Replacing a radiator with a smaller one

Hi the answer to your question depends on a number of factors. 1.How old is the property? 2.Is it a bungalow ,house or a flat ground floor, upper floor? 3.When was it built, how many external or internal walls, windows & doors 4.Older properties tend to not, have much insulation hence needing bigger radiator size. 5.Is it solid brick construction. 6.Is it cavity wall construction. All room sizes have a U Values and these dictate what size radiator you require for each room then in turn dictate what size boiler require = BTU or kw size. If its an old house lets say with an old radiator you can get convector radiator which is more energy efficient that are smaller in size but can produce heat as good as an old large radiator. Also I would not recommend any sort of radiator cover as it's defeating the object of heating each room in the property or whole of the house it just heats all the walls but not the integrity of the building. Also if you have allot of furniture in all the rooms it takes a long time for rooms to heat up as furniture is dense material. You end up increasing thermostat temperature which in turn use more energy to heat all the rooms up. I hope this will help and assist in what you intend to do all the best and please give me a tick if your happy with the response thanks.

You will not get a better answer than that, well done for spending the time to answer a very under valued and important subject.