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Flue Liners for Stoves

Chimney Flue Liner Installation

Minster Stoves & Heating offers new and replacement chimney flue liner installation in Herefordshire & the surrounding counties.

Modifications to existing chimneys and installations of flue liners and flue systems are subject to strict local Building Regulations and legal requirements and, in the interests of safety, only appropriately qualified persons should undertake such work.

Why a good flue system is important

Providing the correct amount of flue draught or “pull” is crucial to the successful performance of a wood burning or multi-fuel stove. Flue draught helps draw air into the stove combustion chamber, removes the harmful products of combustion and disperses them to the outside air.

An average sized sitting room has a volume of air around 45 to 55 cubic metres before furniture/fittings and of course people (who also use available air for breathing!) Well insulated and draught-proofed rooms can severely limit the supply of available air within a room. It is important that Building Regulations’ guidance on air supply and ventilation is strictly complied with to ensure there is sufficient available air within a room to allow a stove to function correctly.

Hot and expanding flue gasses from your stove will be lighter than the cooler air outside (remember heat rises). This effect produces a difference in pressure between outside air and flue gasses and helps create up-draught. Taller flues usually provide even better draught. As mentioned elsewhere on our website, keeping flue gasses as hot as possible, for as long as possible will aid flue up-draught. However, getting the flue height correct is important, taller is not always better as all flue gasses cool as they rise, taller chimneys can result in quicker cooling and thus reduced up-draught.

Chimneys built before 1965 usually have rough inner surfaces with possibly bends and voids, this can cause resistance to the natural flow of flue gasses resulting in slow movement and cooling. Chimneys built after 1965 are often clay or concrete lined. Once again these are not ideal for stoves as the cement joints between sections cannot be guaranteed to be complete simply because they are hidden from view and there is no guarantee the bricklayer sealed the joints fully or correctly.

Over a period of time, the intense heat generated and cooling cycles together with chemical reactions from condensates and flue gasses can cause damage to chimneys leading to potential leaks (and possibly dangerous carbon monoxide leakage). Additionally leakage can cause a slowdown in draught or very cool flue gasses and ultimately the performance of the stove will be affected.

Chimneys that appear to operate well with open fires may not always work efficiently with a stove. Unlike open fires, flue gasses from stoves reach much higher temperatures and this could affect the safety and performance of the chimney.

Flue Liner Advantages

Fitting a HETAS approved solid fuel stainless steel flexible liner to an existing chimney will improve the safety and performance of your stove installation; therefore, professional stove installers will always suggest the use of a flue liner.

One of the advantages of flue liners is that they provide some insulation which will help to maintain the temperature of flue gasses; hot flue gasses create a better flue draught. This is especially noticeable where a chimney is on an outside wall (rather than in the centre of a home). Chimneys located on outside walls are subject to wind chill.

Using a flue liner within a chimney also helps protect wall covering and paint finishes on the chimney breast from damage from tar and condensates.

With boiler stoves, fitting a flue liner is ESSENTIAL. Boiler stoves operate at much lower temperatures than wood burners or multi-fuel stoves. With boiler stoves, the boiler inside the stove draws heat from the stove fire chamber to heat the water in the boiler. Therefore, flue gasses passing up the chimney are significantly cooler. Cooler flue gasses reduce the effectiveness of the up-draught and the gasses rise much slower, cooling even more as they rise. One of the problems with cool flue gasses are smoky chimneys, soot deposits (which require chimney sweeping more frequently) and creosote problems.

Reasons to fit a liner in a chimney

  • The existing chimney causes smoke and potentially dangerous fumes to enter the house.
  • The existing chimney void size is not compatible with the stove manufacturer’s flue outlet specification (see Building Regulations Document J) and needs to be reduced by the installation of a flexi liner to maximise the stove’s performance.
  • The existing clay or concrete liner has poor joint seals causing condensates to run outside the liner rather than inside the liner, thus increasing the likelihood of staining.
  • Porous brickwork, weak mortar joints and condensates have caused unsightly staining on the interior or exterior of the chimney breasts/walls.
  • The chimney is ‘cold’, usually because it features a large void, is on an outside wall or is subject to strong prevailing winds, any of which will make it very slow to ‘warm’ and difficult to create the critical up-draught that a stove needs to burn efficiently and safely.

With all of the above in mind it is obvious to see why, in our opinion, a flue-lined chimney will always provide the best option.