Abstract: A control for an air treatment unit, such as a space heater having a heat source and an air handler that draws air from outside the space and from within the space in order to form a combined stream of air that is discharged to the space. The control includes a temperature setpoint control adapted to controlling the heating source in order regulate air temperature in the space to a particular air temperature setpoint and a temperature setpoint setback control that is adapted to decreasing the air temperature setpoint to a lower temperature setpoint during periods when it is anticipated that the space will be unoccupied. A differential pressure sensor senses a pressure differential between the space and outside of the space. A pressure control is responsive to the pressure sensor in order to control the proportion of air drawn from outside the space to air drawn from within the space.