Linda has the details covered on that one, even thought they are radiators, convection is the key. Open vents on top are impotant and air draw at the bottom just as important. The face could also have an old fashion metal screen that allows heat out to the front. Looks like the radiator is mounted up high? Might just be the pic. Here is a cover I made not too long ago. We opted for just top grates as per the designer but I personally would have allowed some vents on the face too.
Q