For the perfect hot water system, go thermal store...
From £1,350 - installed
Types of water heaters...
Conventional cylinders (hot water tanks) are vented cylinders. However, they only
provide hot water under gravity pressure. For a much better hot water system, mains-pressure
water is now provided in virtually all new homes. There are two competing systems
(apart from combi boilers). These are...
Unvented heat bank and vented Thermal Store
Both have advantages and disadvantages, and they work differently...
This is an unvented heat bank. The one on the right is a electrically-heated version.
The one on the left is heated by a boiler. An unvented heat bank is popular with
installers as it is relatively cheap to purchase. However, due to safety implications,
it must be installed and serviced by a ‘G3’ accredited engineer. An unvented heat
bank ‘banks’ the heated water for later use. As the name suggests, it is not vented
and thus is pressurised. It therefore requires a pressure release valve - and is
part of the reason why it must be serviced annually by a G3 accredited engineer.
This can make the cylinder a bit more expensive to own. Also, when an unvented heat
bank suffers from limescale, it doesn’t show until it’s far too late to do anything
about it. The cylinder has therefore come to the end of its life. This can happen
in as little as 10 years. With a replacement cost of £1,500 it would mean an annual
cost of £150 to be added to servicing and maintenance!
This is a simplified drawing of a vented thermal store. It is slightly more expensive
to purchase compared to an unvented heat bank, and is thus not as appealing to installers
(quotations for install costs would be higher). However, it requires no annual servicing.
A vented thermal store is not pressurised, and is usually fed with water from a storage
tank that sits on top. This merely keeps the cylinder full of water which heats up
and acts as a store of heat (‘thermal store’). When a tap is turned on, the water
passes through the coil and picks up heat as it traverses the coil. It requires no
pressure release valve, but it does need a thermostatic mixer valve to function.
When a thermal store suffers from limescale, flow is restricted through the coil.
This is evident, and the coil can easily be descaled for around 1/6th of the cost
of replacing it. Thermal stores 30 years old are fairly common.
We ONLY recommend vented thermal stores.
Their advantages over an unvented heat bank outweigh a cheaper install cost, as long-term
they are a cheaper way to provide hot water.