Ice On My Chimney

January 18, 2017


Photographer: Dale Hugo
Summary Author: Dale Hugo

The cold weather snap here in the Midwest U.S. in December 2016, had consequences for my chimney in terms of ice buildup. No, our recent big snows (17 in or 42 cm during a 10 day period) didn't melt down from the top of the chimney, rather water vapor condensing on the cold metal once it's vented from the furnace caused the icing. Why would my furnace vent water vapor? Two reasons: 1) I have a humidifier running, and since my furnace burns indoor air, that moisture must go somewhere; 2) Methane gas is also being burned. Burning any hydrocarbon produces carbon dioxide and water vapor.

Carbon dioxide has a boiling point far below that of water's freezing point (32 F or 0 C) -- too low to condense on the Earth's surface. But of course, water vapor will condense and freeze on cold surfaces, typically at temperatures of about 14 F or -10 C. The temperature dropped to -7 F (-20 C) at my home in northeastern Illinois, during last month's cold snap. Thus, the icicles. Since most automobiles and trucks burn hydrocarbons, you'll notice, when it's cold, vapor swirling out from the tail pipe. This water vapor usually evaporates into the air a few feet behind the vehicle. However, you never see the carbon dioxide.

Notice that the icicles are all on one side of the chimney, the southeast side. Why? Prevailing winds at this latitude are from the northwest during winter, so the ice forms on the side opposite of the predominant wind direction. Photo taken on December 19, 2016.

Photo Details: Camera Maker: Apple; Camera Model: iPad 2; Focal Length: 2.0mm (35mm equivalent: 105mm); Digital Zoom: 2.384x; Aperture: ƒ/2.4; Exposure Time: 0.0005 s (1/1912);
ISO equiv: 40.