Another heated ceiling in a bathroom

The bathroom with no window

It combines three difficulties: it can only be ventilated mechanically, it has no solar gain, and it often backs onto colder rooms. That is the configuration where damp settles fastest, and where heating and ventilation have to be thought out together.

The dew point, in practice

A surface condenses as soon as it drops below the dew point of the ambient air. After a shower the air is saturated: everything cold becomes covered in water. The answer is therefore not to extract more, it is to remove the cold surfaces.

What the ceiling changes

A radiant ceiling warms the surfaces by radiation rather than the air by convection. Walls and ceiling stay above the dew point, condensation no longer finds anywhere to form, and grout lines and corners stop blackening.

What remains the job of the ventilation

Extracting the moisture produced is still essential: heating does not replace ventilation, it removes the place where the moisture settles. A clogged terminal or an insufficient flow cancels most of the benefit, whatever the heating system.

The order in which to work

Check the extract flow first, treat the ceiling second. The other way round, a ventilation problem gets blamed on the heating, and people wrongly conclude that the system does not work.

Sizing for short use is dealt with on the page devoted to it, and the effect of radiation on moisture on the page about the air you breathe.