Types of hot water systems

There are two basic types of water heater - storage systems and instantaneous (or continuous flow) systems.

Storage water heaters 

Water is heated and stored in an insulated tank for use when it is required. These systems can operate on mains pressure or from a gravity feed tank.

Mains pressure

Hot water is delivered at a similar pressure and flow rate to cold water, so more than one outlet can usually be turned on without affecting pressure. The storage tank is usually located at ground level inside or outside the house.

Constant pressure or gravity feed

Hot water is delivered at lower than mains pressure from a tank located in the roof of the house. Pressure depends on the height difference between the tank and the point of use.

Gravity feed systems are most common for properties not connected to mains water. Storage tanks may be made of copper, glass (enamel) lined steel, or stainless steel. Copper and glass-lined tanks typically have a sacrificial anode to reduce tank corrosion, which needs to be replaced every five years or so, depending on water quality. Warranties offered for tanks range from 5 to 10 years, and details vary considerably. We recommend that the anode be replaced every three years.

Instantaneous water heaters

Instantaneous systems heat only the water required and do not use a storage tank. They can operate on natural gas, LPG, or electricity. Gas models are available with either electronic ignition or a pilot flame or hydro-powered units.

Instantaneous systems cannot run out of hot water and can be mounted internally or externally.

Standard units can only deliver adequate hot water to one or two points at the same time, but high-performance gas units can supply several points at once. They also have sophisticated temperature controls.