What’s The Ideal Temperature For Hot Water At Home?

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We've all experienced similar situations. One day, we turn on the faucet only to burn our hands with scalding water. It's days like these that make us question if we are using the ideal settings. What should the temperature for hot water be at home? If that's your concern, let's go over the details.

The ideal temperature for a water heater depends on several factors. If you prioritize cost-efficiency and comfort, 120 degrees Fahrenheit is ideal. A setting of 125-140 degrees is best if you have a suppressed immune system. Both settings have advantages and disadvantages.

No one enjoys using hot water that can scald hands. Though, it's equally dangerous to mess with settings if you don't have a reason. A temperature range between 120 and 140 degrees might seem high. But, there are issues that each setting addresses. To learn more about the topic, keep reading. 

Water heater adjusting knob on the side of the boiler, What's The Ideal Temperature For Hot Water At Home?

The Ideal Temperature For Hot Water

The purchase and use of a water heater comes with many responsibilities. One of them is choosing the ideal temperature. So, you might be curious to know why 120 and 140 degrees are optimal. 

In most cases, people go with the default settings. Therefore, the water heater is likely at 140 degrees Fahrenheit. It raises the question, why would manufacturers pre-set it to 140? 

A faucet pouring hot water

The answer would have to concern Legionnaires' disease. It's a form of bacterial pneumonia. If it manages to grow in your water tank, water will carry it throughout the plumbing. 

When you take a shower, it will become airborne through water droplets. Inevitably, you'll inhale it. It's a serious disease that kills 1 out of every 10 people who get sick with it. 

Who Are The Most At Risk For Legionnaires Disease?

A specialist holding a vial of legionella

According to the CDC, most healthy people will not get sick after exposure to legionella. If it manages to infect you, you will most likely need to visit a hospital. Though, most people will recover from it. 

There are a few groups that are most at risk. People older than 50 years old are one of them. Current and former smokers are another group. The latter group includes people with a suppressed immune system. 

If you suffer from a chronic lung disease, are taking cancer treatment, or are suffering from diabetes, you shouldn't take legionnaires disease lightly. 

For this reason, manufacturers and plumbers alike recommend maintaining high temperatures. Legionella thrives in temperature ranges around 77 to 113 degrees Fahrenheit. A temperature setting of 140 eliminates this threat. 

Disadvantages of 140-Degree Setting

But, how crucial is eliminating the threat of Legionnaires' disease if we increase another risk? More specifically, maintaining a temperature of 140 degrees can cause burns and scalding injuries.

Of course, you could say that it's an avoidable situation. But how confident are you about keeping an eye on children, elderly family members, or disabled housemates? 

These three groups are more susceptible to burns from scalding hot tap water. It doesn't take much time for burns to occur. In fact, it takes as little as 2 seconds if the water temperature is above 140 degrees Fahrenheit. 

The Case for 120-degree Water Temperature

Now, we know the factors we have to consider. No one should take Legionnaires' disease lightly. In similar thoughts, scalding injuries are equally worrying. 

So, if 140-degree Fahrenheit water can be dangerous, where does that leave us? As we've learned, legionella thrives in temperatures around 77 to 113 degrees Fahrenheit. So, we want to keep it above 113. 

Some would suggest 120 degrees as the best compromise. Even the Department of Energy recommends it. However, they mostly look at the cost-efficiency angle. A water heater set at 120 degrees Fahrenheit can save you more in the long run. 

The Risk of Lowering the Water Heaters Temperature

A setting of 120 degrees is above what legionella can handle. Unfortunately, sometimes it's not enough. There's a slight risk of promoting legionella bacteria at this range.

The setting is enough to stop the bacteria from multiplying, but it doesn't kill it. At best, it inhibits it from spreading quickly. Of course, other factors affect the bacteria's growth.

Temperature is only one of them. If we want to get into the specifics, three more conditions promote its growth. The bacteria favor slow-moving or stagnant water. 

Of course, inadequate levels of disinfectant increase the chances it shows up. The presence of sediment, scale, or biofilm also promotes its growth. If you can keep these factors in check, a setting at 120 degrees Fahrenheit should work.

Which Setting Should You Choose?

The situation brings us to a dilemma. Should you lower the temperature, which doesn't kill legionellae bacteria? Or, do you keep the water heater at 140 to eliminate the deadly problem?

Fortunately, you have options! Scalds aren't a problem to take lightly. However, it's easy to prevent a scald injury. On the other hand, Legionnaires' disease is far more tricky. 

Thermostatic Mixing Valves

A brass connecting pipe on a white background

Since we want to keep Legionnaires' disease at bay, it would be best to leave the water heater at 140 degrees Fahrenheit. This temperature is high enough to kill most harmful bacteria. 

So, the source of our home water will generally be safe. Now, we have to think about the point of delivery. If we don't want to burn ourselves with hot water, we would need to change the temperature at the faucet or shower. 

Click here to see this thermostatic mixing valve on Amazon.

One way you could do that is through a valve. Various valves mix hot and cold water to reduce the temperature to a point it won't scald you. The most effective one is a thermostatic mixing valve.

Click here to see this thermostatic mixing valve on Amazon.

This valve will allow you to keep the water heater at a higher temperature. But, once you open a faucet or shower head, it will mix hot and cold water to lower it to a favorable setting. So, you can have hot water at 140 degrees in the tank and 120 degrees at the outlet. 

What Are The Alternatives To A Mixing Valve?

Turning on the water heater inside the bathroom

Some people may not want to mess with their plumbing. Maybe you're having a tough time, and installing a valve isn't in your budgeting. So, are you forced to choose between scald injuries and Legionnaires' disease? Not exactly!

While 120 degrees Fahrenheit isn't enough to kill the bacteria, it isn't far from that goal. Legionella isn't hard to kill. Yes, it can survive at 120 degrees. But, turn the setting 5 degrees higher, and it will die in minutes.

So, if you want to reduce the risk of contracting this disease, you can set it at 125 degrees Fahrenheit. Of course, you can go higher than this. Other suggestions include setting the water heater at 130 degrees Fahrenheit.

The Case For 125-130 Degrees

Although, the higher you go, the more likely someone vulnerable in your home will suffer burns. 125-degree water seems to be a comfortable setting on all fronts.

According to the American Society of Sanitary Engineering, it would take around 1.5 to 2 minutes to suffer scald injuries at 125 degrees Fahrenheit. That's enough time for any person to react. In comparison, temperatures around 130-140 are more dangerous.

At 130, it would take 30 seconds to suffer burns from hot water. At the recommended temperature of 140, it takes less than 5 seconds. If you're hesitant, 130 degrees Fahrenheit would also do well. Though, you'll have to warn others about the temperature changes.

This way, they know beforehand how hot the water can get. You'll mostly want to focus on children, the elderly, and the disabled. They are the most at risk for scald injuries.

How To Prevent Scalding

Woman adjusting the water heater level

At times we've run the hot water only to burn our hands at first touch. It's a learning moment for everyone that our tap water can harm us. So, how can we prevent it from happening again without messing with the water heater?

There are simple actions you can take to prevent it from happening. The first is to test the waters before you use it. Whether it's for household cleaning or baths, check the temperature of the water first.

If you have to fill an area with hot water, consider using cold water first. Let it fill the bucket, tub, or sink for a few inches before using the hot water. Of course, dip a finger into the water to see if it's at a comfortable level.

Consider Temperature Changes

When you run hot water, it won't burn you immediately. The danger lies after letting it run for more than a few minutes. Initially, it may feel comfortable at first touch. But, it will get hotter if you let it run.

So, you would also want to turn the cold tap on a bit to get a comfortable temperature. You don't have to turn it on all the way. However, a light turn will prevent the hot water from reaching scalding temperatures.

In this situation, you're acting as the mixing valve.

In Closing

Water heater adjusting knob on the side of the boiler

It's always good to know the reasons behind a decision. As we've learned, a water heater should be at a high temperature to prevent bacterial growth. Although that comes at the risk of burns. What setting will you go with?

Before you go, do you have other water heater concerns? Are you looking for the signs of one that has gone bad? To learn more, check out:

What Happens When A Water Heater Goes Bad?

For information on how long a water heater lasts, check out:

How Long Does A Water Heater Last?

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