Chimneys are a special kind of wall. Usually, walls wrap around us, but in this case, we wrap around chimneys. Probably that's why they are so appealing to us - they're almost like good friends, in the middle of our homes, protecting us from fumes and smoke, but giving us warmth through the cold time of the year.
Limit #2 Around the Chimney
But hold on: are chimneys really the good friends we can build upon? Obviously not: chimneys need a lot of maintenance to stay protective. Just another wall needing to be watched for, and one which might kill you and set your house on fire if you let your attention slip.