Gas fires are grouped by how they get rid of their fumes. A conventional flue fire uses a chimney or flue; a balanced flue fire is sealed from the room and vents through an outside wall; a power flue fire uses a fan to do the same; and a flueless fire cleans its combustion products with a catalytic converter and needs no flue, but must have a minimum room size and a permanent air vent.
Which you can have depends on your flue, so this guide starts there. It then compares real fires from the Ekofires range, covers efficiency, ventilation, safety and the law, and ends with a simple way to choose. Every gas fire must be fitted by a Gas Safe registered engineer.
The main types
| Type | Needs | Pros | Watch-outs |
|---|---|---|---|
| Conventional flue, open-fronted | A chimney or flue suited to the fire | Widest choice of styles and fuel beds; a real open flame | Loses more heat up the flue |
| High efficiency glass-fronted | A chimney or flue suited to the fire | Much higher efficiency | The flame is behind glass |
| Balanced flue | An outside wall behind or near the fire | No chimney needed; sealed from the room | Terminal position rules on the outside wall |
| Power flue | An outside wall within reach of a fan-assisted duct | Works where a balanced flue cannot | Fan noise and electrical supply |
| Flueless (catalytic) | Minimum room size and a permanent vent | No flue needed; suits most rooms with a gas supply, but not bathrooms | Low output; often not a primary heat source |
Brick chimney or Class 2 flue
Full depth open fires
The traditional look, with a deep fuel bed and a real open flame.
Shallow and pre-cast flues
Slimline fires
Shallow fireboxes for pre-cast flues in newer houses, and conventional chimneys too.
Lower running costs
Glass-fronted fires
Sealed behind glass for far higher efficiency than an open-fronted fire.
No chimney at all
Flueless fires and stoves
Catalytic fires that need a minimum room size and a 100cm² vent, but no flue.
Conventional flue fires and your flue class
- Class 1: a traditional brick or stone chimney, usually at least 175mm (7 inches) across, with a chimney pot or gas terminal on top. Suits almost any conventional flue fire, including full depth and decorative fuel effect fires.
- Class 2: a prefabricated metal flue, usually 125mm (5 inches), with a metal cowl or terminal on the roof.
- Pre-cast flue: rectangular interlocking blocks built into the wall, typically with a ridge vent on the roof. Shallow, so it needs a slimline fire designed for pre-cast flues.
Approved Document J sets minimum flue sizes: a radiant or convector gas fire needs a 125mm circular flue (or an equivalent rectangular flue), and inset live fuel effect and decorative fuel effect fires in a fireplace opening up to 500mm x 550mm need a minimum flue dimension of 175mm, although some are approved for 125mm. Gas fires may be installed in fireplaces with flues built for solid fuel, provided the combination is shown to be safe in the manufacturer's instructions.
The depth of your fireplace opening matters too. Full depth fires need a deep opening: the Ekofires 3060 has an inset depth of 250mm. Slimline fires need far less: the 3010 and 3015 fireboxes are 108mm deep, and the glass-fronted 4010 HE is 125mm.
Not sure which flue you have? Our guide to chimney and flue options shows how to tell.
Examples from the Ekofires range
| Fire | Type | Heat output | Efficiency | Flue or room needs |
|---|---|---|---|---|
| Ekofires 3060 | Full depth, open-fronted convector | Up to 4.0kW (gross) | 60% | Brick chimney (Class 1) or prefabricated flue (Class 2) |
| Ekofires 3090 | Open-fronted radiant, Victorian-style fascia | Up to 3.8kW (gross) | 55% | Brick chimney (Class 1) or prefabricated flue (Class 2) |
| Ekofires 3020 | Slimline convector, open-fronted | Up to 4.1kW (gross) | 67% | See product page for approved flues |
| Ekofires 3015 | Slimline radiant, open-fronted | Up to 3.1kW (gross) | 50% | Pre-cast flue or conventional chimney |
| Ekofires 4010 HE | Slimline, glass-fronted high efficiency | Up to 4.0kW (gross) | 90% | Most flue types, including pre-cast, given enough inset depth |
| Ekofires 5510 | Flueless inset | 1.3kW to 2.3kW | Flueless | No flue; room of at least 27m³ and a 100cm² vent |
| Ekofires 5060 | Flueless, wall-mounted | 1.3kW to 2.0kW | Flueless | No flue; room of at least 23m³ and a 100cm² vent |
| Ekofires 6010 | Flueless gas stove | 1.5kW to 3.1kW | Flueless | No flue; room of at least 35m³ and a 100cm² vent |
Figures are the manufacturer's stated figures. If you would rather have the look of a stove on a flue, the Opus Trio Scala is a natural gas stove with a ceramic log effect and remote control, giving 4.3kW to 6.9kW through a 125mm top flue.
Open-fronted or glass-fronted?
The difference between 60% and 90% efficiency is large. For the same heat in the room, an open-fronted fire burns noticeably more gas than a glass-fronted high efficiency model, because more of its heat goes up the flue with the room air it draws in. If the fire is your main heat in the room, efficiency matters; if it is for occasional evenings, the look of an open flame may matter more.
Open-fronted fires come as radiant fires, which throw heat forward from the fuel bed, and convector fires, which also draw room air through a heat exchanger behind the firebox and return it warmed. The 3060 and 3020 are convectors, which is why they are more efficient than the radiant 3015 and 3090. Most Ekofires inset fires let you choose the trim, fret and fuel bed, so you can match a period or contemporary fireplace.
Efficiency is not the same as output. Output is the heat the fire gives the room. Efficiency is how much of the gas it burns becomes useful heat. Compare both when choosing.
Balanced flue and power flue fires
A balanced flue fire is room-sealed: a twin-wall pipe through the outside wall brings in combustion air and takes fumes out, so the fire uses no room air and needs no chimney. They are usually glass-fronted, so they tend to be efficient as well. A power flue fire uses a fan to push fumes out through the wall and can sit further from it. Both need an outside wall where the terminal can meet the clearance rules from windows, doors and boundaries, and a power flue needs an electrical supply for the fan.
Flueless gas fires
A flueless fire burns gas cleanly and passes the combustion products through a catalytic converter, which turns carbon monoxide and unburnt gas into carbon dioxide and water vapour. Nothing is vented outside, so every bit of heat stays in the room, but the room must be large enough and must have a permanent vent: typically 100cm², with a minimum room volume set by the manufacturer. Outputs are low (around 1.3kW to 3kW) and manufacturers often say they are not for use as a primary heat source. Expect some condensation in a small or poorly ventilated room.
Ventilation for flued gas fires
Under Approved Document J, a decorative fuel effect gas fire in a fireplace with a throat normally needs a permanent air vent of at least 100cm². In homes with an air permeability above 5.0 m³/(h.m²), a vent may not be needed for decorative fuel effect fires rated no more than 7kW (net) with a flue gas clearance rate of no more than 70 m³ per hour. Other flued fires follow the manufacturer's instructions and Approved Document J; the Ekofires 3060 and 3090, for example, are listed as not needing an air vent, which holds in most older homes; in an airtight home (5.0 m³/(h.m²) or less) Approved Document J asks for 500mm² of permanent vent per kW of an open-flued fire's net heat input. Your Gas Safe engineer will check this. For stoves and open fires, see do I need a vent?
Safety and the law
- Gas Safe only. By law, anyone paid to work on gas in your home must be on the Gas Safe Register, and anyone doing gas work must be competent, so always use a registered engineer. Check the back of their ID card to see they are qualified for gas fires.
- CO alarm. Since 1 October 2022, Building Regulations in England require a carbon monoxide alarm in the room when a new or replacement fixed gas appliance, other than a cooker, is installed in a home.
- Annual service. Have gas fires serviced and safety checked every year.
- Built-in safety. Ekofires inset fires such as the 3015, 3020, 3060 and 3090 have an oxygen depletion sensor and a flame failure device, which shut the gas off if something is wrong.
- Natural gas or LPG. Check the fire's data plate. Many fires, including all of the Ekofires inset models above, are natural gas only; the 5010 and 5060 wall-mounted flueless models are also made for LPG.
Smell gas? Do not use switches or flames, open doors and windows, turn off the gas at the meter if you can, leave the property and call the National Gas Emergency Service on 0800 111 999 (0800 002 001 in Northern Ireland).
Which gas fire should you choose?
- Brick chimney, want a traditional look: a full depth fire such as the Ekofires 3060, or the Victorian-style 3090.
- Pre-cast flue: a slimline model designed for it, such as the 3015 or 4010 HE; see slimline gas fires.
- Want lower running costs from a flued fire: a glass-fronted high efficiency fire.
- Want a period fireplace: a cast iron fireplace with its matching gas fire; see choosing a cast iron period fireplace.
- No chimney: balanced flue, power flue or a flueless fire.
See all inset gas fires and gas fires and stoves.
Common questions
What is the difference between a flued and flueless gas fire?
A flued fire sends its fumes outside through a chimney, flue or wall terminal. A flueless fire cleans them with a catalytic converter and needs no flue, but must have a minimum room size and a permanent vent.
Which is more efficient, open-fronted or glass-fronted?
Glass-fronted. For example, the Ekofires 4010 HE glass-fronted fire has a stated efficiency of 90%, against 60% for the open-fronted 3060.
Do I need a vent for a gas fire?
It depends on the type. A decorative fuel effect fire in a fireplace with a throat normally needs 100cm². Flueless fires need the vent the manufacturer specifies, typically 100cm². Your Gas Safe engineer will confirm.
Do I need a carbon monoxide alarm with a gas fire?
Yes. For new or replacement installations, Building Regulations have required one in the same room in England since 1 October 2022 and in Wales since 6 January 2025. Scotland and Northern Ireland have their own requirements.
Can a flueless gas fire heat a whole room?
Usually only as supplementary heat. Outputs are low, around 1.3kW to 3kW, and manufacturers often say flueless models are not suitable as a primary heat source.
What is a pre-cast flue?
A flue made of interlocking concrete blocks built into the wall, common in houses from the 1960s onwards, usually with a ridge vent on the roof. It is shallow, so it needs a slimline fire approved for pre-cast flues.
Can I fit a gas fire myself?
No. The law requires anyone doing gas work to be competent, and anyone paid to do it to be Gas Safe registered. Use a Gas Safe registered engineer, who will also test the flue and check the ventilation.
Can I add a remote control to my gas fire?
On some models. The Ekofires 3010 can take an optional mains-free remote that adjusts the flame height once the pilot is lit, and the 3020 is available with remote control for natural gas.
Find the right gas fire
Tell us your flue type and the size of your fireplace opening, and we will help you choose a fire that fits and suits the room.
