What size radiator to buy - how close to current does it need to be for DIY switch?

[Greenscarf1]

Changing older radiators and thought if we got the same size it would be most straightforward. DH thinks he can do himself. But nothing is the same size! How difficult is it to fit one a slightly different size, is this a professional job?

I would calculate if the old ones are the correct size for each room. We have had double fin ones installed. I would not DIY as pipe entry can be in a different place. It can look awful if it’s not done properly.

Plumbing is not that tricky DIY. If you want to do a straight swap then the pipe centres need to be within a few mm of the current radiator. However, moving a pipe isn't all that tricky but you would need to drain the water out of the radiator system cut and move the pipe and the connect it up again. Worst case you end up getting sprayed with black water from the radiator and end up having no heating for a couple of days while you wait for a plumber. Best case, you get a radiator changed without paying £500. Depends how much your time is worth i guess?