How to replace 1120mm wide radiator?

Adjustable tails:

You are best to leave alone ideally. It might start to leak if you muck about with it. Failing that you are better to get a new one. The old one is virtually certain to have internal corrosion.

Might be an idea to have review/concoct a master plan for the whole system than consider the one in isolation..

Don't forget to flush the system and add new water treatment.

old. I have two questions:

coats of peeling paint. But it works and does not leak. It has no fins. Is it a good idea to replace such an old rad with a modern unit, or should I just clean it up and repaint it?

If it's 50 years old, it will probably last forever even without any inhibitor - they were made of thick sheet steel (and it will be very heavy). With newer radiators, the steel used gets progressively thinner the more recently they were made, and the life of it will reduce if the system hasn't been kept correctly dosed with inhibitor. If it's got any rust spots, particularly at the connections or blanking/bleeding plugs, I wouldn't bother trying to save it. (I also don't like radiators which have been painted, as it's never as good as modern powder coated finish, so that would sway me personally to change it.)

make up for the decrease in width of 20mm?

There are 1/2" radiator tail extensions of various sizes available.

When I was ordering Ultraheat 4 radiators from a local independent plumber's merchant, you could ask for them to be made up any size you wanted. Took 2 or 3 days (instead of next day for the listed sizes), but there wasn't any price premium for doing this.

Note that a finned radiator will have a higher heat output. That might be a good thing if the existing one struggles in its current location. However, it might be a bad thing if that's the radiator in the room with the house thermostat, as it will heat up the room faster and switch off the boiler before other rooms have heated up. You could select one with a different height to change the heat output, if you want to keep to roughly the same length.

If you do get a new radiator I have found PlumbNation good. The thing ends up being delivered from your local Plumb Center but costs a lot less than if you'd gone into Plumb Center and bought one off the shelf.

s old. I have two questions:

coats of peeling paint. But it works and does not leak. It has no fins. Is it a good idea to replace such an old rad with a modern unit, or should I just clean it up and repaint it?

There's no knowing which will last longer, the old or a new one.

k to make up for the decrease in width of 20mm?

As its only 20mm, an adjustable tail. The other option, if the pipe runs si deways, is to cut & rejoin the pipe.

NT

just clean it up and repaint it?

make up for the decrease in width of 20mm?

NT

old. I have two questions:

coats of peeling paint. But it works and does not leak. It has no fins. Is it a good idea to replace such an old rad with a modern unit, or should I just clean it up and repaint it?

make up for the decrease in width of 20mm?

sideways, is to cut & rejoin the pipe.

If there's underfloor access, plastic pipe? In that way the pipes can be fed behind the skirting, making for a neater job and a clear floor.

Rob

being delivered from your local Plumb Center but costs a lot less than if you'd gone into Plumb Center and bought one off the shelf.