External flue pipe extension

Yes you can get flue extension,and bends aswell.

So the flue vapor is what is im guessing causing discolouration, or making the wood deform. The flue vapor is acidic which comes from the inner flue. You can use a plume kit which is like a telescope on a submarine to divert the acidic fumes/vapor away to the open air, away from any openings or surfaces which are to close. Also check the manufacturer’s installation manual as they will specify the clearances and regulations regarding that particular applianc

Plume kit is required, however manufacturer instructions may say this is not a suitable method. All clearances must be adhered too or could cause some serious problems.

Check with manufacturer instructions it will tell you what is allowed.