What Is a Waste Water Heat Recovery System?

A WWHRS (Waste Water Heat Recovery System) captures heat from warm wastewater—typically from showers, baths, or sinks—and uses it to preheat the incoming cold mains water. This process reduces the energy needed by the water heating system, improving the property’s overall energy performance and reducing carbon emissions.

The system works through a heat exchanger, which transfers heat from the outgoing drain water to the incoming cold water without the two ever mixing. 

By recovering this otherwise wasted energy, WWHRS can make a noticeable contribution to reducing domestic hot water energy demand.

• Operation: These systems recover heat in real time while the wastewater is flowing — typically during a shower.

• How it works: Warm wastewater passes through a vertical heat exchanger (often a copper coil or double-walled pipe). As the waste water drains, it transfers heat directly to the cold mains water feeding the shower or hot water cylinder.

• Advantages:

• Simple design, no storage tank required.

• Minimal maintenance.




• Very efficient during continuous flow (e.g. showers).

• Limitations:

  • Only works when hot water use and wastewater flow occur simultaneously (e.g. during showering).

  • Less effective for baths or sinks where water is drained after use.

• Operation: These systems store recovered heat from wastewater in a thermal storage unit before it’s reused.

• How it works: Wastewater heat is captured and transferred to a storage tank containing clean water, which then preheats the cold mains water feeding the main water heater.

• Advantages:




• Can recover heat from any source (showers, baths, washing machines, etc.).

• Works even when wastewater and cold-water demand don’t occur simultaneously.

• Limitations:

  • More complex and expensive to install.

  • Requires space for a storage vessel.

  • May have some standby heat losses.

For Heat Recovery Systems we have the ability to select the type of system as:

• Instantaneous or
• Storage

If instantaneous is selected, we have the option to enter up to 2 system, the search the PCDF for the system at the property.

If Storage is the chosen option, then we have the ability to enter the WWHRS Store Volume, and search the PCDF for the system.

Below you can find a range of systems that appear when searching the PCDF. Select the correct system using the radio button on the left, and clicking the 'Select' button. This will add the correct system to your assessment.

So, if you come across WWHRS at a property you should now understand how you are able to input this Heat Recovery System into the software.