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GreenFoX™ Drain Water Heat Recovery (GFX DWHR)

Capture the heat going down the drain and use it to preheat incoming cold water.  Replace a vertical section of the drainpipe; it needs only gravity and running water for year round operation and continuous savings.

Drain water heat recovery devices improve efficiency by warming incoming cold water with heat absorbed from draining warm water. 

DWHR systems do not replace existing hot water heating systems, but rather enhance them by reducing their workload and increasing their performance by preheating the incoming supply water entering the hot water heating system.  Whether a using tank, tankless, solar, and geothermal or any other type, the preheated water coming into the heating system will reduce the amount of energy required to bring it up to the operating set point of the system.

Read more about The Other Side of Drain Water Heat Recovery in the Radiant & Hydronics Report July 2017

After a quick, four-connection installation into a vertical section of the main drain line, it goes to work.  That is all it does, for 30+ years, it takes the heat out of hot water and sends it right back to heat more.  There are no moving parts to break or service, no seasonal maintenance to worry over, no adjustments to make.  Soon it becomes the norm for the utility bill to be lower, for the water heater to work less, and for there to be what seems like a never-ending supply of hot water; so no one has to race to be the first one in the shower.

The average payback on a DWHR system is about 2 -7 years, depending on how often the system is used (ie: how many people in your household taking showers), the type of heating fuel used (gas, electric, or other) and the installation type.

Because of its all copper design it will last the lifetime of your plumbing, up to 30 years! So even after you recapture your initial monetary investment it continues to work for you by saving money, prolonging the life of your water heating system and all the environmental benefits. Not to mention making your hot water last much longer and that sudden cold shower a thing of the past!

Our coil and tube heat exchangers use Gravity Film eXchange Technology. As water goes down a vertical section of a drain pipe, it naturally clings to the inner surface of the pipe in a very thin film. The heat from this film is transferred to the incoming fresh cold water circulating up through the coils around the outside of the heat exchanger (which is now a part of your drain pipe). The incoming cold water is preheated before it goes into the water heater - it is in that way you are saving money and energy while increasing hot water capacity.


The heat exchanger becomes part of your drainage stack, usually in your basement, by replacing a vertical section of the drain line.  The coils become part of your fresh water supply line by diverting it through them. It can be installed with any combination of drainage pipe and fresh water piping (i.e.  ABS, PVC, cast iron, copper, PEX, etc).  Only 4 plumbing connections are needed -- 2 for the coil and 2 for the drain (using no-hub connectors).

Sizing & Placement

Because longer units have more surface area they are able to transfer and recover more heat energy.  The same is true as the drain diameter of the unit increases from 3" to 4". Larger units with greater surface area recover the most heat and deliver greater energy savings.

A) Determine size of drain (2”, 3” or 4” is normal)

B) Find longest section of available vertical space in your main drain line (30” to 60” is common)

C) Cold water supply connections ¾” (??)

For larger residences and commercial uses, units can be connected in series and/or parallel.  36” units are great for limited clearance and crawl spaces (custom sizes available on request).

Units can be installed on the second floor, first floor, crawl space and basement – virtually anywhere there is access to a sufficiently tall section of VERTICAL waste pipe having waste hot water flowing through it, along with access to a cold water supply line. The heat exchanger may be installed in more than one location, as on-site conditions may allow. For best results, install as close to the exit of the main drain line as possible.

For maximum savings, use the Equal Flow configuration - plumb the pre-heated water from the unit to both the water heater and the cold line, feeding all plumbing fixtures. Preheating the cold water to fixtures like a shower significantly reduces the amount of hot water needed. This also creates an equal flow where the total preheated water being used is equal to the total water going down the drain.   


Since the heat exchangers diameter is the same as the existing drain, there is no clogging or build up created. A completely passive system with no moving parts means there is no maintenance, ensuring long lasting operation for peak efficiency and ease of mind!     

Code compliance

Certified by independent organizations as a double-wall-vented heat exchanger approved for potable water use according to the Safe Drinking Water Act, safety tested and constructed in accordance with federal, state, and local plumbing codes.

  • Intertek ETL/Warnock Hersey mark
  • IAPMO PS 92      Standards for Heat Exchangers
  • IAPMO 2012 Green Plumbing and Mechanical Supplement Code Section 606.0
  • CSA B55.1 DWHR Performance Standard
  • CSA B55.2 DWHR Safety Standard