"Clive Arthur" wrote in message
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On 06/05/2021 12:55, jon wrote:

What is this nonsense, heat is dissipated by radiation, convection or
conduction so how come efficiency becomes a problem.

It is true (though 'effective' would be a better word) because of the
reasons given by T i m and others. Look at the manufacturer's figures for
power output and you'll see.

As a result, a vertical rad will be heavier and (usually much) more
expensive. The upsides are that they take up less width, and when you
come in from the cold you can stand against one.

I preferred to sit on the horizontal one in that situation.