ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Sustainability 68: Drain Water Heat Recovery

Updated on May 16, 2013
Don't throw away that heat!
Don't throw away that heat! | Source

In our efforts at energy conservation and sustainability, many of us keep seeking newer and more innovative ways of eliminating or capturing wasted energy. One of those cutting-edge methods — long in use in areas of very cold climate — is the recovery of the heat embodied in draining wastewater.

The concept of Drain Water Heat Recovery (or DWHR) is quite simple. The heat that is embodied in water draining from showers, tubs, dishwashers, laundries, sinks and other such appliances and equipment is retrieved as that water travels through wastewater drains and sewers, and is then reused to pre-heat incoming cold water. While DWHR can appear initially most cost-effective in large-scale commercial or institutional facilities like prisons, hospitals, schools, recreational facilities, and multifamily residential structures, it can also prove efficient even in a single-family home or condominium.

The prime attraction of DWHR lies in a vast untapped energy resource. In many of our structures, the heating of water for personal, commercial or industrial use is typically the second largest energy consumer. As our homes and other buildings become ever more energy efficient as thermal envelopes and air seals, water heating may in fact rise to the greatest single consumer of energy in structures. It is estimated that up to 90% of the heat embedded in the water we use is not ‘consumed’, and remains in that water as it drains away. The potential for energy recovery is therefore significant.

Savings are realized in the substantial reduction in energy used to initially heat incoming cold water. (In effect, the hot water you used several hours ago pre-heats the next batch of cold water you wish to use hot several hours from now.) DWHR not only increases the effective hot water capacity of a system (by continually reusing the same heat, and thus ‘cycling’ faster), but also extends the life of hot water heaters by damping down their operation.

In commercial and institutional structures, DWHR can reuse the heat from draining dishwashers, clothes washers, saunas, spas, showers, and sinks, whereas most residential heat recovery is from showers. DWHR is most often designed into a facility during construction, as the technology can be difficult to retrofit into existing structures. However, the physical aspects of a DWHR installation are relatively simple and easy to understand.

DWHR installations rely on vertically installed ‘falling film heat exchangers’. As hot drain water falls through a vertical pipe and imparts its heat to the pipe, the falling film heat exchanger — consisting of a coiled wrap of coldwater tubing that ascends around that vertical pipe — accepts that heat and carries it back for use in now-warmed water. To suit the full range of likely applications, DWHR systems are manufactured in a variety of pipe diameters, lengths, tubing diameters and water pressures.

The annual total energy savings achieved by DWHR systems for average single-family homes has been estimated at from 5% to 7% or more, depending on home design and DWHR type and installation configuration. The return on investment of such a system may range from 10% to 50%, depending on the home’s water heating fuel type and home occupancy. For large-scale multifamily or lodging facilities, and for commercial facilities, annual total energy savings may reach or exceed 9%, and return on investment will typically exceed 20%.  


This website uses cookies

As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

Show Details
HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
LoginThis is necessary to sign in to the HubPages Service.
Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
AkismetThis is used to detect comment spam. (Privacy Policy)
HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
MavenThis supports the Maven widget and search functionality. (Privacy Policy)
Google AdSenseThis is an ad network. (Privacy Policy)
Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
Index ExchangeThis is an ad network. (Privacy Policy)
SovrnThis is an ad network. (Privacy Policy)
Facebook AdsThis is an ad network. (Privacy Policy)
Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
AppNexusThis is an ad network. (Privacy Policy)
OpenxThis is an ad network. (Privacy Policy)
Rubicon ProjectThis is an ad network. (Privacy Policy)
TripleLiftThis is an ad network. (Privacy Policy)
Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
ClickscoThis is a data management platform studying reader behavior (Privacy Policy)