A heat pump is an air conditioner capable of also providing heating for your home by reversing the normal flow of refrigerant (freon) within the system.

How Does A Heat Pump Work?

To understand the operation of a heat pump, one must understand some basic principles of refrigeration. When air conditioners operate to cool our homes, they are not adding cool air, they are removing heat. The typical air conditioning system consists of three components which work together to move "heat" from one location (inside your home) to a more desirable location (outdoors).

the condenser	is responsible for discharging the heat and is located outdoors
the evaporator	absorbs heat from inside the home and is located at or near the indoor blower
the blower	circulates air through the evaporator for heat to be removed

Refrigerant or freon is the medium by which the heat is carried from the evaporator to the condenser. During the cooling cycle the compressor (located in the condenser) compresses the heat-laden refrigerant returning from the evaporator and discharges it into the condenser coil. The fan pulling air across the coil removes the heat and discharges it to the outdoor air.

Once the heat is removed, the refrigerant condenses (changes from a gas to a liquid) and travels back to the evaporator. Once it reaches the evaporator it passes through a very small opening known as an orifice or a metering device. The extreme pressure drop created by the orifice causes the now-liquid Freon to "evaporate" and again become a gas. When a liquid evaporates it absorbs heat, much like getting a chill when stepping out of a swimming pool. The cycle is repeated over and over again and ends only when enough heat has been removed to cycle the thermostat off.

The Heating Mode

To provide heat from this same unit the evaporator and condenser must essentially switch places. That is, heat must be moved from the outside air to the indoor coil for discharge. This is accomplished by reversing the flow of refrigerant through a device found in heat pumps knows as a "reversing valve." This valve is automatically controlled through the thermostat when switched to heat.

Yes, there is usable heat in outdoor air at temperatures as low as 17 degrees Fahrenheit. As the temperature of the outdoor air decreases, however, the heating capacity of the heat pump diminishes proportionately, resulting in lower discharge air temperatures at the air registers, and gradual cooling of your home. To supplement the heating capacity of the heat pump, electric resistance heating elements are used and automatically engage via the thermostat when this condition occurs.

Heating Mode

Cooling Mode

Why Not Just Use Electric Heat?

A heat pump makes more efficient use of electrical energy than electric resistance heating. Heat removed from outdoor air coupled with heat created by the compressor when running can average two to three times the amount created by resistance heat alone. One kilowatt hour (KWH) of electricity input to an electric resistance heater produces 3, 413 BTU per hour of heat. 1 KWH input to a heat pump with a "coefficient of performance" ("C.O.P.") of 2.5 produces approximately 8, 533 BTU per Hour. This more efficient use of electrical energy keeps heating costs down. To optimize the efficiency of your heat pump an "outdoor thermostat" can be used to insure the supplemental resistance heater inherent in your heat pump operates only when necessary.

Environmentally Friendly

Heat pumps reduce the amount of fossil fuel that needs to be burned to keep homes warm or cooled, thereby decreasing the amount of pollutants entering the earth's atmosphere.

Less Dryness in Warm Air

Because heat pumps do not use an open flame to create heat, less moisture is taken out of the winter air, making the home more comfortable for humans, and also better for fine wooden furniture.

Frequently Asked Questions

Q. Will a heat pump provide all the heat needed in the winter?

A heat pump ordinarily becomes less effective below 35 to 40 degrees Fahrenheit ambient temperature. Below that, it may be necessary to supplement the heat provided by the heat pump. (See "Why Not Just Use Electric Heat" above.)

Q. How expensive are heat pumps?

A. The initial cost of heat pump equipment can be 10-15% more than units which use natural or LP Gas for heating, but this difference is minimal when compared to the cost of natural gas or LP Gas service setup.

Q. Do heat pumps have to exchange heat with outside air?

A. No. Different models of heat pumps can exchange heat with ground water, making them less susceptible to outside air temperature. However, ground water heat pumps are somewhat more expensive to install.

Q. What's the difference between a SEER rating and a HSPF rating on a heat pump?

A. The SEER rating is the Seasonal Energy Efficiency Rating, and is a measure of the cooling efficiency of a heat pump or air conditioner. Federal regulations on 1/1/06 will require a SEER of 13 or more for new air conditioners or heat pumps. However, some models score much higher than the minimum, meaning they will save many more energy dollars.

The HSPF is the Heating Seasonal Performance Factor which measures the heating efficiency of a heat pump. Federal regulations on 1/1/06 require a HSPF of 6.8 or more for new units. As with SEER ratings, the higher the HSPF, the more energy dollars the heat pump will save.

Q. How do I know if my electric heat is on when I'm using my heat pump?

A. Most heat pump thermostats have a small light or icon which lights when the supplemental electric heater is in use. This light is normally labeled "AUX HT" for auxiliary heat.

Q. What does the EM HT switch do?

"EM HT" stands for "emergency heat." When this switch is in the on position the heat pump (the unit outdoors) is turned off and the electrical supplemental heater becomes the sole source of heat. This switch is used only if your outdoor unit (the heat pump) is not working or needs service. The red EM HT heat light or icon on your thermostat will light when this switch is on.

Q. On real cold days, my heat pump sometimes has steam coming out of it. Why?

A. When this condition occurs, your heat pump is going through a "defrost" cycle. The outdoor coil can ice over during cold wet days. When this occurs, the defrost control senses it and automatically initiates a defrost cycle. To accomplish defrost, the reversing valve is switched and the unit is actually in the cooling mode momentarily. The hot refrigerant gas now flowing through the outdoor coil melts the ice away, and the resulting steam is created by the evaporation of the water. A defrost can last one to 10 minutes depending on the unit and the conditions. During this period the electric supplemental heater is automatically activated to temper the indoor air. Expect slightly cooler discharge air during this period.