Page 374 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

Hot water storage cylinders must conform to BS 1566, which specifies the
minimum heating surface area of the heat exchanger.
● Existing double feed indirect systems: existing double feed indirect systems
use gravity circulation via 28 mm gravity primary flow and return pipes to
heat the water in the cylinder. This type of system can no longer be installed
as they are extremely wasteful in terms of energy usage. Document L1B of
the Building Regulations recommends that these systems should be replaced
with fully pumped systems wherever possible (see Chapter 7, Central heating
systems) or they must be updated to include a cylinder thermostat and
a motorised zone valve arrangement, as stated in the Domestic Heating
Compliance Guide. This is to limit the amount of energy wastage.

22 mm vent from primary hot water system connected to the boiler,
the coil in the hot water cylinder and central heating system
22 mm vent from secondary hot water system. To determine the height
of the vent = 150 mm + 40 mm per metre of system height (m)
Feed and expansion cistern
fitted with BS1212 part 2
150 litre storage cistern fitted with BS1212 part 2 float-operated valve float-operated valve
Spherical ball-type
service valve
Spherical ball-type
service valve

15 mm cold feed to
22 mm or 28 mm cold feed to the primary system
secondary hot water system
22 mm or 28 mm full-way
gate valve or lever-type
spherical ball valve
22 mm draw-off to the bath then
reduced to 15 mm to all other services 450 mm

22 mm primary flow and
return pipes from the boiler
to the coil in the cylinder
Heat source. Gas, oil
or solid fuel

p Figure 6.5 Indirect open vented (double feed type) hot water storage system

● New double feed indirect systems: on new installations, double feed
indirect cylinders must incorporate pumped circulation to the heat
exchanger. Document L1A of the Building Regulations dictates that all
new installations must have pumped primary circulation with controls
that prohibit energy wastage. This is achieved by installing thermostatic

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