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 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. 

Chimney wrap

Installing with a chimney wrap: Instead of feeding the flue 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

Vermiculite (Micafil) 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.