Are more radiators more efficient?
Larger radiators will often be more efficient. This is because they have a larger surface area to radiate heat, so the water inside them doesn’t need to be as warm as in a smaller radiator to generate the same amount of heat.
Is it cheaper to heat just one room?
In smaller homes, it’s almost never worthwhile heating an individual room and is generally better to heat the whole house.
Is it better to have radiators on full?
Regardless of whether you choose to turn your heating on and off, or keep it on at constant low level, minimising the amount of heat lost from your property through better insulation is always good idea. In the long run, doing so will help you save on bills and cause less harm to the environment.