Combi boiler size

[DB4193]

I'm replacing a back boiler with a combi boiler for a work project (i'm an apprentice) and I have calculated the radiator output from using their sizes and checking them against boilers on Vaillant Boiler Worcester Bosch Boilers Plumbing Supplies Heating Plumbing Radiators Henrad Quinn Boilers Baxi Boiler Vaillant Worcester Bosch Hot Water Cylinders & Copper Cylinders from TDL - Trade Distribution Ltd, with all 6 adding up to 8.27kW. Its a bungalow house so i knew the figure would be a bit lower but i was just wondering if their was anything else i need to take into account like how systems req 3kW for hot water. I have just came into the combi boiler module so dont know all the logistics.
Thanks anyone who can help.

 

[kirkgas]

the 3kw allowance for hot water comes from a system boiler with a cylinder, a combi has no allowance for hot water as it runs on full HI when the tap is open, choosing a combi size is purely down to required flow and temp of hot water, check the MI's to see what flow and temp rise they give you, a min without a shadow of doubt should be a 28kw min, unless it is a one bed flat with an electric shower and cold fill washing machine, and even then the price diff between 24 & 28 hardly make it worth buying the 24, are you sure your rads only add up to 8.27kw seems low for 6 rads? the only thing to consider is flue position, does it need a plume kit can you get the condensate connected internally, what is the gas run like to ensure you get your max HI, how come you are doing a work project as an apprentice, hope you arent getting help with a wee homer here haha