Head for combination cylinder?

[drivewasher]

Long story- short version,
Industrial unit and offices I do some work for have a failed 10kw instant water heater to serve brew room sink, male + female wash rooms, 3 hot taps in all. Heater is in a crawl space behind ladies wash room is apain to get to have to unscrew decor panels.
They want me to fit a hot water vented cylinder and immersion heater and build an airing type cupoard around it in the large-ish ladies washroom, the question I have is as the ceiling is about 7 foot high and the taps are all standard worktop height about 3 foot. This will give a head from top of cold feed tank (built into a combination cylinder) to tap outlet realistically about 3 foot allowing for access in top of feed tank for maintenance etc;
If I use 22mm copper from outlet on cylinder to as near to the taps as poss useing a reducing coupler to 15mm as taps are 1/2 inch will this give enough flow for handwashing and small kitchen sink for cup washing etc;
Also can the overflow be connected into the inch and half plastic waste pipe that runs where the cylinder would be useing a tundish & trap arrangement

 

[pierrot]

why dont you fit an unvented cylinder with an immersion, get the best of both worlds then.

 

[chrishutt]

For a relatively light application like that you could use a 15 litre unvented water heater. These small 3 kW storage units can be installed by any competent person (unlike the larger unvented cylinders) and will give mains pressure hot water and cost about £120 each. The only significant problem with these might be accommodating the Pressure Release Valve pipe, which should discharge to outside.