Advice needed for best boiler system

19 Jan 2013
Reaction score
United Kingdom
I want to run 2 showers simultaneously.
1 in a main bathroom and 1 in en-suite.
I am in a 2nd floor flat.
I don’t know what pressure my mains is – I have filled a 10l bucket a few times and seem to have 16l/m flow.
Flat is one level top floor so I have plenty of loft space… not much room in the flat.

What is best option for me?

Am I right thinking the incoming mains pressure and flow affects ability to run 2 showers at the same time with both a combi (even a kick-ass one) and an unvented system … but does not matter with a vented system?
With a combi you’re heating the mains water as it comes in and not storing any HW.. so the mains pressure and flow is basically ‘shared’ among all the outlets.

With an unvented system although you are storing a cylinder of HW you can still only draw off that HW at mains pressure and flow.. ‘sharing’ it between the outlets.

Whereas a vented system with a HW cylinder you can pump it off giving plenty of pressure & flow into the 2 showers … at least until the cylinder is empty? Ie incoming mains pressure and flow don’t affect the pressure & flow to the showers as this is decided by the piping and pump between the cylinder and shower head?

Is that correct … or not ???
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