p.s.
(will I never stop?)
A single radiator, 1 metre long x 500mm high, has an output of about 875W under ideal conditions, and a double rad 2 metres x 500mm about 2400W, so although builders tend to fit quite small radiators (to keep costs down), calculated from the heat-loss tables, if you want to heat a house quickly, from cold, in cold weather, you need to push more heat in than will be needed to maintain the temperature. If the rads are fitted with TRVs, they will throttle back the output as it approaches target temperature, so you will not be overheated or waste energy. Bigger rads will also maintain the room temperature at lower flow temperatures, so a modern condensing boiler will run more efficiently and quietly, as it will adjust its flame size and fan speed down.
I used to be away on business a lot, so I changed all my rads from singles to finned doubles, and the house heats up much quicker from cold. My modern boiler modulates down from 24kW max to 8kW min, and starts reducing its power after about 20 minutes if the house has become cold.
In sub-zero temps like -15C last winter, my house uses over 15kW to keep it warm, although the boiler sizing calculator will tell me I only need 11kW. Remember the calculator is based on an outdoor temp of -1C which is not very cold. Radiators based on the heat loss calculator would have been unable to deliver enough heat to keep the house warm