kitchen radiator

I would think 500W is adequate for a small kitchen with a boiler..and decent insulation.

That's about what a kickspace puts out IIRC.

Out vast kitchen is totally OK with less than 1 Kw of Aga..Ok thats on

How long is a piece of string? It depends on the size of kitchen, the construction, number and size of windows, etc., etc. Most on-line calculators are pretty crude - and don't tell you how they arrived at a particular number. You need to get hold of a half-way decent heatloss calculation program which runs on your PC, and which allows you to control all the important parameters - such as those provided by Barlo or Myson.

Depends on the boiler. If you have a modern high efficiency boiler, there should be very little heat leaking into the room.

Not unless you tell it about other sources of heat! And on-line calculators probably don't allow you to do that.

They can be almost anywhere - kitchen, utility room, behind a gas fire(!), garage, airing cupboard, attic, outhouse - the possibilities are legion, and it often depends on what is convenient in a particular case.

Yes, unless space is tight - in which case it's better to have the *right* size of rad.