Replacing old rads with modern

[Vikki]

The central heating in my house is a real mish-mash. The boiler is an Ideal combi fitted 3 years ago. Most of the radiators are really old, with the small bore pipe. I've replaced 3 upstairs radiators out of necessity.
Now I want to replace two massive radiators downstairs. They are really old and grotty single 6-foot ones. I think I can replace them with smaller (say 4 foot) double radiators in a modern style. Not sure if I can mention trade names on this forum, but the new rads I'm thinking of are those with the grills around top and sides so they look really flush.
Does anyone have any views on the viability of this? Will the changes in pipe diameter start to affect the efficiency of the whole system?

 

[taydo]

Do you need to change the pipe size

 

[Vikki]

It was my understanding from having the upstairs radiators changed that modern rads were made for a larger pipe, whereas my pipe is 15mm. Maybe I'm confused with something else in this moneypit of a house, be pleased if I am!

 

[taydo]

The standard domestic rad valve is 15mm so I dont see you having a problem changing radiators.

 

[oilman]

15mm is fine, except under exceptional circumstances, the radiator valves will be open only a small proportion of the pipe area.