How to Keep Hot Water Temperature at the Safe Level
(updated 2018)

When talking about the safe use of the water heater, hot water temperature is the topic that is not analyzed enough.

We are warning about the importance of that matter by specifying two opposite situations: Insufficiently high temperature inside the water heater tank increases the risk of multiplication of very dangerous bacteria. On the other end, hot water that is too hot can cause at the moment of inattention, equally dangerous scalding burns, especially in babies and toddlers.

What, then, is the temperature at which water should be kept so that it is safe?

Here, we are answering this question in consultation with experts, emphasizing that there are well-designed products on the market to solve the problem effectively.

Which hot water temperature is the best?

If you use a tank water heater, water temperature in the tank must be high enough to guarantee its cleanness and safe for healt. Standing water is a suitable environment for bacterial growth and the most known is Legionella pneumophila, which if inhaled can trigger a serious lung disease (Legionnaire's disease).

The best condition for Legionella multiplying is water temperature of 30-40 degrees Celsius. Experts have concluded that the minimum recommended temperature of the water inside the tank is 60 degrees, accordingly, many counties including Canada and USA set 60°C as a standard in the plumbing code and regulations.

But how to achieve the recommended 60 degrees Celsius (140°F) and be sure that the temperature will be maintained at a given level? The modern systems are equipped with a designated regulator. Hot water tanks are particularly well insulated and significant heat loss through the storage wall is prevented, even at low energy consumption.

Additional measures may include draining the pipes after a multi-day pause in using the water heater, and checking the temperature at each extraction point.

The occurrence of Legionnaire disease is rare, but not the scalds.

As long as the scalding burns are small, we do not take them seriously enough. When severe tissue damage occurs and the treatment becomes long-lasting and painful, one realizes that hot water is very dangerous. Hot water is especially dangerous for children, elders, and people with disabilities, therefore we remind you of some important data.

Water with the temperature of 60 degrees Celsius (140°F) causes scalding burns of the 2nd and 3rd degree when adult skin is exposed for only 5 seconds. Unlike first-degree light burns, second-degree scalding burns are moderate. The top layer of the skin is destroyed and it is recommended to consult a doctor, as there is a risk of infection.

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A third-degree burns destruct all skin layers. They are not curable. The nerves are equally destroyed. Third-degree burn is always framed by first and second-degree burns. An immediate visit to a doctor requires every third-degree burn, second-degree burn if it is larger than a palm, and any large scale first-degree scald.

Second and third-degree scalds occur when the skin was exposed 30 seconds to the water of 55 degrees Celsius (130°F) for 30 seconds or to the water of 49 degrees Celsius (120°F) for 5 minutes. Taking into account that children's skin is more sensitive, only the temperature of 120°F is considered safe, hence the plumbing rule says – water at the tap outlet should not be warmer than 49 degrees Celsius.

What is a solution for two different demands – 60 degrees in the water heater tank and 49 degrees on the faucet? Or, how to keep water safe and prevent scalding burns?

Solution – mixing valves

Thermostatic mixing valveThermostatic mixing valve

At this point, we suggest contacting a qualified plumber, who will check your water heating system and propose the type of mixing valves to control the tap water temperature.

Overall, there are two major groups of mixing valves.

Devices in the first group (anti-scald mixing valves) are to be installed at or near the water heater, heating boiler, tankless coils...

In the second group, there are mixing valves which are designed to be installed at the point of use: faucets, tubs, showers, sinks... (pressure-balanced and thermostatic mixing valves). Devices mix cold water manually or automatically. The plumber will explain you everything important to know. The main principle of operation of these devices is blending hot water with cold water to get the safe temperature level.

If you live with a child, an elderly person, or a member of a household with limited ability to take care of himself, let the plumber set maximum temperature to be lower than the standard one (38 °C / 100 °F may be a safe choice).

Please note that there is quite a lot of confusion in terminology on this field – it is not clearly defined what names are used for which type of valves, so it is easiest to refer to the place where the valve is to be mounted – at the heat source, at point-of-use or for group of outlet fixtures. Some models of the water heaters come with the integral anti-scald device.

So, if you want to protect yourself and your family from bacterial infection and scalding burns at the same time, consider installing devices which will control water heater temperature inside and outside of the appliance. It will be an additional expense but aimed to prevent many unpleasant situations and worries.

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