How long a run of single skin flue pipe can I use?

We recommend that up to 1000mm of single skin flue pipe can be used, with an absolute upper limit of 1500mm. The reason for this is that single skin flue pipe is uninsulated and so will have the effect of warming the room but also of cooling the flue gases. When flue gases cool chimney desposits increase and the risk of chimney fire. You might like to read more about chimney fires