I am doing same thing. there are lots of interesting sites such as
http://www.fluesystems.com/liners/in...mney_liner.htm and others if
you google for 'flue lining' etc. Much cheaper than local suppliers
and lots of diy advice. I'm going for stainless steel with loose
vermiculite backfill as this is easiest to fit and also serviceable -
easiest to replace if ever necessary.

cheers

jacob