Most homeowners are aware of the need for chimney cleaning and inspection if they own a wood-burning stove or regularly use their fireplace, but many don’t realize that a gas heating appliance-whether it is a furnace, boiler or even a hot water heater-also relies on the chimney for proper venting of the exhaust. Appliances fueled by natural gas or propane may not produce the visible soot that appliances burning other fuels do, but they can deposit corrosive substances in your chimney. In many cases, these acids may wreak havoc on your chimney without producing any external symptoms until the problem has become dangerous or expensive to repair.
The problems lie with the modern higher efficiency appliances. These appliances gain their higher efficiency by extracting the heat that used to be sent up the chimney and delivering it to your home instead. No one wants to waste heat up the chimney, but a certain amount of heat is necessary in order to provide the draft that makes the venting system work, and to keep the chimney walls warm enough to prevent condensation of the flue gases. If the flue temperature becomes too low, as is often the case with modern appliances, two separate but interrelated problems- incomplete combustion and water condensation- can occur.
The situation is aggravated by cold exterior chimneys and long runs of connector pipe between the furnace and the chimney. Although your chimney may be suffering from an improper heating/venting match without producing any visible symptoms, sometimes the excess moisture produced causes visible results.
Eventually corrosion caused by this acidic water condensing inside the flue may cause the liner, mortar, and brickwork to flake and crumble. Chimney sweeps often find this debris creating blockages in the flue, potentially exposing the occupants of the home to carbon monoxide and other dangerous combustion byproducts, a situation not to be taken lightly.