Thanks all for your reassuring feedback. I've assembled my rack and it now
works - no smoke!.

Only thing is results are a bit disappoiunting so far (or perhaps my
expectations were to high). At first I tried 80mm 1000 rpm fans, very quiet
but didn't really blow much. Perhaps might add a couple of drgrees during
continuous use but I'm aiming to turn my 1000 x 700 stelrad K2 double
convector into a big fan heater for fast warmup on cold frosty days. I put a
shelf over the rad to stop the hot air going straight up to the ceiling.

Since hen I've tried 2 x 2500 rpm fans . You can feel a breeze rather than a
blow with your hand at the top of the radiator, helpful but not quite what I
wanted and a bit noisy even running on reduced voltage. I fear the answer is
probably more fans (or fit a 9W Zantec(sp?) Tornado fan. I'll probably end
up with two under-radiator boxes, a quiet 1000 one for continuous use if
needed and a noisy power-booster. Then all I've got to do is to put it on
'Dragon's Den' ;-).

Skeggy