Airwash is the term used to describe a combustion-air supply entering the stove at the top of the combustion chamber, near the top of the glass door, which forms a screen of clean air between the glass and the combustion process and keeps the glass clean.

This air supply, often termed "secondary air" is pulled down the glass, by the action of the flue, and into the fuel bed. It continues backward then up the back firebrick and round the baffle or "throat plate" before exiting up the flue as burnt gas.

When burning wood, this is the only combustion-air supply used as wood burns "from top down" and doesn't need air from below.

Smokeless fuel requires cold "primary air" entering the core of the fire from below, via the bottom grate to produce combustion-air and cool the bars. The secondary air "airwash" is used merely to keep the glass clean and has little effect on combustion.

Most stoves have airwash of some sort these days. However this varies from a rudimentary system involving an air inlet at the top of the door, to a sophisticated system which pre-heats the incoming airwash air to such a high temperature that it literally burns contamination off the glass.

Whilst the airwash system is not something easily seen, the design is critical and better manufacturers spend huge amounts of development money getting it right.