Unvented water heaters are one of two types of water heater used in residential applications. The key difference between an unvented water heater and a vented heater is that unvented boilers are sealed. Therefore this particular system is dependent on the installation of an expansion vessel.
As water is heated, the pressure can increase by up to 4.5%. An expansion tank allows for this increased pressure which means it is a vital part of any sealed system. The boiler expansion vessel contains a certain amount of air within it; this absorbs excess water pressure caused by thermal expansion.
The unvented water heater is cost effective and is ideal for small or medium sized businesses due to the flexibility of installation. The water heater produces mains pressure hot water and a balanced supply of output to each outlet it supplies. This therefore means they can be used to power multi-basin installations effectively. There is also no need for a separate cold water cistern which results in a more flexible installation process.
Each manufacturer produces heaters designed to operate reliably under the increased pressure produced by high temperatures. Unvented water heaters are also fitted with a thermal cut-out device which provides a maximum water temperature to prevent dangerous increases in pressure.