The efficiency of a radiant ceiling

Efficiency does not mean the same thing everywhere

For an electric convector, conversion efficiency is one hundred per cent: all the current becomes heat. That figure therefore says nothing, since it is identical for every electric appliance. The real question lies elsewhere: how much of that heat actually reaches the occupants.

Where the heat that does not arrive goes

It goes into the air, which rises to the ceiling. It goes into the cold surfaces, which absorb it. It goes out through airtightness defects, with the air it has warmed. A system can draw six thousand watts of which only half does anyone any good.

What radiation removes

A radiant ceiling emits towards surfaces and people without going through the air. There is no intermediate transport, and therefore no losses on the way. That shortcut, and not a better conversion efficiency, is what explains the difference in consumption observed.

The effect of passive recovery

The closed, insulated plenum recovers the heat produced in the room by the occupants, the cooking, the lighting and the appliances, and sends it back down. That share is not produced by the system: it is simply given back instead of being lost.

How it is verified

With a thermal camera and a meter, over a full season. A single measurement proves nothing, because it depends on the outside temperature that day. It is the reading over several months that allows a conclusion.

The cost of an installation is on the how much does a radiant ceiling consume page, and the recovery principle on the page about passive heating.