Your mirrors become heaters

Why a mirror fogs

Fog is not water settling, it is vapour condensing. It appears as soon as the glass surface drops below the dew point of the ambient air. In a bathroom after a shower the air is saturated and the glass is the coldest surface in the room: that is where condensation happens first.

What makes it go away

All that is needed is for the glass to stay a few degrees above that dew point. It is not a question of power but of constancy: a mirror kept slightly warm at all times never fogs, whereas a mirror heated sharply just before use will arrive too late.

The side effect on service life

What destroys a bathroom mirror is the silvering oxidising at its edges, where moisture works in between the glass and the backing. A back kept dry removes the condition for that oxidation, and that is what extends the mirror's life well beyond ordinary use.

What the room gains as well

A bathroom mirror is often a square metre or more. Once warmed, that surface becomes a radiant emitter facing the occupant, rather than a cold surface taking heat from them. The comfort changes before the air temperature has moved at all.

The safety constraint

The surface temperature is limited to 50 °C, which makes contact safe. That ceiling is not a technical limit but a choice: a mirror is an object people touch, and sometimes an object that draws a child.

Converting an existing mirror is set out on the Mirolia tutorial page, and the product on the Mirolia heated mirror page.