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Changing to unvented system.

View the thread, titled "Changing to unvented system." which is posted in UK Plumbers Forums on UK Plumbers Forums.

I have a client who wants to change from a vented to an unvented system. However it is a large house with multiple outlets as I will explain.

The main house has 3 bathrooms, one has a gravity shower, one has a gravity pumped shower and the 3rd just a bath. In a seperate part of the house there is another bathroom, it has an electric shower and a bath fed from a seperate direct vented system with its own CWST. There is also a self contained apartement with a combi boiler and another bathroom fed from that. In addition there is the kitchen and a utility room.

The main water supply is a 20mm MDPE pipe and it is distributed around the house by 15mm pipes, all cold water taps are fed from the main. The local water authority has tested the supply and say there is 4 bar pressure and delivers 27 liters per min, however this seems very high.

If the system is change to an unvented system then the cold water will supply:
The unvented cylinder
4 Basins
2 Showers
1 Bath
1 Electric shower
The CWST of the seperate bathroom which will stay the same
The combi boiler in the apartment
The Kitchen
The Utility room

A mainsboost accumulator of any size could easily be fitted, the cold supply pipework to a new unvented cylinder can easily be made in 22mm and the initial hot water distribution is already in 22mm. The supply pipework for the cold water supplies would stay in 15mm as it would be too difficult to upgrade.

I don't think an unvented would work without a mainsboost, would it work okay with a mainsboost fitted?
 
Depends what pressure your getting out of your cold mains yes they have stated 4 bar and 27 lpm but have you tested this also what is the dynamic pressure and flow ?

If you have will be fine just stick an 200-300 l accumulator on as well you will be golden
 

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