Do kettles boil at 100 degrees?

It may surprise you to know that kettles do not always heat water to 100 degrees Celsius. We briefly covered the topic in our recent kettle facts post, but we will now expand on that.

Ideal Temperature for a Hot Drink

Ideal is subjective, but anything around 80 degrees Celsius is perfectly acceptable for a hot drink. Some kettles, but unfortunately not all, allow you to choose your own temperature. These are particularly useful because heating water to 80 degrees Celsius is cheaper than heating water all the way up to 100 degrees Celsius, even more so when taking into account the number of times the kettle is used.

Why does water boil below 100 degrees Celsius?

By this we're not talking about the slight variation you get with altitude changes (we will get to that). We're talking about why, when the water is clearly below 100 degrees Celsius, you see steam and bubbles.

Answer: Kettles do not heat water uniformly. Put simply, kettles heat water at different temperatures in different places. Water around the heating element will be far hotter than water near the surface. You are therefore seeing some of the water boiling, but not all of it.

Does the boiling point change with altitude?

Yes. Generally the rule is, the higher your altitude, the lower the boiling point of pure water is. At sea level (0 metres), boiling point is, by definition, 100 degrees Celsius. Consider these examples:

1. 1,000 metres below/above sea level. 1,000 metres below sea level pure water will boil at 101.1 degrees Celsius. 1,000 metres above sea level pure water will boil at 98.8 degrees Celsius.

2. Countries. The United Kingdom is on average 162 metres above sea level. Pure water will therefore boil at 99.5 degrees Celsius. On the other hand Bhutan, a country in South Asia, is a whopping 3,280 metres above sea level. Pure water will therefore boil at 88.8 degrees Celsius.

3. Mount Everest. At 8,848 metres above sea level is the peak of Mount Everest. Up there, pure water will boil at 72.0 degrees Celsius.

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