Drain Water Heat Recovery Systems
What happens to your hot water once it goes down the drain? For most homes, that answer is simple, the hot water goes down the drain and into either the sewer or the septic system, never to be seen again. All the energy spent to heat that water is wasted once the hot water has fulfilled its purpose and gone down the drain. That seems like such a waste. Thankfully, there is a way to use some of that heat going down the drain. It’s called a drain water heat recovery system.
What is a Drain Water Heat Recovery System?
A drain water heat recovery system is a heat exchanger that is installed in the drain line of your home. Usually downstream from a shower or tub. These devices were first introduced back in the 1980s to reduce water heating costs up in Canada.
The drain water heat recovery system is comprised of two parts, a copper main drain line to replace the existing cast iron or plastic drain and a wrapped copper coil.
Image from energy.gov
How does a Drain Water Heat Recovery System work?
First, let us go over how your hot water system works without this device installed. Cold water from either a well or a municipal water supply comes into the home. This cold water supply is piped to your water heater. Your water heater will now heat that cold water so you can have hot water for your shower. You turn on the shower, hot water comes out and goes down the drain.
Now, with a DWHR system, things are a little different. Your cold water supply that goes to your water heater instead goes to the heat exchanger first, then your water heater. When you take a shower, and your hot water goes down the drain, that hot drain line transfers heat through the heat exchanger and into the water entering your water heater. This is called tempering or preheating.
The DWHR system tempers the water going into your water heater. When warmer water enters the water heater, less energy is needed to heat that water back up to the temperature your water heater is set.
Is a Drain Water Heat Recovery System worth it?
There are a few factors that need to be taken into account before deciding if a DWHR system is worth it for you in your home. One of the largest factors is the orientation of your drain piping in the home. a DWHR system works best with vertical drain lines, and they come in sizes around 48” to 60” in length. There are horizontal style systems, but they are less efficient as drain water in a vertical application clings to the surrounding pipe, and a horizontal drain line has all the hot water at the bottom of the drain line.
Another factor is the location of the drain compared to your water heater. Sometimes the water heater is installed on the other end of the home from where this device would be installed—increasing your internal piping by a large amount. That can be an issue if you now have to run extra piping through finished sections of the home as well.
However, in lieu of those factors, a drain water heat recovery system is absolutely worth it. Getting back the heat from drain water to temper the supply to your water heater has been shown to reduce energy costs from water heating by up to 40%. Depending on how you heat your water, this has a potential payback between 3-8 years.
With no moving parts and no need for maintenance, this is a device you install and never have to think about again. All the while, it’s saving you money by reducing your water heating costs. If you have the drain line available in your home to use this system, there is no better choice.
Have you installed one of these already and want to take your home to the next level? Our Online Energy Audit is just the thing to continue in your journey to be more energy efficient and fight climate change. Want some more saving tips instead? Check them out here.
