Five ways to tell what kind of chimney you have.

Balanced flue fire

Is your chimney type here?

Your choice of gas fire or other heating appliance in the UK will be determined by the type of chimney or flue in your home, if there is one at all.

You will be able to identify which flue type you have by observation, or by asking your local specialist independent fireplace retailer to advise you. Let’s try observation first.

1. If you have a chimney breast in your home and a brick chimney on your roof, it is likely that you have a ‘Class 1’ chimney which should be suitable for burning wood, solid fuel or
gas in your fireplace or stove. Class 1 chimneys are usually constructed of brick or lined with clay liners, but can also be made of pre-cast sections in heat-resistant materials or even twin-wall insulated stainless steel sections. Class 1 chimneys must be a minimum of 175mm/7″ internal diameter. A chimney should be swept and inspected by a registered chimney sweep or other expert before being brought back into use. If a chimney is found to be unsound, it may have to be lined before it can be used. Using a flexible stainless steel flue liner is the generally accepted method for cost-effectively making good, but other methods are also available. If the chimney has already been lined, it will be important to establish the size (diameter) of the liner to decide which appliances may work with the liner. It will probably be 125mm/5″ or 200mm/8″. You will also need to establish the type of terminal that has been fitted, by observing from outside.

2. If you have no chimney breast but there is a shallow fireplace opening built into the wall in your living room, it is likely that you have a pre-cast flue. This is a letter-box sized flue that is built into the cavity wall construction as the house is being built and is only suitable for use with appropriately designed gas fires. Other identifiers of a pre-cast flue would be the roof vent or terminal, either a perforated ridge tile or possibly a small diameter (125mm/5″) stainless steel flue and terminal which protrudes vertically from the roof tiles. If there is already a suitable gas fire installed, it will inevitably be distinguished by its shallow fuel bed.

3. Some homes have been built with what may appear to be a Class 1 chimney breast, but may be found to only have a small diameter (125mm/5″) factory-made metal flue installed, which will reduce the choice of gas fires that may be used, although any ‘Class 2’ approved gas fire should be capable of working safely in such a situation. The on-roof identifiers are similar to pre-cast flues in ‘2’ above. Such Class 2 flues are only suitable for use with appropriately designed and approved gas fires.

4. If there is a gas fire installed in your room and there is no apparent chimney or flue as described above, you may have a powerflue fire or a flueless fire. A powerflue gas fire uses a fan built into a simple flue duct, usually on the back of the fire, which must be fitted to an outside wall. The fan itself will protrude partly or wholly from the wall on the outside of the house and will be easily visible, as an identifier. These fires must be connected to mains electricity in order to work and the tell-tale fan noise is a another good identifier. In the last ten years, innovative gas fires which do not require a flue at all (flueless fires) have come onto the market and the best ones have built-in catalytic converters which safely remove carbon monoxide from the products of combustion. With this type of fire there are minimum room ventilation requirements, usually a 100cm2 airbrick is required to be installed and it is recommended that another heat source such as central or underfloor heating is also present in the room.

5. Another, more up to date and energy-efficient option for houses without flues or chimneys, is the balanced flue gas fire. These fires are designed to exhaust the flue gases through a simple twin-wall factory-made flue sections which can be installed virtually anywhere in a home. An outside wall is not a necessary requirement. The flue can exit either vertically or horizontally from the house, giving a multitude of installation options. No additional room ventilation is required as balanced flue fires are room-sealed and use outside air (for combustion) which is drawn into the combustion area through the concentric construction of the flue itself. Balanced flue fires are typically high-efficiency, glass-fronted appliances and many are at the forefront of the fashionable, minimalist look that so many people aspire to in today’s fashion-conscious world. Balanced flue fires can be identified by the flue terminal, which most often protrudes from an outside wall but may also be installed in a vertical situation.

An expert should always be requested for advice before purchasing any gas or solid fuel heating appliance. Most independent fireplace retailers can offer a site visit service, prior to purchase. Woodburning stoves in particular require expert advice prior to installation.


About Urban Fires

Tony Young is a product designer and has more than 30 years of experience in the fireplace industry, amongst them the creation of several significant and innovative new decorative gas fire genres - from the Wonderfire AirFlame ceramic burner of 1984 (which remains in production at Dimplex), the award-winning 1988 Vermont Castings Intrepid gas stove, another UK award-winner the Galaxy Roxy, the Next Design Neon and Brilliant Fires Storm designs, plus multiple award-winners, the current Acquisitions X-FIRES flueless fires range. He writes for industry magazines.
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2 Responses to Five ways to tell what kind of chimney you have.

  1. A good an interesting article.
    Thanks for the info.

  2. Pingback: Five reasons why developers should always install fireplaces in higher value homes. | urbanfires

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