Flue Lining Facts: Essential or a Costly Waste of Time?

 

Some flue lining and liner background… including a few misunderstandings!

Since around 1965 it has been law (building regulations) that a chimney should be lined in England and Wales. This is with a material impervious to flue gases and condensation such as concrete, clay or stainless steel.

This was nothing to do with stoves, it was simply to stop flue gases and moisture from eroding the masonry and leaking out of the flue structure and as most liners were 9” or above these liners usually supported open fires, not modern efficient stoves.

“I have been told that I don’t have to have a flue liner.”

If your chimney is already lined (say with clay or concrete) then legally, as long as your flue is sound then this is right. However, fitting a liner with a stove is not just about the legal question it’s as much to do with the performance and maintainability of your stove.

Say your open fire is about 10% efficient, and a stove is 80% efficient.  This is directly related to how much hot flue gases are produced. The stove by design, exhausts far less hot flue gases than an open fire. For a flue to work correctly the temperature inside the flue must be hotter than outside the flue.

If the flue lining does not get hot then you risk excessive condensation (creating creosote) and a poor draw. A flue liner sets the size of the flue ideally for the stove. Years ago we used to design and make stainless steel adapters between fireplaces with clay or concrete liners and stoves to save fitting a liner but allow the flue to be swept through the stove – they never last!  Sooner or later they will leak creosote or come adrift, they not a good solution unless there is no other choice.

If your clay liner is 9” and your stove pipe is 5” without removing the stove its not possible to sweep the flue properly. Some large old chimneys designed to pull on a large open fire can pull so hard that it is not possible to control the stove properly, a liner helps to correct this.

In the end,  the informed advice is that you are wasting your time and money buying a good stove and fitting it without a good quality liner.

Are all flexible liners the same ?

Flue liners vary in quality, material and application. How many times have we been told by a confident builder that “ I do it myself, I fit a Copex liner” – Copex is a brand name not a type and generally they are fitting the less expensive gas version to a solid fuel appliance which is dangerous!

Generally there is 316 grade and 904 grades both are classed as having two walls, smooth inside and corrugated on the outside. 316 is a good general purpose liner suitable for wood and medium to light use where as the 904 grade is better for heavy use with more coal based products.

One of the key areas which effects flue quality is the overlap of the stainless steel foil which creates the inner skin and outer skin. The cheaper brands overlap the foil less and so use less expensive stainless steel foil – the down side is that these inferior offerings leak when bent around a corner. They tend to come apart when pulling down the chimney as the crimping is less substantial.

The quality of the manufacture varies enormously, we have tried endless manufacturers over the years before arriving at our current choices not surprisingly, none of them are the cheaper “budget internet” brands.

 

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