Vermiculite is a light weight naturally occurring mineral which is an excellent heat insulator.
It can be used to pour back down the chimney filling the void between the brick chinmey and the flexible flue liner.
This will improve the performance of your stove by ensuring the flue gases stay warm enough to escape quickly therefore ensuring the draw of the chimney stays strong.
It also massively reduces condesation of the flue gases ensuring your flue liner has a much longer life.
Each bag is light weight and full of small particles which can easily be poured back down the chimney.
Backfilling your liner is not essential but it definitely helps. Also, as the Vermiculite aids performance and efficiency of your stove, you will be using less fuel.
HOW MUCH WILL I NEED?
Every chimney will be different,please refer to your HETAS registered installer.