Draining Heat

On a cold day in winter time, in almost every northern city, you'll see steam rising from the slots in manhole covers. This is caused by warm water flowing down sewers and this heat is being paid for by you and me.

After a long bath - or a washing clothes in hot water - the water that leaves the tub is still very warm. In fact it stays warm right into the sewer.

Taking a page from heat recovery air exchangers a new invention takes the hot water going down the drains and uses the heat to to take the chill of of the incoming ground water. This is the water that comes in from the city service or well that is around 40 degrees Fahrenheit and takes a lot of energy to heat up to 140, which is the default of the hot water tank.

How this system works is that a long copper drainpipe, between three and five feet is spliced into the the drains (shower, bath, dishwasher etc.). Copper pipe (1") is tightly wrapped around each long copper drain and absorbs the heat from the draining water. The input of this coiled 1" pipe is the cold water intake and the outlet goes into the cold water tap of the shower. The result is that soon as the water in the shower heats up it does not take as much hot water to have a hot shower.

If you have a basement you could hook these drainpipes in series to the main cold water intake as it enters the water tank thus taking a lot of pressure off the water tank element and saving money daily.