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. A monitor, which includes a timer, is responsive to the pressure sensed in order to determine that the pressure differential has decreased below a predetermined level for more than a predetermined length of time. A temperature and pressure changeover control responds to the monitor in order to lower the temperature setpoint to the lower temperature setpoint level and adjust the proportion of air drawn from outside the space to air drawn from within the space in a manner that decreases the proportion of outside air when the pressure differential has decreased below a predetermined level for more than the predetermined length of time. |
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