How WWHR works
A waste water heat recovery unit is typically a vertical copper heat exchanger plumbed into the shower waste. Warm grey water spirals down the inside surface while incoming cold mains water passes around it, pre-warming the cold feed to the shower mixer and/or cylinder by recovering around 40–60% of the heat that would otherwise go down the drain.
No moving parts, no electricity, no maintenance — it just sits in the pipework. Vertical units (through a floor) perform best; horizontal variants exist for ground-floor showers.
Why SAP 10 made it standard
The SAP 10 notional dwelling assumes WWHR on all showers — so a dwelling without it starts behind target. For the modest cost of a unit per shower, WWHR is among the cheapest CO₂ and energy savings available in a SAP calculation, particularly in homes where showers dominate hot water use.
It also helps Part G water-energy crossover thinking: shower flow rates now feed both calculations, so fittings choices pay off twice.
Specify it at design stage — retrofitting into finished pipework is far harder. Ask us where it earns most in your SAP.