Insulating a flexible liner
Insulated flues improve the draw.
Do we need to insulate when we fit a chimney liner?
- If the chimney is exposed (on an outside wall), or
- the stack is particularly tall, or
- the flue is of a large diameter
then the answer to the proposed question above is a definite YES! Insulated liners keep the flue gases warmer, increase the upward speed of those gases and help prevent condensation.
Otherwise it is not necessary. The air between the liner and the flue will insulate the liner.
However, it is not difficult to insulate a liner (just adds cost) so it is up to you.
Fitting is straightforward. Instead of feeding it down the chimney you haul it up the chimney. The person at the top has to have a very secure platform (e.g. scaffolding). A cherry picker might work but add the liner and wrap weight to the maximum allowed by the cherry picker.
Vermiculite (Micafil, pictured, is a brand name) is supplied in bags. It is very light and will be taken by the wind easily.
Vermiculite cannot catch fire and is used to insulate around chimney liners. It is poured into the top of the chimney and will cascade down the chimney onto the closure plate, filling the gap between the liner and the chimney itself all the way to the top.
Vermiculite is only suitable for chimneys with a few inches of air gap. If your liner has more than a few inches of air gap you are going to use a heck of a lot of Vermiculite. To be safe allow 1 bag for each metre of chimney you need to fill.
The simplest method of filling is to obtain one of those “Gorilla buckets” as favoured by builder’s or horsey folks. Cut a hole in the bottom just slightly smaller than the hole at the top of your pot then slip it over the bit of liner sticking out of your chimney pot. Tape it to the pot using Gaffer tape or similar. Pour Vermiculite into your new “funnel” (the bucket”) and keep doing so until your chimney is full.
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