What problems can condensation cause?
All natural draft chimney function due to temperature differences between the outside of the home and the exhaust gases. The draft created by this temperature difference draws the exhaust gases produced by a fireplace or appliance safely out of the chimney.
Most all fuels have as a by product of combustion elements which can condense when they come into contact with cooler surfaces. In the case or wood fired appliances and fireplaces, creosote is the condensing by-product. As shown in the picture to the right, creosote condensation can be substantial when conditions are right for condensation to occur. Creosote is the fuel for chimney fires. The best way to ensure a chimney fire will not occur is to not have the fuel for it in the first place. In the case of natural gas or propane fired appliances the primary condensate is water. This condensation can speed up water damage to a chimney via the freeze / thaw cycle. Permanent damage to a chimney can be cause cracks in the structure of the chimney leading to structural failure or exhaust gases seeping into living space.
The key to a condensation problem relates both to proper sizing of a vent system and its proper design and construction. This condition is a cool or cold flue. A cold flue which does not heat up properly is a surface ready to hold condensation.