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Chimneys

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Definition

CHIMNEYS are passages or pipes that carry smoke and exhaust gases away through the walls or roofs of buildings.

Chimneys are essential to heating efficiency

1. Image of a Norman fireplace

1. This Norman fireplace vented through a wall,
a novel idea at the time.
Click the image for more information.


Over the decades of developing new furnaces and boilers, the chimney was usually ignored for its failings in ensuring efficient operation of the heating systems to which it was a major part. Of course, the designer and installer were largely blamed. But the unique characteristics of combustion and exhaust systems were not broadly understood for much of the past 150 years.

There were many studies of the chimney and manuals written to help over that time in Europe and North America. One professional comment, by C.R. Chadbourne, M.E., published in 1931 in Sanitary Age, a Canadian magazine, pointed to several areas of significance as areas for concern.

“To determine correctly the size and height of a chimney means almost as much work as making a complete set of heating plans. Because it is the very last thing to be determined upon, after the heating system has been designed for any specific building, under any specific conditions....

“The height of a chimney above the roof is one of the most important factors. It should extend well above all surrounding buildings that may interfere with its proper drafts.... The chimney largely determines the capacity of the boiler (or furnace).... Look to the chimney as the first place for trouble and carefully consider the chimney before installing a heating plant.... for no chimney that leaks will ever draw well.

“Fully 71 percent of all heating troubles with which a heating contractor has to contend is due to faulty chimney construction. Inspect the chimney and see that it is the size called for the boiler you are to install. If it is not, the heating system should not be installed until the chimney has been corrected,” Chadbourne stated.

Almost 60 years later, in a 1988 news report, Richard Hall confirmed this role of the chimney: “For many years, no one had been able to say definitively how furnaces and flues actually work. There were no standard formulas to describe something as seemingly common place as a basic house heating system. There were competing theories — and lots of folklore.

“That was because traditional math and modelling methods were just not capable of reducing the number and complexity of all the factors involved (in determining the correct chimney) to simple rules of thumb,” Hall wrote. It took computer software to begin that awareness by providing improved simulations for the dozens of factors that should be included in the final decision.

As a result of continuing back drafting and furnace flue gas spillage, Canada Mortgage & Housing Corp. (CMHC) had released Flueism software in 1983. Upgraded continuously with actual field studies, by 1988 CMHC supported this program with a series of chimney safety manuals. CMHC continues to provide technical assistance and ongoing practices to improve decision-making in many areas of home construction and renovation.

Section Gallery

2. Image showing a log cabin with a chimney in the centre3. Image of a modern woodstove chimney4. Image of a modern woodstove chimney pipe passing through a ceiling5. Image of a through-the-wall exhaust vent for a heater6. A page from a 1910 stove catalogue that stresses the importance of chimney height

Factually Speaking

The round chimney is the most efficient, followed by a larger square design.

A clever way to automate draft control

1. Image of an automated chimney draft control with self-balancing counterweight

The point at which the damper starts to open
automatically, reducing the draft over the fire,
is adjusted by moving the position of a counter
weight attached to a threaded rod on the
damper blade.
Click the image for more information.


The development of automated space heating equipment and systems, in the early years of the 20th century, was dependent above all on coming to understanding the principles of automation and regulation — making things work on demand without the touch of human hand.

The safe and efficient combustion of wood, coal, oil, and gas, in automated heating equipment with a conventional chimney, requires an automated draft regulating device. Some mechanism is needed to stabilize and limit the amount air being used for combustion. Conventional chimneys are subject to widely fluctuating draft conditions. Chimney draft is simply the amount of air that is being sucked up the chimney, as a result of natural forces.

The automated draft regulator is a simple, ingenious device that operates on a bypass principle. It limits the over-the-fire draft using the natural motive forces created by moving air currents and gravity. The unwelcome air is automatically bypassed and sucked up the chimney The draft regulator is mounted on the smoke pipe connecting the stove, furnace, or boiler to the chimney. An adjustable, delicately hinged damper blade, with adjustable counter weights, is set to open automatically in order to limit the volume of air passing over the fire, beyond what was required for safe, clean combustion.

This deluxe draft diverter by Draft-O-Stat, fabricated with cast-iron frame and black metal boot, is decorated in handsome red wrinkled finish. It represented the best engineering practice of the late pre–Second World War period. Like much automated heating equipment of the time, it was solidly built and beautifully finished to appeal to the high-end market of the period — the only market that existed in a period of economic depression and hard times.

Yet devices of this nature would soon become familiar fixtures in Canadian homes. They would be heard opening and closing, often with a familiar, friendly, and reassuring bump — signaling that the heat was on, and all was right with the automated home heating system, out of sight and largely out of mind.

Section Gallery

2. Detail of chimney damper starting to open, automatically3. Image showing the adjustment mechanism for setting the damper to open and close automatically4. Image showing a springless damper design from 1886


Article Sources

Chimneys are important to heating efficiency

  • Research from the archives of the HVACR Heritage Centre Canada (DCSB #104).
  • C.R. Chadbourne, M.E., "Relation of Chimneys to Efficient Heating." Sanitary Age, August 14, 1931.
  • Richard Hall, "Chimney Computer Simulation." Heating-Plumbing-Air Conditioning, September 1988.
  • “Chimney Safety Tests Manuals.” Heating-Plumbing-Air Conditioning, September 1988. “Canada Mortgage and Housing | Société canadienne dhypothèques et de logement.” Canada Mortgage and Housing | Société canadienne dhypothèques et de logement. http://www.cmhc-schl.gc.ca (accessed August 26, 2010).
  • Air conditioning and refrigeration: a complete training program, Series C: Heating--Part1 (Chicago: Refrigeration and Air Conditioning Institute, Inc., 1938), 6-2 to 16-5.
  • A standard ordinance for chimney construction, suitable for use in cities and towns of any size or as a state law, 3d ed. (New York: National Board of Fire Underwriters, 1927).
  • American Society of Heating, Refrigerating and Air-conditioning Engineers, ASHRAE Guide and Data Book, Fundamentals and Equipment (New York, NY: n.p., 1961), 677-90.
  • KeepRite Products Ltd., Construction Products Div., Fire-chief Thermo-Lok Product Bulletin (Brantford, ON: n.p.,1961).
  • Ibid., Total Chimney-System Sizing Guide, for Class A factory-built chimneys, (Brantford, ON: n.p.,1960), 20 pages.

A clever way to automate draft control

  • Research from the archives of the HVACR Heritage Centre Canada (DSCB #3, HD1001I).
  • Historical artifact from the HVACR Centre Canada T.H Collection Accession No. 2006-116.

SIDEBAR: More About Chimneys

  • Research from the archives of the HVACR Heritage Centre Canada (DSCB #3; DCSB #104).
  • Air conditioning and refrigeration: a complete training program, Series C: Heating--Part 1 (Chicago: Refrigeration and Air Conditioning Institute, Inc., 1938), 6-2 to 16-5.
  • American Society of Heating, Refrigerating and Air-conditioning Engineers, ASHRAE Guide and Data Book, Fundamentals and Equipment (New York, NY: n.p., 1961), 677-90.
  • KeepRite Products Ltd., Construction Products Div., Fire-chief Thermo-Lok Product Bulletin (Brantford, ON: n.p.,1961).
  • Ibid., Total Chimney-System Sizing Guide, for Class A factory-built chimneys, (Brantford, ON: n.p.,1960), 20 pages.
  • A standard ordinance for chimney construction, suitable for use in cities and towns of any size or as a state law, 3d ed. (New York: National Board of Fire Underwriters, 1927).

Factually Speaking

  • Did you know that ... http://www.centreforenergy.com/AboutEnergy/Electricity/Generation/History.asp.

Image Credits

Chimneys are important to heating efficiency

  • Dick and Jane Travel (Own work) [CC-BY-2.5 (www.creativecommons.org/licenses/by/2.5)], via www.fmschmitt.com/travels/England/london/toweroflondon/firstfloor.html.
  • William Notman, I-64940, Notman photographic Archives - McCord Museum.
  • Nigel Heseltine, HHCC.
  • Ibid.
  • Ibid.
  • The D. Moore Company, Limited, Illustrated Catalogue and Price List No. 61, Treasure STOVES and Ranges, 1909–10 (Hamilton, Ontario, n.p., 1909).

A clever way to automate draft control

  • Mark Dorlandt Photography, HD1006A-27-117.
  • Ibid., 27-119.
  • Ibid., 27-122.
  • Combined Catalogue and Wholesale Price List of "Perfection" Stoves, Ranges and Furnaces, "Favorite" Stoves and Ranges. The James Smart Mfg., Co., Limited, Brockville, Ontario, Canada. p109.