Abstract: Heating fluid in a chamber comprising a floor or ceiling and an upwardly or downwardly extending heat receiving wall by positioning a vortex burner substantially at or above the chamber floor in proximity to the heat receiving wall, delivering fuel and air to the vortex nozzle and burning the fuel to make a combustion product, imparting a swirling flow to the combustion product while directing the swirling flow along an elongated path, jetting fuel at a location positioned adjacent the vortex burner, and burning the jet fuel, thereby forming jet flow combustion products that mix with the vortex burner combustion products, and directing the resulting hot mixture generally vertically adjacent to the heat receiving wall for transferring heat thereto.