Thermo Mixer Shower - Expected Pressure/Flow Rate

Hi, this is my first post and I am a complete novice when it comes to DIY. I have recently decided to fit a Thermo Mixer Shower (Mira Excel) over my existing bath. I am wanting to know the approximate pressure and flow rate (if possible) I could hope to achieve on my current system (just a standalone system, no pump), if this is an impossible question to answer then please forgive me. My current system is as below.

I have a gravity fed system. The cold water tank is in the loft on a wooden platform, more or less directly above the hot water tank that is situated in the airing cupboard below. The difference between the bottom of the cold water tank and the position in which the shower head would be is approximately 2.5 metres.

I would estimate that 7/8 metres of pipe would have to be laid to reach the location that shower would be placed in, this does not include the 2.5 metres head difference mentioned above. If it is of any use the bath currently flows at about 20 litres a minute.

Thanks in advance for any information given, I don't expect an exact pressure/flow rate figure, just a min and/or max figure will do.

I can't tell you a flowrate but we have got a very similar set-up (with an older model Mira Excel and about the same head of water, both hot and cold through 22mm pipes) and it's, well, okay. Not brilliant but not really duff either. About the same as we used to get out of a 8kW electric shower on mains cold water.

HI

it would be 0.25 bar pressure and about 5-6 litre per minute flow rate.
this is not an accurate or exact as it might vary from pipe sizes,etc.