As you are showering, do you ever wish there were a way to capture and reuse some of the water and heat you are running down the drain? There is a way to salvage the heat energy used for showers, washing dishes, doing laundry … anywhere you use hot water.
The Department of Energy (DOE) estimates that
80-90 percent of the heat from hot water is wasted; that’s the equivalent of 350 billion kWhs worth of hot water literally running down the drain each year. A large portion of that is recoverable. In fact, the DOE ran tests on a product that successfully does just that. The
Gravity-Film Heat Exchanger (GFX) was developed by a grant from the DOE and is commercially available. The DOE estimates that consumers can save up to 50 percent of the heating energy required for a shower and will also save wasting water because water coming from the showerhead will heat much faster. The unit also shortens the time needed for a water heater to recover, so you won’t run out of hot water as quickly.
How it works
In a nutshell, the unit replaces a section of piping and transfers the heat (but none of the actual wastewater) from water running down the drain to cold water moving up to the shower (or dishwasher or clothes washer). The unit has the ability to increase water heater capacity and allows you to turn down your water heating temperature.
The units work best on electric storage and solar water heaters, but GFX says that you can benefit if you have a tankless, gas, or oil heater, too. A unit can triple the shower capacity of an electric storage water heater (while halving the cost of a shower). A study conducted by Old Dominion University found that GFX boosted first hour ratings on high-efficiency 50-gallon electric water heaters from 60 to 180 gallons.
The cost of a small unit for residential units is $500-$600; payback time depends on the amount of hot water you use. GFX states that if adding one of these units keeps you from having to purchase a larger water heater, your savings start immediately. Energysavers.gov estimates payback at 2.5 to 7 years, depending on how often the system is used.
Comments from an informed user
Jean Eels, E Resources Group, Webster City, provides education on the environment and energy, and also provides home evaluation services. She has installed a wastewater heat recovery unit on the pipes exiting their shower. She is not an expert on the product, but provides her thoughts as a consumer:
- It’s possible to purchase either a whole-house unit or a smaller unit for a particular application (such as at the shower pipe or kitchen sink).
- She says, “We have ours under the shower—the rationale being that the hot water is actually running for a few minutes and there’s time for the heat transfer to occur. She also notes that in their household, the shower accounts for about 30 percent of the hot water use in the home.
- She does feel a difference in the shower. “You turn it on and fairly shortly after you get in, you’re turning the hot water down.”
- She suggests that placement under a kitchen sink might also make sense, because cooking and cleaning up “involves several pulls of the faucet, so the water in the coils and the drain would have some time to heat up.”
- Jean has checked the system “using one of the little infrared heat guns to read the temperature on the cold water coming in at the bottom of the unit and then near the top of the unit. There’s definitely a temperature difference depending on what it comes in at.”
- Before buying, she recommends making sure your plumbing can handle the unit. It will “affect the fall of the drain, so it has to be higher than the waste drain going out of your house. It may involve some replumbing.”
- Her overall comment on the system is that it's “pretty nifty.”
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