Many people that use a gas heating appliance (furnace, boiler, gas-water heater, etc.) do not realize that it still relies on the chimney to be properly vented. These type of gas appliances may not produce visible soot like a regularly burning fireplace or a wood-burning stove, but they do deposit corrosive material inside a chimney. These materials can eventually lead to severe chimney damage that will not result in external symptoms until the problem has become dangerous and expensive to repair.
The problem with these gas fireplace appliances is that they have been made to have higher efficiency to prevent heat from escaping through the chimney. However, for the flue temperature to remain at the proper temperature some heat needs to be released. When this heat is not released with modern gas appliances, condensation of flue gases begin to build up, and this causes two separate but interrelated problems- incomplete combustion and water condensation.
When a chimney is too cool to create an adequate draft, this means that not enough combustion air is being pulled into the chimney. When burning one foot of natural gas, ten cubic feet of air is needed to get an adequate amount of oxygen for combustion. If this does not happen inside a chimney, the gas appliance can produce carbon monoxide and heat efficiency will suffer anyway.
For those unaware natural gas and propane are hydrocarbons. The combustion of hydrocarbons results mostly in carbon dioxide and water vapor. The average furnace will put out 1 1/2 gallons of water into the chimney per hour. Since newer high efficiency gas furnaces steal the extra heat that the chimney uses to keep this moisture from condensing, the water will often condense inside the cooler flue.
This becomes even more problematic because the water condensation that builds up is often highly acidic and corrosive. This is from normal air pollution, cleaning supplies, and depending on what the chimney was previously used for- example coal or oil. Now, not only is water building up inside the chimney, but it is also a dilute hydrochloric or sulfuric acid that will eat away at the chimney’s brick and mortar from the inside. A further condensation problem is caused by a cold exterior chimney and long runs of connector pipe between the furnace and the chimney. Sometimes the excess moisture will lead to visible results including:
-Damp patches on interior walls or exterior walls
-Stain on the ceiling around the chimney
-White stains (efflorescence) on the outside of the masonry chimney
-Eroded mortar joints
Eventually, if something is not done, corrosion from the acidic water may cause liner, mortar, and brickwork to flake and crumble. A chimney sweep will typically find debris from the corrosion that blocks the flue. This is an extremely dangerous point to reach as it exposes the family to carbon monoxide and other dangerous byproducts.
A solution for all gas fireplace owners is to have a certified chimney sweep perform regular inspections of the chimney and venting system. If they do discover any problems, they will be able to install a correctly sized, insulated liner and rework the connection between the chimney and the furnace. This is to resize the flue to allow better draft and minimize condensation.
Read for More Information:
Factory-Built Fireplaces vs Masonry Fireplaces
Four Common Problems That Require a Chimney Sweep
Wells & Sons Chimney Service offers chimney cleaning, repair and maintenance, gas and pellet stove installations, whole home masonry and stucco, and dryer vent cleaning. We have been providing superior chimney services to the Pottstown, Allentown, Reading, Norristown, West Chester, Lansdale, and surrounding Pennsylvania areas since 1979.