Hot water is turning out to be a complicated issue. Everyone knows hot water is dangerous if it's too hot, but now there is a reason that it's a bad idea to keep it too cool.
For years, plumbing codes required hot water to be maintained at 140 degrees or more, and even hotter to promote sanitation for commercial and sterilization applications.
In the 1970s, the presumption that hotter was better lost favor because of the hazards presented by very hot water. Thousands of people were being severely burned every year by exposure to water so hot that it could scald in seconds. For that reason, since the 1980s new water heaters installed in houses have had the hot water temperature set at 125 degrees or less.
But many houses still have overly hot tap water, and tragedies still occur. Some homeowners turn up the temperature on newer hot water heaters to extend the hot water supply or to satisfy personal preference. Many older water heaters retain their original settings of 140 degrees or higher.
Hotter still, in many cases, is water from "summer-winter hookups" on hot-water boilers, in which domestic hot water for sinks and tubs is produced by the central heating system. Because boilers typically operate at 160 to 180 degrees when heating the house, the domestic hot water that comes out of them is often hotter than 150 degrees.
According to the federal Centers for Disease Control, most adults will suffer third-degree burns if exposed to 150-degree water for two seconds or 140-degree water for six seconds. By reducing the temperature to 130 degrees, the exposure time required for third-degree burns is extended to 30 seconds, and at 120 degrees, it takes five minutes.
Recommended burn-prevention measures are supervision of endangered children and adults, maintaining the hot water temperature at no higher than 125 and installation of thermal protection devices, which include whole-house thermostatic mixing or "tempering" valves on the hot water supply and anti-scald valves at the individual fixtures. Costs for these devices range from less than $100 to several hundred dollars, installed.
The issue of hot water temperature has been complicated recently by the finding that water heaters that are not hot enough can encourage the growth of the organism that causes potentially fatal Legionnaires' disease.
If Legionella bacteria are present in the water, Legionnaires' disease can be transmitted by any device that produces an aerosol, such as showers, faucets, humidifiers and whirlpool baths. Significantly, research has shown that Legionella can grow in water with a temperature between 68 and122.
Therefore, you've probably realized that there is a narrow temperature range - about 125 degrees - that is cool enough to avoid scalding and hot enough to discourage Legionella bacteria. If you invest in one or more thermal protection devices to protect against overly hot water, the water heater could be safely set a little higher than 125 degrees.
Most water heaters don't have a thermostat control that is calibrated in such a way that you can just dial in 125 degrees. So to check your hot water temperature, you'll probably need to use a reliable thermometer to check at a faucet.
Test the water temperature when the water heater is fully heated (e.g., not while it's reheating after you've taken a 20-minute shower). If you need to adjust the thermostat on it, allow half an hour after adjusting it before measuring the temperature again.
Dean Uhler has been a home inspector for more than 12 years and is president of Baltimore-based Boswell Building Surveys Inc. Uhler is a member of the American Society of Home Inspectors (ASHI) and is the treasurer of the Greater Baltimore Chapter of ASHI.
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