Hi,
I want to change a normal double rad of approx 4300 btu to a vertical designer style rad that will be approx 3000 btu. Will I notice much difference in heat output?

It will still be on a good wall deep in the room and the height will be approx 1800 x 500.
thanks
Paul

Can't really answer that, but you ARE knocking almost 1/3 off the output, so maybe it will............

Best bet is to visit a decent plumber's merchant, and ask them to calculate what output you NEED for that room to keep it comfortable.
They'll want to know things like dimensions of the room, inc height, what the floors are made of, what the walls are made of, any insulation, size of glazing, double or single etc etc.

I've just changed a standard rad for a towel rad for a lady I know. The new rad is about 75% as powerful as the old. So far she reckons she notices no difference, but it has been warm........

Alcazar