Naturally drafting residential chimneys develop draft because the air inside the chimney is lighter than the air outside the chimney.
The source of the heated air at the bottom of the chimney burns fuel and creates a column of gases that are lighter than the outside air. The taller the chimney and the hotter the contents – the greater the draft.
Today, with the installation of more efficient heating systems that vent their combustion gases through fan-assisted plastic vents, it is often left up to the fuel burning water heater to create enough heat by itself to make a sufficient draft to vent the combustion gases through a chimney that was originally designed for much more heat provided from both appliances.
The water heater’s over sized chimney now needs a chimney liner.
The need for chimney liners is often ignored when the heating system has been upgraded and the potential for dangerous combustion gases to enter the living space is increased. Unlined chimneys and those deteriorated from acidic combustion gases should be upgraded, as well, to include stainless steel, aluminum or masonry liners.
For more information about inspections of mechanical systems for safety and efficiency, visit http://www.missouricertifiedenergy.com.