How to buy a hot-water cylinder

If your home’s central heating system is in need of an update, a new hot-water cylinder will help. Geoff Egginton from the Hot Water Association has some expert advice.

1. Being able to supply multiple outlets (taps, baths, showers, etc) is one of the main benefits of a cylinder-based hot-water system, making cylinders perfectly suited to homes with more than one bathroom.

If another member of your household uses a different shower or bath at the same time as you, a cylinder can supply hot water to both without significant loss of pressure or an adverse effect on the temperature.

2. Today’s cylinders are highly insulated and efficient, and are available in a variety of sizes to suit your household – your installer should be able to advise you on the right size.

If you’re replacing an existing cylinder and have added to your household’s hot-water needs, perhaps by expanding your family or adding outlets, you may need a cylinder with a larger capacity.

The new cylinder will usually be taller than the old one and may have a larger diameter to meet current insulation requirements, but it won’t need a separate insulation jacket.

There is often no need to replace the boiler at the same time, unless it’s old and inefficient.

Only system and regular boilers work with cylinders, so if you have a combi boiler and want a cylinder, the boiler will have to be changed.

Cylinders usually have an immersion heater, which can be used to heat water if the boiler’s turned off or out of action.

3. Choose from a vented/open-vented cylinder (with a regular boiler), where water for the cylinder is drawn from a cold-water tank, or an unvented cylinder (with a system boiler), where the system is sealed and water is drawn at mains pressure.

If you have a vented heating system, changing to an unvented system will do away with the need for water tanks and the worry associated with open water storage. It may also increase the water pressure.

4. When deciding which cylinder to buy, look at the heat-loss figure (how long the cylinder takes to cool down), the reheat time (how long the cylinder takes to reheat after hot water is drawn off) and the insulation thickness.

These figures should be supplied by the manufacturer and so shouldn’t be difficult to find and compare – you may find that spending a bit more on a cylinder will give you greater savings in the longer term.

Cylinders are now supplied with an energy-efficiency label that provides a rating for the cylinder.

5. If you have solar thermal (water-heating) panels or are thinking of installing them, go for a cylinder with two heat exchanger coilers (twin coil).

One coil is connected to a boiler (or heat pump) and the other can be connected to solar thermal panels to store any solar gain collected during the day.

If you don’t have or want solar thermal panels, a single-coil cylinder is fine – this is designed to be connected to just one heat source, usually a boiler.