Waste Water Heat Recovery for Showers
SAP, Part L & HEM
Understand how WWHRS is recognised within SAP, Part L and the upcoming Home Energy Model (HEM).
As a recognised technology listed in the Products Characteristics Database (PCDB), WWHRS is fully supported within SAP (Standard Assessment Procedure) and RdSAP (Reduced Data Standard Assessment Procedure) and remains one of the most cost-effective ways to reduce hot-water energy use and improve SAP scores.
What is SAP?
SAP is the Government’s approved methodology for assessing the energy and environmental performance of new and existing homes. The latest methodology, SAP 10, underpins Part L of the Building Regulations and offers a more accurate representation of how modern homes use energy. With updated carbon factors and improved modelling for technologies such as heat pumps and Waste Water Heat Recovery (WWHRS), SAP 10 provides clearer insight into:
- Energy consumption
- Hot water demand
- CO₂ emissions
- Energy efficiency ratings (SAP score)
Appendix Q and Product Recognition
Under SAP, Appendix Q provides a route for innovative technologies to be included in modelling using verified product-specific data. Recoup’s WWHRS product ranges, including Recoup Pipe Hex, Recoup Easyfit+, Recoup Drain+ and Recoup Heatdeck™ are listed in the PCDB, ensuring their tested performance values are applied correctly in SAP calculations.
As part of the Government’s transition to HEM, the Appendix Q recognition process is being modernised, but PCDB-listed performance remains valid and in use for current SAP assessments.
WWHRS in SAP
Hot-water heating remains one of the largest energy demands in modern, well-insulated homes, which makes WWHRS one of the most effective and low-cost measures for improving SAP performance.
Within SAP, the energy savings from WWHRS are applied directly to the rooms where showers are connected to the system. The level of impact depends on several modelling factors, including SAP-calculated occupancy, the number of shower or bath-and-shower rooms in the dwelling, how many of those rooms are served by WWHRS, and whether the fixtures are shower-only or combined bath/shower setups.
The chosen installation method – System A, B or C – also influences recognised performance, as SAP models each configuration differently. When these elements are aligned, WWHRS delivers a consistently strong uplift in SAP results, helping developers and design teams meet Part L requirements more easily and cost-effectively.
The Move from SAP to HEM
The UK Government is introducing the Home Energy Model (HEM) as the next-generation replacement for SAP. HEM will become the core calculation engine used alongside the Future Homes Standard.
Key improvements include:
- 30-minute time-step modelling
- More accurate representation of hot-water and low-carbon technologies
- Better integration with heat pumps, PV and smart controls
- A modernised system replacing Appendix Q
SAP remains in use, and a transition period is expected where SAP and HEM operate in parallel. Recoup WWHRS products will be included under both methodologies.
Why Recoup Energy Solutions?
- Expertise across current SAP, Part L and upcoming HEM requirements
- Accurate performance modelling for WWHRS across residential and commercial-style projects
- Support for developers, assessors and design teams
- Guidance aligned with both current regulations and forthcoming changes under the Future Homes Standard
Whether you’re modelling new homes, reviewing specifications or preparing for the shift from SAP to HEM, Recoup WWHRS can help your project maximise efficiency and stay compliant.
Relevant Products
Pipe HEX Range
Easyfit+
Drain+ Range
HEATDECK™
SAP Support
Recoup Energy Solutions can offer support to specifiers / SAP assessors to help ensure that the impact of WWHRS is optimised for a specific dwelling. Please contact us for more information.
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