Throwing Water Down the Drain: Simple Steps for Heat Recovery


Many of us turn a few knobs and, miraculously, hot water comes out without much thought other than our energy and water bills. However, the water that ends up in the drain retains a certain about of embodied energy that is capable of being recovered. This water is now technically graywater, but you’ve paid valuable money for the energy used to raise its temperature. It makes sense to recapture this energy and there are a few great products that can help with this.

Heat recovery is nothing new, however it is becoming more main stream and affordable than ever before. If you’re looking to cut a few bucks out of your energy bill while looking for a relatively easy way to help make a bigger impact on your regional energy footprint, then a small addition to your water circulation lines may be the answer.

Large-scale buildings implement large-scale heat recovery units which are mechanical systems that extract the remaining heat energy from already heated water once it’s past through a building’s heating system. When applied at this scale, this strategy can provide tremendous savings. While larger buildings consume an overwhelming proportion of energy, a growing population means increased demands at both global and regional levels. Achieving our energy independence goals will require infrastructural change at the federal level, however, we as home owners can make a significant contribution to this effort by adjusting a few priorities without breaking the bank.

Showers, bath tubs, and sinks are a prime example of wasted heat energy. For example, showers use water stored in a hot water tank that is typically heated by natural gas, oil or electricity to a high temperature of 77° F. This may not seem that hot, but this can be 20-30 degrees warmer than the water coming into your building from the city supply. This water is then rinsed over the body at 13 – 21 gallons per minute (10 minute shower = 210 gallons!), depending on the fixture (which can be as low as 1.25 gallons per minute) and enters directly into the drain. This heat energy should be headed back to your hot water heater rather than out to the street’s waste water line.

Below is a diagram of a typical hot water loop. Notice the potential for transferring hot water energy from fixtures into the cold water supply line before it enters the hot water heater.


A company called Ecodrain has created a sleek apparatus that can be installed to do just this. Heated graywater transfers it’s heat energy to fresh potable water as one leaves the system and the other enters. The two streams never actually mix and only heat energy is transferred. This raises the temperature of potable water as it enters the house so the hot water tank uses less energy to raise the temperature. These systems are now available for residential use and claim to have a short-term payback of only a few years.




Have you installed a similar system in your home? Have you noticed any savings? Comment below and let us know if heat recovery is making a difference in your life, or if you think it’s a complete waste.


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