Heat pumps replace furnace and central air conditioning equipment with a single heating-cooling system that "pumps" heat into the building in the winter and to the outdoors in the summer. Most heat pumps are compact two-piece units with both indoor and outdoor components. Single-package units are installed entirely outdoors. In size and appearance, a heat pump looks like a central air conditioner.
A heat pump can supply significantly more energy than the energy it uses, depending on the efficiency of the heat pump and the geographic location.
Most heat pumps have an outdoor unit (called a condenser) and an indoor unit (an evaporator coil). A substance called a refrigerant carries the heat from one area to another. Geothermal heat pumps use the relatively constant temperature of the soil or surface water as a heat source and sink for a heat pump, which provides heating and cooling for buildings. Ground-source heat pumps use a buried loop or coil of tubing to exchange heat with the soil in the yard. Water-source heat pumps use a loop of tubing submerged in a nearby lake or pond. Electric air-source heat pumps, often used in moderate climates, use the difference between outdoor air temperatures and indoor air temperatures to cool and heat a home.
The cooling performance of heat pumps, like that of central air conditioners, is rated by the Seasonal Energy Efficiency Ratio (SEER), which describes how many Btu per hour of heat are removed per watt the heat pump uses, adjusted for a representative seasonal cooling load. The higher the SEER, the more efficient the heat pump is at cooling.
Heating performance is measured by the Heating Season Performance Factor (HSPF), which is the estimated seasonal heating output divided by the seasonal power consumption for an average U.S. climate. The higher the HSPF, the more efficient the heat pump is at heating.
The current national efficiency standard for new heat pumps requires a minimum HSPF of 6.8 and a minimum SEER of 10. For the most efficient equipment, the American Council for an Energy-Efficient Economy (ACEEE) recommends SEER at least 14.5 and HSPF in the range of 9.0.
15 & above
12.5 & above
9.0 & aboveSEER - Seasonal Energy Efficiency Ratio
EER - Energy Efficiency Ratio
HSPF - Heating Seasonal Performance Factor
Geothermal Heat pumps are durable and require little maintenance. Most components are underground, sheltered from the weather. The underground piping used in the geothermal system is often guaranteed to last 25 to 50 years and is virtually worry-free. The components inside the house are small and easily accessible for maintenance. Warm and cool air is distributed through ductwork, just as in a regular forced-air system. ENERGY STAR qualified geothermal heat pumps use about 40 to 60% less energy than a standard heat pump, and are quieter than conventional systems.
ENERGY STAR qualified air-source heat pumps have higher SEER and HSPF than standard models, which makes them about 20% more efficient than standard models. (See table below from DOE's Federal Energy Management Program.)
Annual Energy Use
Annual Energy Cost
Lifetime Energy Cost
Lifetime Energy Cost Savings
In warmer climates, SEER and EER are more important than HSPF; in colder climates, HSPF is more important.
For the most efficient equipment, purchase pumps with a SEER of at least 14.5 and HSPF in the range of 9.0.
Not a stand alone system. Heat pumps operate very inefficiently at sub-freezing temperatures, so avoid them as stand-alone heating systems in cold climates.
Compare heating fuel costs. In climates with mild winters, heat pumps may provide cost-effective heating when compared with gas or oil furnaces, depending on relative fuel costs.
Do not oversize. Over-sizing heat pumps, besides raising purchase cost, results in weaker energy efficiency, poorer humidity control and shorter product life, all due to excessive on-off cycling.
Gauge your heating and cooling requirements. Since heat pumps perform both heating and cooling, pay special attention to identifying the heating and cooling requirements separately.
Check your ducts. Leaky ductwork is a particular problem with heat pumps since heat losses will cause the electric resistance or "back-up" heat to operate much more frequently; consider sealing ducts in conjunction with installing the heat pump.
Choose and set the controls properly to prevent energy losses with heat pumps; pay careful attention to minimizing operation of the back-up heating.
Consider an energy efficiency mortgage. In a new home, the additional payment on your mortgage for an efficient heat pump is usually less than the savings on energy bills. For example, a geothermal heat pump system costs about $2,500 per ton of capacity. The typically sized home would use a three-ton unit costing roughly $7,500. That initial cost is nearly twice the price of an air-source heat pump system that would probably cost about $4,000, with air conditioning. If the extra price of a heat pump system is included in an energy efficiency mortgage for a new home, the homeowner could have a positive cash flow from the beginning. The extra $3,500 cost of the more efficient system may add $30 per month to each mortgage payment, which is offset by the homeowner's utility bill savings.
The current national efficiency standard for new heat pumps specifies a minimum HSPF of 6.8 and a minimum SEER of 10. In 2006, a new standard will take effect, but the final performance levels have not been set because of ongoing litigation. Refrigerants with ozone-destroying chlorofluorocarbons (CFCs) were used many years ago in heat pumps, but almost all equipment on the market today uses HCFC refrigerants, which have a much lower ozone-depleting effect. There are a few heat pump models now on the market (with more coming) that use refrigerants with no ozone-depleting effect; ask your supplier for information.