What are mains pressure hot water systems?

Installing a mains pressure hot water system may be worth considering as they usually out perform traditional system by providing higher pressure and flow rates, however a mains pressure system is only as good as the mains supply feeding it. We aim to give you all the information you need to decide if an unvented system is the right choice for you and your home.

As mentioned a mains pressure system is only as good as the supply entering the property. This means the new hot water system relies on the pressure of your existing mains supply. A mains pressure hot water system does not improve or pump the water around your home. Simply, if you have good pressure and flow from the cold taps in your property your mains pressure is suitable for a mains pressure hot water system.

In a traditional system the cold water is supplied directly from mains where as the hot water is heated stored in a tank and then fed to the hot taps by gravity, this is why the cold water usually comes out of the tap much faster than the hot water. In a property with a mains pressure hot water system both the hot and cold outlets are fed directly from the mains supply. The mains pressure hot water system includes equipment which is able to heat the water under pressure as it flows from the main supply to your hot water tap.

Choosing your system.

Heating water at pressure requires very different equipment to that of a traditional gravity fed system. A low pressure copper cylinder which is usually fed by a cistern in a loft would not be compatible with a mains pressure system and would probably explode! Combi boilers are also connected directly to the mains but the flow of water is reduced in to the boiler and they do not deliver hot water at mains pressure. A mains pressure hot water system requires a specialist cylinder that is able to heat the water safely without reducing the flow rate. 

Unvented Mains Pressure Systems

Unvented systems fill a vessel with water directly from the water main which is kept under pressure from the main supply. The water held in this vessel is then heated using immersion heaters or by heat source located outside the vessel such as a gas boiler or solar power. In an unvented mains pressure hot water system the cylinder is not vented to atmosphere in the same manner as a traditional gravity copper cylinder. The cylinder is connected by pipes to the hot water outlet. When you turn on a hot water tap the hot water is pushed out of the cylinder by the incoming cold water from the mains supply. So as the incoming cold water supply keeps the contents of the cylinder pressurised the hot water is delivered at the same pressure as the cold water supply. These cylinders are made of either stainless steel or heavy gauge copper as they have to withstand considerable internal forces.

Things to consider:

  1. Unvented hot water systems should only be installed by a qualified engineer as described in Building Regulations G3.
  2. Pressure relief valves and pipework must be installed as a precaution to prevent pressure build up.
  3. Your local authority should be advised if you are installing an unvented mains hot water system.
  4. Your system will need to be checked annually to ensure all safety equipment is functioning properly.

All of our engineers are fully accredited and G3 certified. If you have any questions or would like a quote for an unvented heating system please call us on 02380 366 423.