I have noticed in several places I have been recently, radiators installed just above some boxed in pipes. Now the bottom of the rad is almost touching the boxing (Like maybe 2mm ish gap), surely this will reduce the efficiency of them quite considerably wouldn't it?
Sparks...
Strictly speaking the efficiency will be 100% unless on an outside wall. In which case it will be marginally less efficient as it will have to run a little hotter to do it's job. This is turn will make the wall hotter increasing its heat losses a little.
However, you probably meant that the restriction to the air flowing by convection will cause the radiator not to work as well? This will make a marginal difference as the air will have to enter at the sides. This will only be significant if the radiator is marginally undersized. and in the coldest weather. Most installers usually allow plenty of extra capacity for the radiators so you should be OK.
What really makes a difference is putting the rads in fancy MDF boxes, This reduces the output available to about half.
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