It doesn't matter how many radiators you have - it's the size of the radiators you take into consideration.
To calculate the correct size radiators you need to know each room size.
Calculate the heat requirements for the rooms, the heat that will be emitted from the radiators and the heat that the boiler will produce, taking into account heat losses from pipework and you will be able to create an cost effective heating system, that will heat the house properly.
Or ask yourself - do the radiators get hot ? heat the house/rooms ? then it's working and i'm warm.
Sorry - but it's not as simple as saying is this boiler ok for 11 radiators, no-one knows the answer until you do the calcs.
go to a plumbers merchant and get a brochure of radiators that tells you the heat output (if you can get it for your brand that would be great). Now find the radiators that match yours and add up the total power.
It is most likely to be in BTU's and as 1kW = 3412 btu's you have 64,828 btu's to play with... that is a lot.
As a guess, I'd say your rads would be covered by this amount but I could be wrong.
As htg says it's not really that simple as there are a lot of factors to consider, especially if you are going to follow the Part L regs, but that should give you a good rough idea.
I'd be more concerned about the DHW flow rate, sounds like a big house, does a 24kw suffice hot water wise?! (spanner in the works!?)
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