Cowl (chimney)

Cowl (chimney)
Cowl designs from a 1910 catalogue

A cowl is a usually hood-shaped covering used to increase the draft of a chimney and prevent backflow. The cowl, usually made of galvanized iron, is fitted to the chimney pot to prevent wind blowing the smoke back down into the room beneath. No doubt named for the resemblance of many designs to the cowl garment worn by monks, they have been in use for centuries.

When using an open fire to heat a room the smoke rises through a flue to a chimney pot on the roof. Under normal conditions the warm air from the fire will rise up the chimney taking the smoke with it and dispersing it at rooftop level where it is less of a nuisance.

In strong winds the force of the wind may overwhelm the updraft and push the airflow in reverse down the flue. Smoke will then fill the room it is intended to heat posing a health and fire risk, causing discomfort and dirtying furnishings.

When raw coal rather than smokeless fuel is burnt, which was the case for centuries before clean air legislation took effect, then the amount of smoke is considerable and measures to prevent backflow occurring are a necessity.

Another secondary function is to prevent birds and squirrels from nesting in the chimney. They often also act as a rain guard to keep rain from going down the chimney. A metal wire mesh is sometimes added as a spark arrestor. Wooden cowls were used on oasts to prevent the ingress of rain into kilns, and create a flow of air through the kiln.

A H-style cap (cowl) is a chimney top constructed from chimney pipes shaped like the letter H. It is an age-old method to regulate draft in situations where prevailing winds or turbulence cause downdraft and backpuffing. Although the H-cap has a distinctive advantage over most other downdraft caps, it fell out of favor because of its bulky looks. It is found mainly in marine use but has been gaining popularity again for its energy saving functionality. The H-cap stabilizes the draft rather than increases it. Other downdraft caps are based on the Venturi effect, solving downdraft problems by increasing the updraft constantly resulting in much higher fuel consumption.

Examples

References


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  • Cowl (disambiguation) — A cowl may refer to: Cowl, a garment worn by monks Cowl (chimney), a device fitted to a chimney pot to prevent wind blowing the smoke back down into the room beneath Cowl (oast), the revolving device found on oasts, maltings, and breweries Cowl… …   Wikipedia

  • Cowl — (koul), n. [AS. cuhle, cugle, cugele; cf. dial. G. kogel, gugel, OF. coule, goule; all fr. LL. cuculla, cucullus, fr. L. cucullus cap, hood; perh. akin to celare to conceal, cella cell. Cf. {Cucullate}.] 1. A monk s hood; usually attached to the… …   The Collaborative International Dictionary of English

  • cowl — cowl1 [koul] n. [ME coule < OE cugle < LL(Ec) cuculla < L cucullus, cap, hood < ? IE base * (s)keu , to cover > SKY] 1. a) a monk s hood b) a monk s cloak with a hood 2. something shaped like a cowl; esp., a …   English World dictionary

  • cowl — [kaul] n [: Old English; Origin: cugele, from Latin cucullus] 1.) a large ↑hood that covers your head and shoulders ▪ a monk in a dark habit and cowl 2.) a cover for a ↑chimney …   Dictionary of contemporary English

  • cowl — [ kaul ] noun count 1. ) a part of a piece of clothing that covers the head and shoulders, worn especially by MONKS 2. ) a cover for a CHIMNEY that improves the flow of smoke …   Usage of the words and phrases in modern English

  • cowl — ► NOUN 1) a large loose hood forming part of a monk s habit. 2) a hood shaped covering for a chimney or ventilation shaft. 3) another term for COWLING(Cf. ↑cowling). DERIVATIVES cowled adjective. ORIGIN Latin …   English terms dictionary

  • Chimney — For other uses, see Chimney (disambiguation). Smokestack redirects here. For the 1963 avant garde jazz album, see Smokestack (album). The world s tallest chimney, of GRES 2 in Ekibastuz, Kazakhstan. A chimney is a structure for venting hot flue… …   Wikipedia

  • cowl — /kaʊl / (say kowl) noun 1. a hooded garment worn by monks. 2. the hood of this garment. 3. a hood shaped covering for a chimney or ventilating shaft, to increase the draught. 4. the forward part of the motor vehicle body supporting the rear of… …   Australian-English dictionary

  • cowl — /kowl/, n. 1. a hooded garment worn by monks. 2. the hood of this garment. 3. part of a garment that is draped to resemble a cowl or hood. 4. the forward part of the body of a motor vehicle supporting the rear of the hood and the windshield and… …   Universalium

  • chimney pot — noun A short earthenware pipe, placed on top of a chimney to improve the draft. A chimney cowl / terminal can be fixed over a chimney, if required …   Wiktionary

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