On Tue, 10 Apr 2018 17:09:33 +0200, Martin wrote:

On Tue, 10 Apr 2018 15:03:12 +0100, Peter Parry wrote:

Depends on how much you like oily brown condensate dripping into the
food you are cooking.

Grease and oil will coat the inner surface after some time and while
some will drip back the rest will remain and in the event of a pan
fire on the hob will turn a difficult problem into a really serious
one. To minimise the risk of fire spreading up the flue you should
fit a fire flap/damper. Using a filter on the fan will not
significantly alter the amount of oil/fat going up the chimney and
most will condense on the chimney liner.

That depends on whether the extractor hood has a replaceable filter and how
often you change it. It works for us.

From what you have said yours is horizontal pipe before joining an
existing chimney. The proposed solution is a long vertical metal pipe
so the temperature drop and condensation of oils and fats will be far
worse. The mesh grease filters will stop some oil and grease but by
no means all. In a long vertical pipe what remains will condense out
and eventually trickle back down.