[secutanudu]

It depends how your system is set up. Can you see if that radiator was fed with a tee off the main line or with elbows? (does the main line go throught he radiator, or does it branch off?)

If tees, can you see if they say "monoflo" or anything else on them?

 

[secutanudu]

If his old radiator was fed with a monoflo tee, hs main line will be left with restricted flow if he caps the pipe that used to feed the radiator.