[Footprint] Hot Water and Showering

We've recently had a new shower fitted that has a thermostatic mixer tap so that hot water from our combi boiler (that only heats the water that is needed when you turn a hot tap on) mixes with cold water supply to give you water at the temperature that you want. The great thing about it is that you can turn it on and off, easily, without suffering any cold or overly hot water when you turn it back on. This means that when putting shampoo in your hair or using soap on your body you can turn of the water and save water and save energy not heating that water.

Another consideration that has come to my attention about showering is whether you should heat up your shower room (or bathroom) before your shower as this may mean that you don't need to use so much water at such a high temperature - saving energy. So is it worth heating up the air and saving on water heating?

Let's think of this in terms of energy used:
A typical bathroom might be 2.5m x 2m with a height of 2.4m - a volume of 12m3 (12 cubic metres).
To heat the air in this bathroom from 14C to 27C (a comfortable bathroom temperature) takes 191kJ (kilojoules) (excluding inefficiencies).
The other option is to run the shower at around 45C for the whole showering time instead of around 38C and just running the water when you need to rinse. Assuming that the water starts at about 8C when it enters your home these are rises of 37C and 30C respectively.
Total shower time is approximately 8 minutes and the water flow rate is about 4 litres per minute. Therefore the 45C method using water for the whole 8 minutes uses 5,000kJ of energy (excluding inefficiencies).
If you turn the water on and off you probably use about a third of the water (2 mins 40 seconds) and at 38C your energy use is 1,340kJ.

The conclusion therefore is that if you heat your shower room fully and turn off the shower when you are not rinsing yourself then your total energy use is 1,531kJ, but if you don't have a fully warm shower room and instead just keep running the shower the whole time you use around 5,000kJ of energy. So you can reduce your energy use by 70% while you shower! Naturally this has a knock on effect of reducing your showering related CO2 output by 70% also.

Please note that you do need to ensure that you, personally, are warm before your shower, as otherwise you will still feel cold even if the bathroom is at 27C. Also, this is just a small saving that needs to be part of a more efficient lifestyle such as keeping the temperature of your home at perhaps 20C during winter instead of 25C, ensuring that your home is well insulated and using your car less.