Abstract: An air-heating gas burner has a housing which includes a fuel gas supply passage and an air supply passage which open into a combustion zone defined between walls which extend downstream of outlets for the gas and air. Combustion products emerging from said combustion zone are confined between further walls which extend downstream to a location at which the combustion process is substantially complete. The burner is intended for mounting in an air conduit and the combustion products emerging from between the further walls have a particularly low content of oxides of nitrogen.