Hot Water And Scald Protection

Hot water in any dwelling has to satisfy two requirements that conflict.

Stored hot, so bacteria cannot multiply in the cylinder. Delivered cooler, so it cannot scald somebody at a basin or a shower. The device that resolves it is a tempering valve, and in supported accommodation it is a safety item rather than a fitting.

Why it matters more here

A resident may have reduced sensation and not feel that water is dangerously hot. They may be unable to move out of the water quickly. They may be assisted by somebody else who is controlling the tap.

Which raises the consequence of a valve that has drifted, and makes the maximum delivery temperature a design decision rather than a default setting.

The bathroom that it serves is designed around the same considerations, set out in [accessible bathroom design in SDA](/blog/accessible-bathroom-design-in-sda).

The valve is a maintenance item

Tempering and thermostatic mixing valves have a specified service interval and a cartridge that is replaced rather than cleaned.

They fail by drifting, by seizing, and occasionally toward hot. Which means the valve is positioned where it can be reached and serviced without opening a finished wall, and it is included in the maintenance schedule from handover rather than discovered years later.

Accessible placement is a design decision in a factory build, because a valve buried behind a lining is a valve that will not be serviced. That sits with the rest of [services coordination in modular delivery](/blog/services-coordination-in-modular-delivery), and it carries into [maintenance and whole of life costs](/blog/maintenance-and-whole-of-life-costs).

Capacity, not just temperature

A dwelling with several residents, assisted showering and a laundry running has a hot water demand profile that is nothing like a family home.

Which means the system is sized on the actual pattern: how many showers, how close together, how long each one takes with assistance, and what else draws at the same time. An undersized system produces cold water mid shower, which in assisted showering is a genuine problem rather than an inconvenience.

Recovery rate matters as much as storage volume. A system that empties and takes two hours to recover does not suit a morning routine with four residents in it.

The dead leg problem

A long run of pipe between the valve and the outlet holds cool water that has to be run off before hot arrives.

Which wastes water, wastes time, and in a dwelling where somebody is waiting undressed it is a comfort issue. The fix is layout: fixtures grouped so the runs are short, or a circulation arrangement where they cannot be.

In a factory build the pipe routes are set when the modules are built, so the layout decision has to be right in design rather than adjusted on site.

All electric and heat pumps

An all electric dwelling with solar uses a heat pump or an electric storage system, which changes the recovery profile and the placement.

Heat pumps need air flow and they make noise, which means the position is chosen with the neighbour and the bedroom window in mind rather than with the shortest pipe run. The rest of that system logic is in [solar, batteries and all-electric dwellings](/blog/solar-batteries-and-all-electric-dwellings).

What goes in the handover record

The system type and capacity, the valve type and its service interval, the set delivery temperature, and the measured temperature at each outlet at handover.

The last one is the useful part. A measured baseline means the next service can tell whether the valve has drifted, and it proves the obligation was met at handover. That record belongs in [handover documentation and as-built records](/blog/handover-documentation-and-as-built-records).

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