I am building an en suite bathroom (incl shower) to a ground floor bedroom. The cold water tank is in the roof (above first floor), the hot water tank & boiler are on the first floor. The system is a conventional system. The horizontal distance from HWS tank/CWS tanks to the proposed shower is 13m horizontally and approx 3.4m vertically. I have been in houses where the hot water cools down in transit in the pipes and it takes ages to get the water hot in the shower. So are the distances above too long for an efficient shower? I am concerned with water wastage & water temperature here.
Certainly a shower will physically work simply because of the head of water available. It may even be possible to use a 15mm flow as that would reduce the amount of cold draw off required before the hot reached the shower and heavy insulation would remove the possibility of a fall in the supply temperature whilst the shower is in use, but for the inevitable waste of the first flow of cold water is down to your decision.
Personally, I have installed flows to this distance without a second thought. If you want a shower.........
if the pipes are accessible you could lag them. foam lagging is available anywhere. i recently completely replumbed my house and lagged all hot pipes everywhere, F&Rs on the heating and the domestic supply.
even just lagging the accessible areas of the hot feeds will be a help.