Don't let heat go down the drain

“What are these?” came the shout from the bathroom.

It was my wife asking about the electronic sensors I had stuck to the shower wall – doesn’t everyone?

They were actually digital temperature monitors – one attached under the showerhead, the other stuck down the drain as I wanted to see how hot the waste water was.

It's not something I do every day but, having found some interesting products designed to recover heat from the shower waste water, I wanted to get some figures to work with.

The results were interesting: Shower temperature 39°C, waste water temperature 36°C.

So we (and everyone else) are heating the water for our shower and the water going down the drain is still hot and that is heat energy which we are wasting.

Shower water is still hot when it flows into the drain and the same is true of the water used for washing machines, dishwashers etc.

So, as the waste water was only slightly cooler than when it came out of the showerhead and we should be able to recover some of this heat energy and use it.

If we ran this hot waste water through a copper tube the copper tube would get hot – and if we then put this copper tube in line with the cold water feed to our hot water cylinder (preferably a solar cylinder) it would pre-heat the cold water going into the cylinder.

The end result is we have recovered some of the wasted heat and are using less energy to heat up our water.

While you shower the hot water cylinder is constantly being topped up with cold water but now the water will be coming in at a higher temperature than from the mains – simple.

The waste water never comes into contact with water in your cylinder so there is no chance of contamination.

Interestingly more than 20% of new houses in Holland now incorporate such a system which is helping the country to meet environmental targets.

It also has no moving parts so the products available should last a long time.

Still on the shower theme, shower timers are very popular in Australia where showering accounts for 30% of home water use.

Shower timers are set for four minutes and have dramatically raised awareness of water conservation.

Lastly, new TV ads in Brazil are encouraging people to save water by urinating in the shower.

Brazilian environmental group SOS Mata Atlantica says that if a household avoids one flush a day, it can save up to 4,380 litres of water a year.