What seems like a basic hot water system in many countries around the world is finally catching up in the UK. Unvented hot water cylinders and central heating systems provide hot water at mains pressure level. Unvented systems eliminate cases where two users cannot draw hot water simultaneously, for example when one member of the household having a shower while another tries to do the washing up. Unvented systems use the pressure of the mains infrastructure to retain sufficient pressure of hot water around the entire house. This is in stark contrast to the traditional gravity fed systems with a feeder tank normally positioned in the loft, offering low pressure in the top floors, due to lack of head for the hot water to build up pressure.

In recent decades, typical dwelling designs have evolved remarkably. Many households now have two bathrooms, and many others have a whirlpool bath, multi jet shower or other appliances that use hot water. More so, our hectic lifestyle means we want hot water on demand, without having to wait for it, or having to accept a trickle in the shower. A correctly sized and designed system around an unvented cylinder can provide the perfect solution for all those demands, offering a reliable availability of hot water any time of the day in a sufficient pressure for domestic needs, be it the hot water shower, or the kitchen tap.

Unvented cylinders are made of metals that can be broadly grouped into the following three groups: copper, stainless steel and sheet metal. All three are reliable and used around the world. They naturally differ and have unique advantages and disadvantages.

* Copper tanks - their price has rocketed in recent years following the commodity's sharp price rises. Copper tanks are relatively light and easy to maneuver into the house. However, they are less effective at heat retention and suffer from heat loss unless covered with a very thick insulation.

* Stainless Steel tanks - the most expensive of the three, offering longer lifetime, but at a price. They have good heat retention, and only a little heavier than copper tanks.

* Sheet metal shell - offers the best heat retention properties, and is cheapest of the three technologies. Although heaviest of the three, sheet metal shells are highly popular in the rest of Europe and normally come with an inner enamel glazing, thus reducing build up of scale.

There are several important parameters to remember when choosing your unvented hot water cylinder:

* Volume and external dimensions - a typical household (4-5 people) in the UK will require a 200 liter cylinder. However, the cylinders come in different shapes and dimensions. Make sure to check the width and height of the cylinder, so that it fits in the airing cupboard (or any other space you plan to position the tank in).

* Heat retention performance - since the main purpose of a hot water tank is to retain the water inside hot, it is important to check the heat loss score of the tank. A good tank loses less than 3 kW per 24 hours).

* Manufacturers' warranty and support - unvented cylinders are simple systems, with no moving parts. This makes them reliable over many years. However, it is important to check which warranty and service support is offered by the manufacturer.