Question: A chimney sweeper recently told me I have a hole in the mortar between my flue tiles. He says it is about 1.5 inches in diameter and is 6 ft from the top of my 40 foot tall chimney. My entire chimney knowledge comes from 30 min with him, so forgive the ignorant and obvious portions. The flue is made of some kind of super clay, and there are two of them encased in one brick chimney because there are two fireplaces. There is a screen on top of the chimney which has collected straw. We have had problems lately with smoke coming into the house. The chimney sweeper says the hole somehow creates a risk of carbon monoxide getting into the house and recommends a flue insert made of metal which is extra expensive since this flue bends to meet the other flue and come out of the chimney. Since the space between the flue and the chimney is sealed at the top and bottom, I have a hard time comprehending a draft through that hole. What do you recommend? Answer: If the chimney is working well, and no smoke has been leaking into the home, then lining may be overkill. It is very rare for such a chimney to leak CO into a house, and you'd smell wood smoke long before there was any real danger. If the hole is that small, and that close to the top, why not just patch it with some high-temp cement. I'm sure the sweep could figure out a way to get a patch into that hole. One way to to make a squeegee out of rubber a little bigger than the size of the chimney and fix a pole to the center of it. Push it down the flue past the joint..pour in some cement, and then drag it upward. It will then force cement into the crack.