Internal services

8.1

8.1.5Hot water service

Hot water service shall be provided in accordance with statutory requirements and be adequate for the demand and consumption.

Hot water services should be designed in accordance with Table 3, and:

the minimum flow rate should be in accordance with the statutory requirements and generally be available; it may be less where the pressure and flow rate of the incoming supply falls below 1.5 bar

have the design flow rate available at each outlet when the total demand does not exceed 0.3L/s (where simultaneous discharge occurs, the flow rate at individual outlets should not be less than the minimum rate).

Table 3: Flow rate and temperature requirements

Outlet	Design flow rate L/s	Minimum flow rate L/s	Supply temperature °C
Bath (from storage)	0.3	0.2	60
Bath (from combi)	0.2	0.15	40
Shower (excluding instantaneous electric showers)	0.2	0.1	40
Wash basin	0.15	0.1	40
Sink	0.2	0.1	60

Hot water storage should comply with the minimum capacity in Table 4 (based on a draw-off temperature of 60°C), and where appliances require greater volumes, the capacity should be increased accordingly.

Table 4: Minimum storage requirements

Shower only	Bath only	Bath and shower(s)(1)	Two baths
60L	120L	145L	180L

Notes

1 Maximum of two showers (excludes instantaneous electric showers).

Where systems are heated by off-peak electricity, the storage capacity should be in accordance with the recommendations of the electricity supplier.

Where homes have one bathroom or shower room, the system should be able to provide adequate hot water:

immediately after the bath has been filled, for tasks such as washing

for a second bath after 20 minutes.

Instantaneous systems (using combination boilers) produce hot water on demand (generally at lower flow rates than storage systems), and should only be used where:

simultaneous demand for hot water is limited. Where there are three or more outlets, the design for simultaneous discharge can omit the outlet at the kitchen sink

storage combination boilers have the capacity as required in Table 4.

Where homes have two or more bathrooms, the system should be able to provide adequate hot water immediately after each of the baths have been filled, for tasks such as washing.
Where a shower is installed, adequate provision should be made to ensure that the outlet temperature of the water is not significantly affected by the use of other hot or cold outlets in the home. This may be achieved by the provision of a thermostatic shower mixing valve, the appropriate design of pipe sizes or dedicated supplies.

Where boilers can control and prioritise hot water outputs:

storage capacities can be less than the figures in Table 4

the storage capacity should be in accordance with the manufacturer’s recommendations.

Storage systems provide higher flow rates than instantaneous systems, and:

require a suitable space for the siting of the storage vessel

where vented, should be provided with an expansion pipe.

Unvented hot water storage systems should be:

assessed in accordance with Technical Requirement R3, or meet the requirements of BS 7206 and be the subject of third-party certification, e.g. Kitemarking (applies to both the assembled system and components)

installed by competent installers.

Hot water cylinders should be:

supported in accordance with manufacturer’s recommendations

installed vertically, unless designed otherwise

accessible for maintenance

insulated as specified in the design.

Where an immersion heater is fitted, it should be:

appropriate for the type of water supplied to the home

controlled by a thermostat

located to facilitate replacement

fitted with an on/off switch.