Your Fire Protection specialist
How old is your house? Actually, a better question is, How old is your chimney? Most people don’t put a lot of thought into their chimneys, but they should – especially if their home was built before the 1930s, when it became mandatory for U.S. chimneys to be built with liners. Chimneys in old homes typically don’t have chimney liners, and this can be a problem. Bricks and mortar are good at providing a route for smoke to leave the fireplace and at keeping gasses contained within the chimney on their way up. But bricks and mortar, like any substances, deteriorate over time. As time marches on and an older chimneys sees regular use, bricks will begin to crack. A number of forces are responsible for this including time itself, water damage, gasses that corrode and other factors. A sign that your chimney needs attention is smoke trickling out between the bricks. When bricks crack or crumble in close proximity to the inner wall surfaces of a home, a fire can easily start. The sheer heat can cause very dry wall material to combust, and creosote stuck to the chimney walls can ignite with just a few sparks. It’s smart to have yearly inspections, regardless of the age of your home, but for older homes it’s paramount.
Liners in chimneys serve three main functions:
1) The liner protects the house from heat transfer to combustibles. In the NBS tests, unlined chimneys allowed heat to move through the chimney so rapidly that the adjacent woodwork caught fire in only 3 1/2 hours.
2) Liners protect the masonry from the corrosive byproducts of combustion. In the tests it was determined that if the flue gases were allowed to penetrate to the brick and mortar, the result would be a reduction in the usable life of the chimney. The flue gases are acidic in nature and literally eat away at the mortar joints from inside the chimney. As the mortar joints erode, heat transfers more rapidly to the nearby combustibles and dangerous gases such as carbon monoxide can leak into the living areas of the home.
3) Liners provide a correctly sized flue for optimum efficiency of appliances. Modern wood stoves and gas or oil furnaces require a correctly sized flue to perform properly. The chimney is responsible for not only allowing the products of combustion a passage out of the house, but the draft generated by the chimney also supplies the combustion air to the appliance. An incorrectly sized liner can lead to excessive creosote buildup in wood-burning stoves, and the production of carbon monoxide with conventional fuels.