Instantaneous hot water or hot water storage?




Instantaneous or hot water storage?

The first consideration and decision to make is whether the needs of you, your family, or visitors will be met by an instantaneous or a stored hot water system.


Instantaneous water heaters

		Heat water on demand, and vary from the small hand wash units often seen in public buildings, to electric showers or combination boilers. Combination boilers are so called because they combine the traditional capabilities of a standard central heating boiler with the added functionality of being able to utilize the full boiler capacity to heat water instantaneously.

Advantages

Disadvantages

Heats the water that you need on demand when you need it

Where water is blended for example a combination boiler feeding a shower-mixing valve the flow rate is generally good depending on the boiler output

No stored water tanks in the dwelling

Mains water pressure means you can fit a water outlet, tap or shower almost anywhere within the dwelling

Less to install therefore greater flexibility and more space

Less risk of pipes freezing.

Major problem if the instantaneous heater breaks down (buy a reliable branded product)

Lower flow rates than stored systems, and flow rates decrease further in the winter when the incoming water supply is colder.

No airing cupboard, often a small radiator is added to compensate, at a cost if central heating is installed.

Electric units require specialist wiring, in some cases e.g. a 10 KW electric shower fresh wiring may need to be installed back to the main fuse box.



Storage water systems.

		Water is heated either directly in the storage cylinder, for example by an electric immersion heater or from a remote boiler. The two main types of system are the open vented and the un-vented. The open vented water system relies on a large volume of stored water, usually located in a plastic water tank in the attic. The weight of stored water is usually sufficient to push water down the pipe that feeds the water storage cylinder and back up to any tap or shower outlet, providing it is lower than the stored water level. The un-vented stored water system in general terms relies on mains water pressure to push the water out of the cylinder or through the pipe circuit to the tap or shower outlet

Advantages

Disadvantages

High flow rates depending on height of stored water or mains pressure

Power shower capability depending on choice of cylinder

Low maintenance costs especially with electric heating (excluding remote boiler)

Gain the traditional airing cupboard

Less risk of being without a hot water supply due to breakdown.

Regular maintenance required on un-vented units

Need to pre heat hot water to match demand

Hot water availability is restricted by the heat recovery time period and size of cylinder

Require storage tanks and space

Risk of pipes freezing in winter.





You will need to research the individual systems in more detail to be able to make an informed choice of water heating system. The links below gives a summary overview of the systems that are available.

	Open vented stored water systems
	Mains pressure hot water heating systems
	Thermal storage water cylinders
	Un-vented hot water heating systems
	Direct fired gas water heaters.

Instantaneous or hot water storage?