A bathtub having a water pump and heater for heating and circulating water from the bathtub to at least one mixing chamber, an air blower and heater for delivering heated ambient air to the mixing chamber, and a plurality of orifices for delivering an air-water mixture from the mixing chamber to the bathtub. A wall of the mixing space may be associated with a wall of the bathtub, and the orifices may be in the wall providing direct fluid communication between the mixing space and the tub. The invention provides improved thermal stability and eliminates evaporative cooling effects in air-injected tubs.