Drainage water heat recovery (DWHR)


DWHR devices have been well understood for over a decade, but their potential is not fully realised due to various losses. REN+HOMES will focus on different innovations to reap the full benefit of these systems, facilitating wider uptake in Europe and saving much energy.

Target technical data

% of recyclable (or reusable) product

>80% as most the product weight isthe copper of the heat exchanger



Energy savings potential

100TWh/yr if implemented in every building

State of the art and main challenges

For over a decade, drain water heat recovery (DWHR) device theory and installation have been well-established. Vertical DWHR pipes achieve considerable efficiency, leading to practical savings of around half after accounting for losses. DWHR holds significant promise for energy savings in Europe, playing a vital role in lowering DHW energy consumption. This is particularly important compared to space heating, especially in heat pump applications. Moreover, DWHR can be seamlessly integrated into renovation projects involving water system upgrades.

Innovations and added value

DWHR captures warm water’s heat to preheat fresh water for domestic hot water (DHW), focusing on showers as a significant DHW consumer. DWHR systems do this by using waste water and a heat exchanger, without added storage or moving parts. Despite their readiness and benefits, vital questions remain, necessitating field monitoring.
Three key project innovations are:

  1. demonstrating practical energy savings
  2. regularly assessing system performance in the lab to refine assumptions and evaluate models
  3. exploring DWHR viability in countries like Austria where it’s less familiar.