New SAP Feature: Electric Showers and WWHRS

A new feature has been unlocked in SAP! 🥳

We can now attach Waste Water Heat Recovery systems to electric showers.

The shower has to be an approved Modulating Instantaneous Electric Shower (MIES, for those who love a new initialism) which, so far, is limited to the Mira Heatloop.

I’m reliably informed other manufacturers will have approved listings available very soon.

Pic Mira. Heatloop WWHRS with a modulating electric instantaneous shower.

❓ Why is this a new thing in SAP?

Until now, SAP has only let us pair a WWHRS system with a mixer shower (fed from the dwelling’s hot water source).

🚿 Mixer showers have built-in thermostats, so when the WWHRS is pre-heating the incoming water supply, the mixer shower notices a rise in water temperature, reduces the flow rate of hot, increases the flow rate of cold, and keeps the shower temperature consistently comfortable.

But older, more basic electric showers don’t offer the same control.

It's either heating the water with its collection of kettle elements at full power, or it’s not heating at all.

The concern with pairing WWHRS and basic electric showers together, is that the combination of full power from the shower plus the added heat from the WWHRS recovery could increase the water temp to something resembling lava. 🌋

A modulating electric shower turns down the power if the water is hot enough.

Throw a WWHRS into the mix, and the shower gives you comfortably hot water while using less electricity.

The new feature, available through the Special Features / Appendix Q section of SAP, gives a reasonable reduction to the hot water electricity demand (actual results will vary depending on dwelling design and spec).

It’s available in the current SAP10.2, the Future Homes Standard SAP10.3, and rdSAP10 for existing building surveys.

❓ Is this the answer to all my Part L problems?

This new feature can be used to improve results for dwellings with electric showers.

Also, it should improve EPCs by a couple of points in retrofit projects.

But for new dwellings being designed to the Future Homes Standard, with mixer showers, heat pumps, and mandatory PV, they should tick all the compliance boxes without needing additional tech. ✅

Still, it’s a useful option where installing mixer showers is challenging, or where the developer is looking to exceed Part L / EPC targets.

If you’ve got a house design with electric showers, and needs a nudge in the right direction of a compliant calculation, ask your friendly neighbourhood SAP assessor to have a look.