The long-term effects on clay tile flue liners venting oil-fired appliances can be gradual deterioration of the liner due to the acidic nature of the chimney residue. This process can occur over many years. The liner walls can soften and flake off material opening holes through the liner walls. If this happens, the flue must be relined.
New high efficiency oil-fired appliances require smaller flue sizes than older units. Where an old unit may require an eight-inch flue, the replacement unit’s installation instructions may call for a five-inch flue.
This is a 60% reduction in flue size. Couple that with lower flue gas temperatures of new units and the flue size becomes much more critical to the proper operation of the present day oil-fired appliance.
In cold, oversized masonry chimneys, the less-hot flue gases of modern appliances quickly expand and cool even more. Draft is drastically reduced because it depends upon the buoyancy of the hot flue gases. The cooler the gases become, the slower they move up the flue and the more the draft is reduced. This will reduce an appliance’s efficiency and increase fuel consumption. The longer the flue gasses remain in the flue, the greater the risk of leakage into the home.
Water vapor, a normal by-product of combustion, condenses on the cool internal surfaces of oversized flues. This problem is worse in exterior chimneys and cold climates. The resulting moisture can be absorbed by the chimney and transferred through the walls. It may cause paint to peel, and wallpaper and plaster to fall. In winter, wet chimneys experience numerous freeze/thaw cycles causing bricks and clay tile liners to spall or flake, mortar joints to erode, and water leakage at the bottom of the chimney.
Dangerous carbon monoxide gas can be forced into your home through open mortar joints, cracked flue liners and flues blocked by debris. Deterioration of the flue liner can occur when venting oil fired appliances. Chemical compounds such as sulfur residues from the oil and chlorides from the laundry area, when combined with water, form highly aggressive acids capable of causing considerable damage to flue tiles in masonry chimneys.
Retrofitting a chimney with a UL Listed, properly sized and properly installed chimney lining system is the most important and easiest way to prevent these problems.
A properly sized chimney lining system will insure correct draft by preventing the flue gases from expanding and cooling more than they should. Properly-sizing a chimney liner will greatly reduce condensation within the venting system. The hot and buoyant flue gases will remain hot, exit the flue quicker, cool less and be much less likely to condense on the chimney or liner walls. By using a watertight flue liner any condensation that might form is contained within the liner, thereby avoiding further damage to the chimney from freeze/thaw cycles and corrosion from the highly acidic condensate.
A UL Listed, stainless steel flue liner or a UL Listed, cast-in-place chimney lining system designed to vent the flue gases of oil-fired appliances should be installed.
A Certified Chimney Sweep can properly evaluate, size, recommend and install the appropriate chimney liner for your home heating equipment.