How to Determine the Ideal Temperature Setting for a Hot Water Tank Thermostat?

September 25th, 2019

Why are hot water tank thermostats set at higher temperatures? For once, here’s a simple question to answer. It’s because of system contaminants. No, not the hard water minerals that leave scaly rings around everything. It’s the bacteria that would otherwise thrive in warm water. Hotter than 60°C, harmful microbes can’t survive in steamy hot water. Of course, the water can’t be allowed to scald bathers either.

Finding Tank Thermostat Sweet Spots

At the lower end of the scale, that 60°C mark, bacterial threats can’t endure. That’s a known safety feature, one that protects you from unsanitary threats. Waterborne microbial pathogens, including legionella and pseudomonas aeruginosa (swimmers ear), can take hold in hot and humid settings. That’s why your water is hot, that and the fact that you like a nice hot bath or shower. Then, to eliminate scalding hazards, the thermostat locks in an upper-temperature threshold as well. This upper limit locks in at around 65°C. In general, your heating engineer will use the 60°C – 65°C tank temperature sweet spot to keep you hot but safe. Meanwhile, the same optimized thermal spread keeps microbes out and your fittings corrosion-free.

Dropping the Low-End Limit

Let’s say a service engineer has recently inspected your hot water tank. After talking matters over, he drops the lower limit an additional 5°C. Why has he done this? Well, the water’s still hot, that’s the good news. But while this lower limit was just on the verge of being too hot, now it’s in the “Goldilocks Zone.” It’s hot but not too hot for a young child, who might have delicate skin. Also, if there’s a high concentration of hard water in the mains line, the lower temperature threshold will prevent scaly build-up and corrosion damage. Remember, this alteration to the thermostat isn’t always necessary, but it’s a good idea to make the change if the two conditions mentioned above are present. As a rule, young children and hard water areas require slightly lower hot water temperatures.

Finally, don’t set the upper level too high. Sure, the equipment usually incorporates special mixer valves, which exist to prevent scalding. All the same, that upper limit must never be raised too high. Besides, by keeping the hot water tank locked at 65°C, you’re saving energy. When you save heating energy, you’re also saving money. The only time a service engineer might raise the upper limit by a few degrees is if one of a handful of unique conditions is met. A suppressed immune system, a higher than normal microbial contaminant rating, or a heat-resistant strain, these are a few of the rare reasons for raising the ideal temperature setting of a hot water tank’s thermostat.

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