Why You Should Insulate Your Chimney Flue!

Why insulate a flue? Is it worth insulating your masonry chimney?

There is no doubt that an insulated flue liner makes your masonry chimney perform and draught better than an uninsulated one – but why insulate your chimney flue? 

The main reason to insulate your chimney liner is to ensure that it warms up faster than a liner without insulation (less heat loss from the exposed metal liner inside the masonry chimney).

When a flue liner is warmer, the flue gases inside the flue remain warmer for longer and rise more rapidly – this upwards movement aids the burning of the fuel inside your stove which means more heat in the room for you!

In addition, a hot burning stove aided by a correctly draughting chimney will mean;

  1. Less sooty or creosote deposits collecting on the inside walls of the flue – these can potentially ignite and cause a chimney fire.
  2. Less particulate emissions being released into the atmosphere which can be hazardous to human health.
  3. The stove or fireplace will be less susceptible to wind that can force the fumes and gases down the chimney, causing a downdraught.
  4. The chimney will be less likely to suffer from cold air sinking down through it after the stove or fireplace has gone out.
  5. The chimney is unlikely to suffer from a lack of draught where the fumes cannot escape upwards during combustion.

When is it necessary to insulate a chimney?

If the chimney shaft is very wide, for example, 45cm x 45cm or more, there will be a large cold air void around the flue contained in the masonry chimney. This cold space will take heat from the flue liner if not insulated and may cause the chimney to draught incorrectly.

If the chimney breast is proud of the wall and surrounded by cold air on three sides it is important to insulate the flue

If the flue is contained in a long free standing chimney stack surrounded by cold air on four sides.

If your chimney is short. Shorter chimneys do not draught as well as longer chimneys, therefore, it is advisable to help improve the draught in a short chimney by insulating it.

What can be used to insulate a flue?

An insulating blanket or wrap such as SHL's AGC Thermal Wrap which is slipped over the flexible flue liner as it is being installed.

A granular mix of vermiculite or perlite granules which are poured around the flue liner – beware of old chimneys which may have holes or have become porous – the granules may flow out into another flue or section / room of the dwelling.

It is recommended to always fit a chimney cowl after you have installed and insulated your flexible liner. Certain chimney cowls are known to aid draught, please read about our range of chimney cowls here.

If you would like to read about the types of flexible liner we stock, including stainless steel grade and diameters, please click here.

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