Regret the Error

The Nov. 12 article “Public Bathroom Dilemma: Paper or Air?” misstated how much energy is consumed by hand dryers. The corrected story now says that “5.7 million kilowatt-hours of electricity [are] used every day — enough power to run an estimated 197,000 homes a day.” The following explains how author Rebecca Clarren reached the new calculation. Watts are an expression of energy per unit of time, namely 1 joule per second. A kilowatt-hour (kWh) is not a standard unit in any formal system, but is commonly used in electrical applications as a measure of energy use and is used by power companies. Since 1 kWh = 3,600,000 joules, to get the correct calculation (now reflected in the original story), Clarren multiplied the average hand dryer’s wattage, 2.3 kWh, by 0.0083 (how long a second is expressed in hours), and came up with 0.019 kWh. Then she multiplied that by the 3 million hand dryers that exist nationwide, X 100 uses per day, and came up with a total of 5.7 million kWh used by hand dryers every day. Based on the latest figures from the Energy Information Administration, the average household uses 10,654 kWh a year, or 29.19 kWh a day. Therefore, 5.7 million kWh divided by 29.19 kWh a day in home(s) equals approximately 197,000 homes a day. Also, the story now contains an updated link to the comparison of paper towels and hand dryers that the Climate Conservancy did for Salon. Link