Heated ceilings in rooms with high ceilings

The point where heating the air becomes absurd

In a room 2.50 m high, heating the air works well enough. At 4 m, half the heated volume sits above people's heads. At 6 m, you are paying to keep at temperature a layer of air nobody will ever reach. Height turns a minor flaw into a chasm.

What radiation changes about the question

A radiant emitter does not heat the volume, it heats the surfaces and the people it can see. The height of the space therefore costs nothing in energy: it only changes the distance between emitter and target, and so the power per square metre required.

The limit of the method

The intensity received falls with distance. Beyond a certain height a low temperature radiant ceiling is no longer enough, and you must either increase the emitting area, or lower the emitter, or raise the temperature, which moves towards industrial radiant heating.

The trade-off in practice

It is made by calculation, height by height, and there is no universal rule. What matters is asking the question in the right order: height and use first, technology second, never the other way round.

The part insulation plays in these volumes

The larger the volume, the larger the loss surface. Closing and insulating the plenum therefore pays back better than in an ordinary room, because the heat recovered is proportional to the surface, not to the volume.

A real job at 6.50 m is told on the page about large volumes, and the case of a public space on the toy library page.