The overwhelming majority of water heaters are not set properly. Many homeowners set their water heaters far too high for a variety of reasons. Some think it’s so they can use less hot water at a time to achieve their desired temperature. Some think it’s healthier to use hotter water. Regardless of why, the truth of the matter is that setting your water heater too high can be dangerous for you and your home as well as bad for your energy consumption.

What Happens When Your Water Heater Is Set Too High?

The overwhelming majority of water heaters that we see are set above the recommended temperature levels. There are plenty of reasons for this. First, many people believe that by setting their water to a hotter temperature, they can use less hot water to achieve their target temperature. This means longer showers and shorter water heater cycles. However, this isn’t the case. Running your water heater too high actually makes your water more vulnerable to losing heat as it travels through your hot water pipelines. The greater the temperature difference between the water in your lines and the ambient temperature around the line, the more likely it is to lose heat (especially with metal hot water lines like copper). You do save a bit of hot water, but in reality, it isn’t all that much unless all of your hot water lines are properly insulated.

Second, running your water too hot leaves you vulnerable to serious injury from a hot water burn. It takes only two seconds of exposure to 150-degree water to cause third-degree burn injuries on bare skin, and that means accidentally sticking your hand or foot into a shower at that temperature could cause a devastating and extremely painful injury. At 140 degrees, the same injury takes only six seconds, and at 130 degrees, it takes 30 seconds. And you never know when someone in your house might flush a toilet and cause that comfortable shower to suddenly surge to scalding temperatures.

What Happens When Your Water Heater Is Set Too Low?

Setting your water heater too low leaves you vulnerable to a different problem: energy waste. When your water isn’t hot enough, you will have to utilize more of it to reach your desired temperature, thus leading to a lot of hot water waste. While this water will lose less energy in transit, the fact that your shower or load of laundry will require more hot water means your water heater will drain faster, and that means you will have to refill it and reheat it more often. Reheating an empty water heater from an ambient, cold temperature takes longer and uses more energy than partially refilling and reheating the tank (and it causes more wear and tear on the heater itself).

How to Properly Set Your Water Heater

According to the US Environmental Protection Agency, the optimal temperature for a water heater in an average home is 120 degrees. This keeps your water below the point where it can accidentally scald skin and cause injury. This also helps you avoid excessive hot water use and the excessive energy reheating can require. However, this temperature is not ideal for every home. Generally, 120 degrees is the maximum temperature that several types of bacteria like salmonella or legionnaire’s disease can exist in. And because many of these bacteria can be easily transmitted through water, it makes sense to keep the water a little bit warmer.

At-risk individuals, including seniors, infants or babies, or those with skin or immune issues should set their water heaters to no higher than 130 degrees. While exposure to a full blast of water at this temperature can cause injury, it does so more slowly and gives you time to react and get away from the water.

Finally, those with respiratory issues or who desire a greater quantity of steam during their showers should consider setting their thermometer to as high as 135 degrees. The added steam is great for health, but it does come with risks. We don’t recommend this for larger homes, homes with high populations (particularly with young kids who might flush the toilet while someone else is using a shower), or for those who are in good health, as the burn risk can be higher. But so long as you use enough cold water to compensate and keep water temperatures reasonable, this temperature level can still be safe.