how do i add another radiator to my central heating system

[GIT]

How do I go about installing another radiator to my existing central heating system.
I think my central heating system was installed in the late 70's early 80's its an open vented system but I'm not sure if it will still be a reversed return system (2 pipe parallel) or being a 70's installation a one pipe ring system.
I can do the necessary radiator installation no trouble I just need some advice as to what sort of central heating system I have!
any help will be much appreciated.

 

[taydo]

are there any exposed pipes feeding the radiators in loft under floorboards etc. there two or one?

 

[GIT]

No - theres no way of telling really as nearly all my floors are either nearly new carpeted or I'v put wooden flooring down over the floor boards and I'm not gonna start ripping up flooring now - I'm trying to avoid that !.
I'm sure my systems a reversed return like nearly all central heating systems are so i'm gonna go with that.
I just wanted to make sure before conecting new pipe work to old.
Cheers !