Replace Old Radiators?

We've recently been told that, if we replaced our 20-year-old radiators with modern equivalents, our heating system would perform better. I'm interested in looking into this before shelling out the hard-earned. Can anyone point me in the direction of a source where I can obtain info on the heat output of my old radiators?

For info, the radiators are generally two panel units, but have no convectors between the panels, and a very narrow gap at the top/bottom.

What is the symptom of the problem that you wish to get fixed?

Despite the fact that the radiators are warm/hot, the rooms aren't. It is an old house, but we have double glazing and reasonable loft insulation. The existing radiators are generally about 1500mm long, and therefore would be difficult to replace with bigger. The questin is therefore, can we replace with more efficient?

As you say no convectors compared to modern radiators which have means they emit more heat.

Modern radiators may not be made of as heavy grade steel but do emit heat quicker however do cool down quicker too.

Depending on how old and the condition of the system they may also be corroded inside and full of magnetite and so have lost alot of there effeciency.
If you are to replace the rads do a flush first with the old rads off either power or chemical additive over a few weeks.

Good luck
Pete