Older homes have been built with masonry chimneys which were designed for low efficiency heating systems. When replacing your old furnace with a high efficiency one your chimney may require modification to assure that it is sized to fit your new heating system. It may not remove combustion gases properly, possibly leading to back drafting and allowing combustion gases such as carbon monoxide to enter your home. That is why it is very important to properly size and install chimney liners. So please give us a call if you are concerned about your chimney condition as we also do chimney liner inspections.