A two-stage heat pump has a compressor which is capable of operating at a high and low speed, improving its ability to maintain the temperature in a home with greater precision. This type of HVAC system also offers the advantage of more economical heating and cooling.
When the thermostat of a dual-stage heat pump senses the need for cooling, it starts the unit at full speed. Once the temperature approaches the thermostat setting, the unit switches to a lower stage and continues to operate. This allows the unit to compensate for heat gain in the home without cooling the space below the desired temperature. If daytime heating begins to overpower the lower cooling stage, the compressor returns to the higher speed to counteract the additional heat.
The dual stage unit helps to eliminate the wide temperature swings associated with single-stage heat pumps. The single-stage unit operates at full speed or turned off. While the average temperature in the room is the setting of the thermostat, they vary several degrees as the unit cycles.
The additional initial investment is relatively small for the cost savings realized. A two-stage heat pump costs approximately $250 more at the time of purchase. However, it improves efficiency by as much as 40 percent.