxide (CO2)
  • Be the most suitable for the type of dwelling where it is to be installed


While central heating is the most widely-used way to heat houses in the UK, using an individual space heater such as a modern gas fire can also contribute to the efficient, economical heating of your home.

A modern, efficient gas fire will:

  • Provide economical heating at any time, directly where you want it.
  • Be particularly effective when you don’t want to turn on the whole central heating system or when you want to warm a single room quickly – for example when you come in on an unexpected chilly evening.
  • Provide an important “focus” for your living room – but having an attractive fire does not have to mean low energy efficiency and high carbon emissions. Modern technology means that very efficient gas fires, with high “flame effect” visual appeal, are now readily available.

Key Points

  • Ease of upgrade – Replacement of an existing, less efficient, older gas fire is easy – modern efficient gas fires are compatible with existing flues and chimneys or even where there is no chimney at all.
  • Modern high efficiency – There are a number of different types of modern gas fire – not all of which have the same efficiency and features. It is important to consider the right type of gas fire for your needs – see Table 2 below.
  • Cost savings – replacing an old gas fire with a new, high-efficiency unit can offer significant savings per annum depending on the fire you choose – see Table 1 below.
  • Relative cost vs other fuel types – Gas costs less per kWh than heating oil, LPG, electricity and, in most cases, wood. Although anthracite and bituminous coal are cheaper, the emissions from these fuels are the highest of the fuel types.
  • Relatively low CO2 Emissions – Gas generates less carbon per purchased kW/hr than economy electric, heating oil, anthracite and bituminous coal. It is second only to logs and wood pellets. You can improve your carbon emission rate considerably depending on the fire you choose – see Table 1 below.
  • Safety Features – Gas fires installed before 1997 may not have the important safety features used on modern gas fires – designed to safely shut down the gas fire if there is a severe reduction in the oxygen level in the room where the fire is installed. NB. This reduction in oxygen could occur if the ventilation to the room is blocked or the flue or if the chimney becomes blocked, allowing combustion products to escape into the room.
  • Aesthetics – costs savings, higher efficiency and ease of installation does not mean compromising on the look of your house. There are many choices of fires to complement your décor and meet to your specific requirements.


Gas fires are not as efficient as a gas central heating system.

As Table 3 shows, you can have gas fires that are very efficient and, with the ability to easily control their output to suit your immediate requirements (e.g. switching on the fire “just to take the chill off the room”), you will not be using unnecessary heat in the rest of your house.

I don’t need a gas fire if I have a central heating system.

A gas fire gives the ability to quickly heat a specific room (or area) in the house. This may be a more efficient way to heat your home in the autumn and spring, when full central heating is not always required.

Electric fires are more efficient than gas fires.

Although an electric fire has a higher “point of use efficiency”, when the inefficiencies of electricity generation and energy lost during transmission to the property are taken into account, an efficient gas fire is more efficient and more environmentally friendly. This overall benefit in efficiency is recognised in government energy efficiency (SAP) calculations involving electric and gas fires.

I don’t have a chimney, so I can’t have a gas fire

There are types of gas fire (e.g. a flueless gas fire, a balanced flue fire or a powered flue fire) which do not require a chimney.

Jargon-Busting (some key definitions)

Gas stove:
A gas fire designed to have the appearance of a wood or coal-burning stove.

Heat exchanger:
A device built into some gas fire types which takes heat from the flue gases and transfers it to the room air, while keeping the two separate so that combustion products do not enter the room

Slimline gas fire:
Otherwise known as an “inset” gas fire, the fire is designed to be fully or partially recessed into the chimney breast or wall (often referred to as the builder’s opening) to minimise projection into the room.


Most older properties were built with a chimney to take the smoke from an open coal fire, along with other combustion products, out of the room and into the outside air. An existing chimney is often used to take away combustion products when a gas fire is installed in place of the coal fire.

Most modern properties were (and still are) built with purpose-designed flue ducts, perhaps concrete or metal-lined, to be used when the builder or the home-owner installs a gas fire.

Where modern properties are designed with no flue or chimney, the use of a flueless, balanced flue or powered flue fire can be particularly effective.

See Table 3 Chimney/Flue Types for further information.


 (Please note that these questions and answers are for guidance only)

What type of gas fire can I have in my home?

The type of chimney or flue you have usually dictates your choice of fire. Look at Table 3 (Chimneys and Flues Types) for further guidance.

How do I tell what type of gas fire I have now?

A competent gas installer should be able to advise on this, however as a guide to identifying the type of fire you have –

(a) If the gas fire consists of a free-standing “bed” of simulated coals or logs, located in an open fireplace which has no obvious restrictions in the chimney or flue then it is likely to be a “decorative fuel effect appliance” (see Table 3) . The fire draws warm air from the room out through the chimney and thus causes some heat loss. This type of fire has a relatively low efficiency and is intended for decorative purposes only.

(b) If the fire has an open bed of simulated coals or logs, with a surround or case which is inset into the fireplace (or projects slightly from it) and which restricts the fireplace opening then it is likely to be an open fronted convector fire. This appliance will already be of moderate efficiency as more heat is circulated into the room via convection (see Table 3)

(c) If the fire has an array of white ceramic elements which glow red once the fire is operating then it is a radiant convector fire. This type of fire will have moderate to high efficiency.

(d) If the fire has a bed of simulated coals or logs behind a glass front, with the fire itself either set into or standing out from the chimney or flue opening then it is likely that this is a glass fronted convector fire of moderate to high efficiency.

(e) If the fire does not use a chimney or flue, but has a glass front and discharges the heat through a catalytic converter directly into the room, then it is likely that this is a flueless fire of high efficiency.

Are all gas fires equally efficient?

No, they are not. See Table 1.

How do I find out the efficiency of a new gas fire?

A reputable gas fire manufacturer will publish the gas fire efficiency in their product literature, in the appliance instructions, or on their company website with the appliance description. Both gross and net figures can be quoted, however government efficiency calculations use the gross figure.

Can I fit a gas fire myself?

A gas fire must be fitted by a competent person, such as a Gas Safe-registered installer. Registered installers can be found in your local press, Yellow Pages, or via the “find an installer” facility on this website.

Where can I buy a new gas fire?

Gas fires can be purchased from a wide variety of outlets including specialist fire/fireplace suppliers and showrooms (look in local press or Yellow Pages), and from major “high street” retail chains. Useful advice on where to buy can also be obtained from qualified and experienced installers.

I haven’t got a chimney or flue. Can I still have a gas fire?

Balanced-flue, powered flue and flueless gas fires don’t need an existing chimney or flue.

For balanced-flue and powered flue gas fires, providing you have an outside wall suitable to mount the fire or heater onto, and a gas supply, you’re away. For balanced-flue fires, a small hole through an outside wall takes care of the flue. Because these fires are room-sealed they are glass fronted and can sit on a hearth or be inset. However, if you prefer an open-fronted fire then choose a powered flue gas fire, a complete system which can be inset into a wall or surround.

For a flueless gas fire you don’t even need an outside wall, however there are certain provisions that must be adhered to:

  • A purpose made air vent of a size recommended by the fire manufacturer must be installed,
  • The fire must not be the sole source of heat in a room, it is designed to be supplementary to central heating as insufficient ventilation or background heat could cause condensation to form on colder surfaces.

What type of fire should I choose?

Look at the way you live your life. If the fire or stove is to be the main source of heat in the room it will need to be as efficient as possible. Or perhaps you’ve just decorated your home and need a high class flame-effect fire or a new gas stove to add that finishing touch, but still need to consider efficiency.

Remember who uses the room: if you have young children toddling around, maybe a glass-fronted fire, with a proper guard fitted in front, is the best option. If you don’t have a mains gas supply, an LPG fire may be an option.

What if I don’t have mains gas?

No problem! There are gas fires that can be easily adapted to run on Liquefied Petroleum Gas (LPG), a gas that is just as effective as natural gas. LPG is supplied in bottles or in a storage tank, which will be sited in your garden and filled from time to time by a local supplier.

Can I have a gas fire without a hearth?

You don’t have to have the ‘trimmings’ of an elaborate hearth or mantel. There are glass fronted and wall-mounted fires which are ideal for more modern homes, or when space is at a premium.

Do any fires still allow the fitting of back boilers?

Yes, there are a small number of gas fires which are designed to work in conjunction with a back boiler.

I love having a real flame gas fire but I’m disabled or am finding it more difficult to kneel down and turn it on, any ideas?

There are many fire models which feature easy-to-reach controls. Alternatively, models are available with ‘remote controls’ which use a hand held controller. So you don’t have to bend or kneel to operate your fire.

Can I convert my LPG fire or stove back to Natural Gas (or vice versa)?

It depends on the type and age of your fire. Kits are not always available and the cost maybe prohibitive. We recommend you consider a new fire, manufactured and tested specifically for Natural Gas or LPG

What is the difference between ‘outset’ and ‘inset’ fires?

Outset fires sit on the hearth outside the fireplace opening. Inset fires (sometimes referred to as “slimline” fires) sit inside the fireplace opening, behind the hearth.

What is the difference between radiated and convected heat and their ratio?

Radiated heat comes from the gas flame as it passes through the radiant elements, ceramic coals, pebbles or logs of the gas fire. These absorb the heat from the gas flame radiating infra-red heat into the room.

Convected heat is obtained from room air which is drawn behind the “firebox”, which contains the radiant elements or fuel bed of the fire, and is then passed over a heat exchanger before returning into the room. The heat exchanger is heated by the hot flue products as they pass out of the fire on their way to the flue or chimney. The heated room air is always kept separate from the flue products.

The ratio of radiant heat and convected heat varies according to the type and model of fire. To obtain convected heat the fire must have a built in heat exchanger.

What type of flue liner do I need?

If your flue needs to be replaced or re-lined then flexible flue liners must conform to BS 1856-2. Please consult your installer and read the manufacturers installation instructions before proceeding.

Which fires suit a pre-cast flue?

A wide range of fires are generally suitable for pre-cast flues. Please consult your retailer or the sales information leaflet as to the suitability of your chosen model.

Do I have to have my chimney lined?

Appliances suitable for a Class 1 flue do not normally require the flue to be lined. However the flue should be swept, inspected and tested for leaks prior to installation. If the condition of flue is very poor then it will need to be lined.

My chimney is in very poor condition and is uneconomic to repair. Can I still have a gas fire?

In this situation the chimney can be sealed (this work should be carried out by a competent person) and a balanced flue, powered flue or flueless fire can then be fitted.


Requirements for gas fires (gas-fired independent space heating appliances) in relation to Building Regulations are described in the Domestic Heating Compliance Guide (Compliance with Approved Documents L1A: New Dwellings and L1B: Existing Dwellings).

Requirements for ventilation and flues are described in Approved Document J (Combustion Appliances and Fuel Storage Systems).

Table 1.


Typical carbon and financial savings from replacing your existing decorative gas fire.


Fire Type

Equivalent Efficiency (re-based to balanced flue using SAP 2005)

Efficiency rating above decorative fire.

Carbon emission rate improvement Kg p.a.

Carbon Emissions Improvement %

Savings p.a.

Cost Improvement %

Decorative Gas Fire







(A) Open fronted convector gas fire







(B) Glass fronted convector gas fire or stove (conventional flue)









(C) Glass fronted convector fire or stove with heat exchanger (conventional flue)







(D) Glass fronted convector fire or stove (room sealed)







(E) Flueless fire












  • See section on Different Technologies for further explanation of above gas fire types.
  • Fires (A), (B) & (C) do not require additional ventilation if the input is under 7kW, and Fire Type (D) requires no additional ventilation because, as the description implies, the fire does not take air from the room in which it is installed, it takes it directly from outside the property.
  • Type (E) fires require additional permanent ventilation, for example the installation of a small air vent as per manufacturer's instructions, and minimum room sizes as specified by the manufacturer's instructions.
  • The Carbon emission rate improvement is based on the emission factor for mains gas in Table 12 in the Government's Standard Assessment Procedure for the Energy Rating of Dwellings.
  • The savings p.a. are based on 6 months use of the fire for 2 hrs per day at a gas cost of £0.042/kWh assuming that the heat output into the room remains constant between the different efficiencies quoted.


Table 2.




Efficiency Level


Heating Category


Gas Fire Type






80% plus



Primary or Secondary Heating

Balanced Flue fire or stove

  • Highly efficient energy using appliances.
  • Room sealed
  • No ventilation required.
  • No conventional fireplace or chimney/flue required.

Outside wall or roof required for flue terminal


Primary or Secondary Heating

Glass fronted fire or stove with heat exchanger. 


Conventionally flued.

  • Highly efficient energy using appliance.
  • No additional ventilation normally required for appliances under 7kW.
  • Uses existing chimneys and flues of many types.

Requires a chimney or flue.


Secondary Heating Only

Flueless  fire or stove

  • Highly efficient energy using appliance.
  • No flue or chimney or outside wall required.

Supplementary ventilation required, (e.g. a small air vent, as per manufacturer's instructions) through outside wall directly into the room.


Supplementary to primary heating.


Room size restrictions apply.


Primary or Secondary Heating

Glass fronted fire or stove.


Conventionally flued.

  • Efficient energy using appliance.
  • No additional ventilation normally required for appliances under 7kW.
  • Uses existing chimneys and flues of many types.

Requires a chimney or flue.



Primary or Secondary Heating

Open fronted convector fire

  • Moderately efficient energy using appliance.
  • No additional ventilation normally required for appliances under 7kW.
  • Uses existing chimneys and flues of many types.

Requires a chimney or flue.



Decorative effect only

Open fronted decorative fire with unrestricted flue

  • Not a heating appliance
  • Designed for visual appeal only
  • Uses existing chimney

Class 1 (solid fuel) chimney required


Normally requires additional ventilation

Table 3.



To help you understand which fires are suitable for your home we have prepared a key to classify your chimney - outlined below.


Brick Built Chimney

Brick Built Chimney


The classic brick built chimney is suitable for all gas fires and stoves. As these chimneys are deep you can choose a full depth gas fire through to the shallower slimline products.

Pre-fabricated Flue

Pre-fabricated Flue


Pre-fabricated chimneys are suitable for most gas fires and gas stoves. Pre-fabricated chimneys offer a good depth so you can choose from the majority of full depth gas fires and all slimline gas fires.

Pre-cast Flue

Pre-cast Flue


Pre-cast chimneys are found in most modern homes and suitable for a wide range of slimline gas fires and stoves. Full depth gas fires can also be used with pre-cast flues with the aid of a spacer kit. Ask your retailer or installer for more details.

No Chimney or Flue

No Chimney or Flue


No Chimney or Flue? There is still a wide range of gas fires suitable for your home - such as balanced flue, powered flue or flueless fires. (NB these can also be used in homes with all chimney types shown above).



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