Do I Need To Insulate My Flexible Flue Liner?

There is NO Building Regulation that says you must insulate around a flexible flue liner, within a chimney stack. However building regulations do state that gases must be safely taken away from the building and by insulating your flexible flue liner, within the chimney cavity will ensure that the gases will travel directly up from the stove and out through the chimney top.

If the chimney is on an outside wall, or the stack is particularly tall, or the flue is of a large diameter then the answer to the question is probably YES ! By keeping the flue gases warm you will increase the speed of those gases escaping and help prevent condensation forming on the liner. Cooling gases can result in condensation flowing down the flexible liner and entering the stove itself. This may, over time cause damage to the flue and the stove.

A good quality Chimney Insulation is the ideal accompaniment to any flexible flue system, especially if your chimney is on an external wall. By keeping out the cold and maintaining the heat within the flue, Vermiculite Granules and FlexWrap or Rockwool Insulated Tubes will keep the hot gases rising for an efficient draw on your stove.

Vermiculite granules are supplied in a 100l bags and can be poured into the chimney cavity once the liner and register/closure plate are in place.

Please see our Vermiculite Calculator to estimate how many bags of Vermiculite you will need for your chimney. You will need to enter the dimensions of the chimney stack and the diameter of the liner you intend to use.

Vermiculite granules are only recommended if the chimney is watertight.

FlexWrap Blankets are supplied in 10m lengths for either 5-6” flexible liner or 7-8”. They are secured by Aluminium Securing Bands available in the two sizes as above.

FlexWrap is secured around the flexible liner before it is dropped down the chimney.

It is recommended that all joints are sealed using 50mm wide aluminium tape and then securing it with aluminium bands every 500mm.

The FlexWrap is 12mm thick and can withstand continuous high temperatures of up to 550°C as it is made from a non-combustible material.

This product can be cut with a Stanley knife.

Rockwool Tube insulation is available in 1000mm lengths to fit 5”, 6” and 8” flexible flue liner and is supplied as a tube. The tubes are manufactured from non-combustible rockwool which does not sustain vermin and will not encourage the growth of mould, bacteria or fungi.

They can also withstand continuous hot temperatures of up to 500°C.

It is recommended that all joints are sealed using 50mm wide aluminium tape. Each roll also comes with a self-adhesive tape which must be used for all joints.

To view Glowing Embers’ entire range of chimney insulating materials for all manner of installs, please click here…

4 thoughts on “Do I Need To Insulate My Flexible Flue Liner?”

  1. A new flexible liner is required to replace damaged one in a 2 storey terrace house where ground floor and 1st floor breasts re-instated to meet the original stack in the attic which is supported by steels. 1st floor breast unfortunately brick built against plasterboard! Can the new liner be wrapped in flexiwrap or rockwall tube instead of demolishing and rebuilding the 1st floor breast to remove the plasterboard? Perhaps only the length for the 1st floor coverage?

  2. We have had a multi fuel burner fitted into an existing fireplace which has a ceramic liner which clearly was fitted some time ago. The chimney was inspected, swept and had a camera survey which showed absolutely no problems. After the multi fuel burner had been a lite for a short while sticky black liquid started to come down the outside of the flue pipe and drip onto the top of the stove. The smell was acrid and burnt our noses and throat. The ceramic liner appears to be a five inch and we are hoping that you can tell us if there is a cure. We have chosen a multi fuel fire to try to help with gas price rises. We would be grateful for any help. Thank you.

    1. This is tar leaking down your chimney which is most typically a by-product of burning unseasoned wood or burning wood inefficiently. If the moisture content in your wood is too high then the steam this creates mixes with smoke, creating tar as it cools within your chimney. So the first port of call is to look into the fuel you are burning. If you are using wood, is it fully seasoned and has ideally no more than 15% moisture content? Also, are you operating the burner to it’s full potential (i.e. running it to it’s approved KW output)? An under-performing stove is an inefficient stove and will not be fully combusting the fuel, which again, results in tar creation.

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