Abstract: An infra-red heater for treating substrates comprises a gas fired burner having a burner body with a plenum chamber divided by a baffle into an unbaffled upstream intake compartment and a baffled downstream intake compartment. A gas inlet communicates with the upstream intake compartment for supplying a fuel-gas mixture. A fiber matrix is located at the mouth or discharge end of the downstream intake compartment. The burner body includes peripheral side walls having downstream end portions which surround the matrix. The end portions and the matrix are outwardly tapered in the discharge direction.