February 2010 - Hot Water Temperature

Heating water is one of the biggest users of energy in a house. We have a large storage gas hot water system. This means that it works all day to keep the 135 litres inside hot and ready to use. This month's sustainable action was to reduce the temperature that the water is heated to and stored at. As I sit to write about how much effort it took and how much impact it has, I can't believe we didn't do it sooner. The water is still easily hot enough to have a great shower, even on a cold morning (not that we have had many of those in Perth this year).

Initial Cost: zero

Initial Time: five minutes

Ongoing time or cost commitment: zero

Impact: I thought there would be a nice easy calculation for this - an equation of 'water takes x units of energy to heat to y temperature therefore a reduction of z degrees means an xyz reduction in energy usage'. Tyson sighed at me and said its not as simple as that. Each brand of water heater uses a different amount of energy when new, and then it depends how old the system is, whether we use our hot water all in one go or in little bits through the day, where the system is located (if its in the sun, it stays warmer. Duh. Why didn't I think of that?), what the climate is like, and so on. Also when we opened the box we found the dial didn't say what actual temperature it was set to. It was on the highest one - at a guess probably about 70-80 degrees C. We turned it down from '5' to '3', which we guessed would be about 60 degrees C. (It's not safe to store hot water at less than 60 degrees C as there is a danger of legionellas breeding)

BUT: Our recent gas bill was about one third less than the same period last year, and we only use gas for cooking and hot water, so even without a clever formula I can say that it is making a big difference!