Optimize your boiler's tap water temperature
Your shower doesn't need to get any hotter than the temperature you like to take showers. So, in an ideal world your boiler would heat the water to the perfect shower temperature, then when you had a shower, you'd turn the tap to hottest and get the same perfect temperature every time.
Unfortunately we live in a non-ideal world with legionnaires' disease in it — and so the lowest temperature you should safely set your boiler's tap water to is 50°C/120°F or 60°C/140°F if you have a storage boiler (more on that below.)
Setting your boiler to the recommended lowest temperature can save you money, reduce wear on your precious pipes, and reduce the risk boiling yourself.
Important safety warning
It's important to know that reducing your boiler temperature below 60°C/140°F could be unsafe if you have a storage boiler. A storage boiler stores hot water rather than heating the water only when needed.
Legionella bacteria can grow between 20°C/68°F and 45°C/113°F.1 Legionella is killed in temperatures above 60°C/140°F.2
Legionella causes legionnaires' disease. It can be fatal especially for people with compromised immune systems or chronic respiratory issues.
Understandably, most organisations are cautious when giving advice on how low you can set your hot water temperature – and do not deviate at all from health guidelines.
However, the US department of energy suggests most households can safely set their water boiler to 50°C/120°F — even if it is a storage boiler.3 Importantly, they note that if someone in your household has a suppressed immune system or chronic respiratory disease, you should maintain the temperature at 60°C/140°F.
How to tell if you have a storage boiler?
A storage boiler's minimum safe temperature is 60°C / 140°F but a non-storage boiler can safely be set to 50°C / 120°C. It's important to find out which one you have so you can save money while avoiding death.
Boilers that store water are usually obvious as they have a big cylindrical tank. If your water boiler has one of these tanks then it stores heated water.
If your boiler is a box on the wall or in a cupboard, it is probably the type of boiler that heats water on demand. However, some of these also store water so if you can't see the tank, it's worth googling the model of your boiler and checking.
How much money can you save?
The actual amount of money you can save varies wildly depending on your behaviour, the size and efficiency of your home, the current temperature of your boiler, and the whims of world leaders.
The U.S. department of energy estimates you could save between 4%-22% of your energy bill.4 So potentially quite a lot.
What about hot water for heating the home?
In the UK pretty much everybody's home uses a boiler to both heat the home and for showers and baths. This is usually called a combi boiler. They're also popular in the USA but many people have electric heaters, or furnaces that heat the home with hot air.
If you have a combi boiler you can save even more money by adjusting the temperature of the water it uses to heat your radiators. See the previous practical betterment: Adjust the temperature of your boilerFootnotes