Replacing an old radiator - what do I need to look for in the replacement?

Before buying you need to work out the BTU for the room.The one you are replacing might not have been the correct one in the first place. Hope that helps

Yep you are on the right tracks, some other things you might want to consider, is the pipework supplying the radiator in good condition, will the existing valves be suitable? Maybe you might upgrade to thermostatic radiator valves that will save you money because they are energy efficient. Other things you might want to consider are, was the existing radiator size capable of heating the room to the correct level?, did the existing rad have cold spots? You may be wise at the same time drain the heating system and power flush with chemicals to remove any sludge before fitting a new rad, also refill and treat with a corrosion inhibitor to protect the complete system including the boiler. Hope this helps…

I agree check your btu s but I always advise to go bigger than the btu calculator states. It’s easier to turn a radiator down then make it produce more heat.