How can I make the water in my shower hotter?

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Q: We spent a significant amount of money remodeling and updating our master bathroom, only to discover upon completion that the shower wasn't hot enough. The contractor told us that manufacturers now have guards on the hot water handle to prevent children from scalding themselves. It is a primary bathroom, presumably used for adults, and there are no small children in our home. The contractor did not inform us of this “new” regulation before the project began. How can these manufacturers unilaterally decide that no one can take hot showers?

A: First, the change is not really “new.” And second, there may be a way to adjust the water temperature via your water heater or in the shower valve so that you can take a comfortably hot but not dangerous shower.

A story of attempts to regulate the maximum hot water temperature published in the online magazine Plumbing & Mechanical Engineer explains how we got to the situation you are facing. For decades, plumbing codes required household hot water 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 because multiple people were showering in a short period of time. If the water from the water heater were warmer, people could add more cold water when showering, extending the hot water supply. The showers had simple mixing valves that allowed you to adjust how much water came 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 save energy. Maximum settings of 140 degrees became common, although hot water should still be at least 120 degrees. Since then, the recommended maximum settings for hot water tanks have changed, reaching as high as 110 degrees. Water that is 140 degrees can cause severe burns within 3 seconds, but if the water is 120 degrees it will take about 10 minutes – enough time for someone to step back unless the temperature rises so quickly that they panics and slips. Setting a water heater to 120 degrees also protects against the growth of the bacteria that cause Legionnaires' disease. 110 degrees is not enough for that.

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To save both water and energy, plumbing codes for the first time required showerheads that limited flow to 3 gallons per minute, instead of the 5 to 10 gallons per minute typical of older showerheads. Suddenly, many more people were suffering from scalding injuries while showering. Researchers found that low-flow showerheads were the reason for this, as a sudden change in water pressure – perhaps because someone was using a nearby toilet while someone else was showering – has a much greater impact on the water temperature when the flow is low . In 1990, plumbing codes required protection against this, and the industry shifted primarily to shower valves that maintain the temperature relatively constant even with pressure changes. The 2021 International Residential Code, in effect across much of the United States, now requires valves for showers or tub-shower combinations to have a maximum setting of 120 degrees – and states that the valves must be adjusted after installation to ensure that the water doesn't get hotter.

Pressure equalization valves, also called anti-scald valves, are designed to prevent the water temperature from changing by more than a few degrees when pressure changes. You probably have this type of valve; it is the most common today. The valves usually have a single handle that controls the ratio of water from the hot and cold pipes. The valve does not keep the flow constant. If the pressure in the cold water pipe decreases, the amount of water coming from the hot water pipe also decreases. A low-flow shower can feel cold even if the temperature doesn't change. More importantly, a pressure equalization valve does not regulate temperature directly, only the ratio of hot to cold water. In the winter, when the water flowing into a home is much colder than in the summer, a setting that provides 80 percent hot water and 20 percent cold water will likely make the shower much colder than 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 end, the hot water flowing into the showerhead is likely much colder than when it left the water heater.

Before you give up a comfortable shower, test what is happening in your home. Turn the shower handle so that as much hot water as possible comes out. Let the water run until there is no more water from the hot water pipe, which has cooled in the pipes since the last shower, and then take the temperature. If the temperature is well below 120 degrees, a possible solution is to adjust your water heater thermostat. Wait two hours and then check the shower temperature again. Also measure the water temperature on other faucets or showers to ensure the water temperature does not rise above 120 degrees.

If the new setting is causing excessive temperatures elsewhere but not the shower, you may be able to adjust the shower's pressure balancing valve to draw more water from the hot faucet and less from the cold faucet when the handle is fully open further (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 limiting device in the valve may need to be adjusted seasonally because the temperature of the incoming cold water fluctuates. However, given the frequency with which the setting needs to be changed, there is no obvious way to make the adjustment.

You will need to partially disassemble the faucet and change the orientation on a part called the “temperature limit stop.” Look at the installation instructions for the shower control you have, or search online for something like “How to adjust the temperature on an XX shower valve,” where XX is the brand you have. If you can't figure it out, ask a plumber. But be aware: Even if you love hot showers, you probably don't want to shower in 120 degrees. A good maximum might be 110. Skin care experts often recommend a much lower value.

Another option you should know more about before remodeling is investing in a thermostatic valve designed to maintain both pressure and temperature. However, these valves are more expensive. At Home Depot, a Moen pressure balancing valve with chrome handle and trim costs $172.07. However, if you want a thermostatic valve, a base Kohler model costs $384.79 and you'll need to purchase a handle and trim kit separately. A Delta two-handle chrome trim kit is $239.09. Depending on the equipment, the prices for valves and handle trim sets increase. Variations may have multiple handles to allow water to flow through more than one showerhead or from body jets. But the biggest problem for you right now probably isn't cost. To install another valve, a plumber would have to cut into the wall – which people who have just renovated probably don't want to do.

Do you have a problem in your home? Send questions to [email protected]. Type “How To” in the subject line, tell us where you live, and include a photo if possible.

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