What is an unvented hot water system?

An unvented hot water system has no cold water feed tank but rather has a sealed (unvented) hot water cylinder fed directly from the cold water mains, and uses mains pressure. The unvented cylinder maintains a pressure from an incoming water supply.
Unvented systems are ‘sealed/closed’ systems and so require additional equipment, such as an expansion
vessel to manage the changes in pressure within the system as the water within heats up.

Direct fired water heaters installed in an unvented system at an Aademy

What are the benefits of an unvented system?

Because the unvented hot water system does not require a separate cold water feed tank - and the associated pipework linking the tank to the cylinder – it takes up less room. In a large commercial system, this also means they are simpler and quicker to install.

The water pressure tends to be better with an unvented system as the pressure comes from the mains feed. This means that with an unvented system outlet pressure is better and, therefore, taps and showers perform better. Unvented systems also do not run the risk of freezing in the winter and are less prone to contamination.

What is an unvented kit?

Unvented hot water systems require specific components to ensure they run safely and efficiently and meet the legal safety requirements laid out in Building Regulations Approved Document G, section 3. An unvented kit will often contain these components including an appropriately sized expansion vessel, valves and fittings.

What unvented kits are available from Hamworthy?

We can provide unvented kits for all our water heater products – calorifiers and direct fired water heaters. These differ slightly depending on the product range, but generally include:

  • Strainer
  • Pressure control valve
  • Balanced cold supply connection
  • Non-return valve
  • Expansion relief valve
  • Expansion vessel connection
  • Expansion vessel appropriately sized
  • Temperature pressure relief valve
  • Tundish

The components can be supplied as separate items or as a combined group.

The new unvented kit now available with our Dorchester water heaters comes with a combined inlet control valve saving you time and money.

Please refer to the product brochures for more information on unvented kits.