Domestic Hot Water (DHW)

Select the most efficient means of generating hot water (DHW)

• electric point of use hot water heaters in rooms requiring small quantities of hot water (3)
• gas point of use hot water heaters in areas requiring larger quantities of hot water (3)
• hot water storage cylinders [with plate heat exchangers] (3)

Minimise heat losses from hot water (DHW) boilers, pipework and storage

• isolation on the pipework between calorifier and boiler to prevent wasteful heating, where electric immersion heaters are use to provide summer hot water and the boiler is switched off (3)
• reducing the number of hot water cylinders and/or the volume of hot water storage if possible [unnecessary storage] (3)
• insulation on all hot water storage cylinders (3)
• insulation on all hot water distribution pipework (3)
• hot water pipes above cold water pipes to reduce heat transfer (5 - FactSheet 11)

Provide effective hot water (DHW) controls

• immersion heater thermostat at 60degC (3)
• timeswitches to provide one or two separate 2-hour heating periods during the day (3)
• immersion heater timeswitches to switch off about an hour before the end of daily occupancy to make best use of stored hot water (3)
• a system of using off-peak electricity for water heating and install an off-peak controller with daytime top-up facility if appropriate (3)
• an electronic timeswitch to all immersion heaters (3)

Avoid heat losses

• insulate hot water distribution system pipework and storage tanks (2 - measure DS8.2)

Avoid excess water storage

• instantaneous and semi instantaneous domestic hot water heaters to reduce standing losses where demand is highly diffuse and sporadic (2 - section D5)

Reference Documents

	Series Number	Publisher	Title
1	GN 12/97	BSRIA	Oversized heating plant - a guide to reduce the energy consumption of oversized water or steam heating and DHW plant
2	COP 6/99	BSRIA	Environmental Code of Practice for Buildings and their Services
3		Carbon Trust	Focus - the manager's guide to reducing energy bills
4	Guide F	CIBSE	Energy efficiency in buildings
5	WFS11	EA	Plumbing and heating system design and management