Q: We went to considerable expense to remodel and upgrade our primary bathroom, only to learn upon completion that the shower is not hot enough. The contractor told us that the manufacturers now have guards on the hot water handle to prevent children from being scalded. It’s a primary bath, presumably used for adults, and there are no small children in our home. The contractor didn’t tell us about this “new” regulation before starting the project. How can these manufacturers unilaterally decide that no one can have a hot shower?
A: First, the change isn’t really “new.” And second, there may be a way to adjust the water temperature via your hot water heater or within the shower valve so that you can take a shower that’s satisfyingly hot but not dangerously so.
A history of attempts to regulate maximum hot water temperatures, published in the online magazine Plumbing & Mechanical Engineer, explains how we got to the situation you face. For decades, plumbing codes dictated that hot water in homes was required to be at least 120 degrees — a minimum, not a maximum. Plumbers often set the thermostat much higher, which was an easy way to prevent callbacks when customers found their hot water running out when multiple people showered in a short time. If water from the water heater was hotter, people could add more cold water when they showered, stretching out the hot water supply. The showers had simple mixing valves that allowed people to adjust how much water was coming from the hot and cold pipes.
Then came the oil embargo of 1973. Heating hot water to a lower temperature was an easy way to conserve energy. Maximum settings of 140 degrees became common, although hot water was still supposed to be at least 120 degrees. Since then, the recommended maximum settings for hot water tanks have varied, to as low as 110 degrees. Water at 140 degrees can cause serious burns within 3 seconds, but if the water is 120 degrees, it takes about 10 minutes — enough time for someone to step away unless the temperature gets hot so fast that they panic and slip. Setting a water heater to 120 degrees also guards against growth of the bacteria that cause Legionnaire’s disease; 110 degrees isn’t enough for that.
To conserve both water and energy, plumbing codes began requiring shower heads that limit flow to 3 gallons per minute, instead of the 5 to 10 gpm common in older shower heads. Suddenly, a lot more people were getting scalded in showers. Researchers found that low-flow shower heads were the reason, because a sudden change in water pressure — maybe because someone flushed a nearby toilet while someone else was showering — has a much bigger effect on water temperature when the flow is low. In 1990, plumbing codes began requiring protection against that, and the industry shifted mostly to shower valves that keep the temperature relatively constant even if pressure changes. Now, the 2021 International Residential Code, which is in effect in much of the United States, requires that valves for showers or tub-shower combinations have a maximum setting of 120 degrees — and it says the valves need to be adjusted after they are installed to make sure the water isn’t hotter.
Pressure-balancing valves, also known as anti-scalding valves, are designed to keep water temperature from changing more than a few degrees if the pressure changes. You probably have this type of valve; it’s the most common today. The valves usually have a single handle, which controls the ratio of water coming from the hot and cold pipes. The valve does not keep the flow constant. If the pressure in the cold-water line drops, the amount of water coming from the hot-water line also drops. A low-flow shower can feel cold, even if the temperature doesn’t change. More significantly, a pressure-balancing valve does not regulate temperature directly, just the ratio of hot to cold water. In the winter, when water coming into a house is a lot colder than it is in the summer, a setting that gives you 80 percent hot water and 20 percent cold water is likely to make the shower much colder than it is with the same ratio in the summer.
And if your water heater is at one end of the house and your shower is at the other, the hot water going into the showerhead is probably a lot colder than it was when it left the water heater.
Before you give up on being able to enjoy a comfortable shower, test what is happening in your house. Turn the shower handle so as much hot water as possible is coming out. Let the water run until the hot water pipe is clear of any water that cooled in the pipes since the last shower, then measure the temperature. If it’s far below 120 degrees, one possible solution is to adjust your hot water heater’s thermostat. Wait two hours, then recheck the shower temperature. Also measure the water temperature at other faucets or showers to make sure no flows exceed 120 degrees.
If the new setting causes temperatures that are too high elsewhere but not at the shower, you may be able to adjust the shower’s pressure-balancing valve so it draws more water from the hot tap and less from the cold tap when the handle is all the way on (to the left). Moen, a faucet and valve manufacturer, notes in the installation instructions for its Posi-Temp Tub and Shower Valves that the temperature limit device within the valve might need to be adjusted seasonally because of the way the temperature of incoming cold water varies. Yet, given how frequently the setting might need to change, there is no obvious way to do the adjustment.
You need to partially disassemble the faucet and change alignment on a part called the “temperature limit stop.” Check the installation instructions for the shower control you have, or do a Web search for something like “how to adjust the temperature on a XX shower valve,” with the XX being the brand you have. If you can’t figure it out, ask a plumber. But be aware that even if you love hot showers, you probably don’t want to shower at 120 degrees. A good maximum might be 110. Skin-care experts often recommend much lower.
Another option, which would have been better to know about before you remodeled, is to invest in a thermostatic valve, which is designed to maintain both pressure and temperature. But these valves are more expensive. At Home Depot, a Moen pressure-balancing valve with a chrome handle and trim is $172.07. But if you want a thermostatic valve, a basic Kohler model is $384.79 and you need to purchase a handle and trim kit separately. A Delta two-handle chrome trim kit is $239.09. Valves and handle trim kits go up in price depending on the features. Variations may have multiple handles to allow water to flow through more than one showerhead or from body jets. But the biggest issue for you at this point probably isn’t the cost. To install a different valve, a plumber would need to cut into the wall — not something people who have just remodeled are likely to want.
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