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# Getting into hot water

Continuing the ‘what’s it cost’ theme, I thought I’d write a quick post about how much hot water costs…

It turns out a normal kitchen sink, at a normal hot-water temperature costs almost exactly One Rand *(in 2014)*. Here’s how we get to that…

Just multiply the LITRES of water by the TEMPERATURE that it’s increased by (in Celsius) and then divide that number by 860*. Cold water is normally around 10 degrees – so just take away 10 from the temperature of your water to get the temperature change. This gives you the number of kilowatt-hours (or energy units on your prepaid meter) – so now you just multiply that by the amount you pay for each unit. For most people this will be somewhere between R1.00 and R1.50

A sink is normally around 10 litres – if you don’t believe me try it with a measuring jug sometime!

Normal hot water is 65 degrees – whereas cold water from the tap is about 10 degrees, so the temperature INCREASE is 55 degrees

10 x 55 = 550 litre-degrees

550 / 860 = 0.639 kwh

Eskom Homelight users pay R1.62 per kilowatt hour for an extra unit

0.639 x 1.62 = 1.03c

That’s pretty close to a Rand if you ask me 🙂

* – for any geeks out there, that’s because we’re multiplying by the specific heat capacity of water (around 4200 Joule per kilogram-degree, for liquid water, most of the time… don’t ask!), then dividing by 3,600,000 – the number of Joules in a kilowatt hour; which is basically the number of seconds in an hour times 1000.

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