Heat Pump Types & Systems

The most common type of heat pump is an air-source heat pump. This type of system absorbs heat energy from the air and transfers it through refrigerant lines. At moderate temperatures, air-source heat pumps can operate at up to 300 percent efficiency, delivering three times more heat than the electrical energy they consume.

Breakthrough technology for cold climate performance

Historically, residential air-source heat pumps were primarily used in areas where air temperatures did not drop below 40°F. However, tremendous improvements in technology—such as inverter-driven compressors—have rendered a new generation of air-source heat pumps that can deliver heat efficiently and reliably at much lower temperatures:

• Ductless systems: As low as -15°F
• Ducted systems: As low as 5°F

Whether configured as a ductless or ducted system, heat pumps rated for cold climates are the quietest and most advanced models on the market. Unlike other air-source heat pumps, these systems provide consistent temperatures and the greatest electric savings by self-adjusting their speed and capacity for heating (and cooling), depending on the outdoor and indoor temperatures.

Traditional furnaces turn on and run at maximum capacity until the temperature in a home exceeds the thermostat setting, then the furnace turns off. Once the temperature inside a home drops below the thermostat setting, it then turns back on. Sometimes these systems can be quite loud when running, and many times occupants might be too hot or too cold.

In contrast, a heat pump with an inverter will start up slowly. This reduces noise and keeps lights from flickering. It will meet the new temperature set point as quickly as possible for optimal comfort and will maintain the desired temperature in a home. How? By providing a constant stream of warm air at a low volume for long periods of time. Homeowners may not hear the unit operate or feel blasts of hot air, but as long as a thermostat shows the desired temperature they can be sure it’s working.

Since temperatures can drop quite low during winter in Michigan, cold climate heat pumps are one of the best available options for affordable year-round heating and cooling.

Manufacturers typically have a cold climate line of products that are best suited for operation in low temperatures. When comparing systems, homeowners should keep an eye out for labels from manufacturers that indicate strong performance in cold climates.

The Northeast Energy Efficiency Partnerships (NEEP) works in states such as Vermont and Maine which experience comparable winters to Michigan. This organization has developed a set of performance requirements which require specific efficiency levels in both cooling and heating modes, including heating performance at 5°F. NEEP maintains a list of air-source heat pump models that meet their cold weather performance requirements. Visit ashp.neep.org to access the list. Homeowners should check to see if an air-source heat pump appears on this list to ensure they are getting a system that’s best prepared to deliver heat efficiently in Michigan’s cold climate.

One configuration for an air-source heat pump is a ductless system. Ductless heat pumps include three main components:

• Outdoor unit that typically sits elevated off the ground or mounted on an exterior wall—smaller than a standard central air conditioner
• Indoor unit mounted high on the wall or at floor level, or concealed mini ducts located in attic or crawl space
• Remote control thermostat

Ductless systems with more than one indoor unit (multi-zone) allow for different temperature settings throughout different parts of a home (zones)—providing optimum comfort for the entire family while ensuring energy isn’t wasted where it isn’t needed.

Ductless Heat Pumps

Mini-duct heat pumps

This is another configuration of a mini-split heat pump. The outdoor unit remains the same, however the indoor units are wall or ceiling mounted registers. New smaller diameter ducts with short distances are connected to the unit and hidden in the attic or floor. These systems are ideal for bedrooms where one wall-mounted indoor unit would provide too much heat or cooling for the room. These systems allow homeowners to provide space conditioning to a few rooms located near each other without the need for individual wall-mounted units in each room. Instead, you have a traditional looking floor or ceiling register in each room with one centrally located thermostat.

A ductless system is ideal for:

• Homes utilizing electric baseboard heat, steam or hot water heat, wood-burning stoves, or wall heaters
• Homes without ductwork
• Homes with open floor plans
• Rooms with poor air distribution/uneven temperatures
• New construction or new room additions
• Manufactured homes
• Reducing reliance on propane or fuel oil

Installing a ductless heat pump system is quick and non-intrusive: A professional contractor can usually complete installation in less than one day. Only a small three-inch hole in an exterior wall is needed to connect the refrigerant line from the outdoor unit to the indoor unit.

Ductless air-source heat pump systems can be 15-20 percent more efficient than ducted systems because a large blower motor is not needed to blow conditioned air throughout a home, and risk of air leakage in the ductwork is eliminated.

Since heat pumps draw renewable heat energy from the outdoor air, they must work harder as temperatures fall—impacting efficiency. For example, while the most efficient air-source heat pumps can operate at up to 300 percent efficiency in moderate temperatures, the same models may achieve an average heating season efficiency of about 250 percent—which is still excellent, considering conventional heating sources cannot exceed 100 percent efficiency.

While heat pump technology is advanced enough to function in below freezing temperatures, many Michigan homes with air-source heat pumps may need supplementary heat for the coldest days and nights of winter. During these times, the heat pump will not run as efficiently, and may not provide as much heat as is needed.

Electric Baseboard

Supplemental heat can come from a variety of sources, such as an existing furnace or boiler, electric baseboards, wood burning stoves, or even space heaters in the most frequently occupied areas of a home. Conveniently, ducted heat pump systems can easily integrate with most newer gas furnaces, just like a central air conditioner would.

Wood Burning Stove

If a home already has an air distribution (ductwork) system, owners may consider a ducted heat pump. Ducted heat pumps include four main components:

• Outdoor unit that resembles a standard central air conditioner
• Indoor unit, most often placed with the furnace
• Ductwork
• Advanced thermostat

In this application, conditioned air travels through a home's existing ductwork. Although it’s best to install a new furnace and heat pump at the same time as a matched set for optimal efficiency, in some cases, a heat pump can be added on to a home's existing furnace. When the heat pump is being used, the furnace functions simply as an air handler (to move air through the ductwork).

Ducted Heat Pumps

A ducted system is ideal for:

• Homes with existing ductwork
• Introducing central air conditioning
• Replacing a central air conditioner and/or furnace
• Reducing reliance on propane or fuel oil

Installing a ducted heat pump is similar to installing a central air conditioner, and can be completed in one day. Homeowners should discuss with their contactor to ensure all required components are compatible.

All-electric ducted heat pump systems

All-electric ducted heat pumps contain built-in electric resistance coil heaters that can operate simultaneously with the heat pump, to provide 100 percent of a home’s heating needs on the coldest days. If the goal is to eliminate gas entirely, this is a good option. An existing gas furnace would be completely replaced with the new heat pump and air handler.

All Electric System

Dual-fuel ducted heat pump systems

A system with backup natural gas or propane is another option for providing supplemental heating. Like a central air conditioner, in this configuration, the heat pump is often attached to the top of the gas furnace.

In the winter, when the outdoor air cools to a predetermined temperature, the electric heat pump shuts off and the gas furnace takes over—supplying heat as the conventional furnace homeowners are used to. You can also manually control which heating source is used to minimize heating costs.

To decide whether an all-electric or dual-fuel ducted heat pump is right for them, homeowners should consult with their HVAC contractor. In either case, homeowners should be sure to purchase a cold climate heat pump to maximize the time the system operates in heat pump mode—which will provide the greatest energy and cost savings.

Dual-Fuel System

Another type of heat pump is a ground-source (or geothermal) heat pump. Instead of drawing heat from the outdoor air, heat is absorbed from the earth (or ground water).

Ground-source heat pumps can provide both heating and cooling for the home and, in some instances, supply domestic hot water and dehumidification. They can operate at up to 500 percent efficiency, delivering five times more heat than the electrical energy they consume.

Ground-source heat pumps feature four main components:

• Underground heat exchanger (ground loop) or groundwater source
• Indoor unit, typically placed in the basement or where a furnace is located
• Ductwork or hydronic (hot water) heating system
• Thermostat

Generally, there are two different types of ground-source heat pumps: Open loop (which use an existing or new water well) and closed loop (a loop of pipes in the ground or body of water, placed below frost level).

Open Loop

In open-loop systems, water exiting the heat pump can be drained into the ground, a well, pond, etc. (in compliance with local codes).

Closed Loop

A ground-source heat pump system is ideal for:

• Homes with a pond, well, or land available for excavating or drilling
• Homes with existing ductwork or a hydronic heating system
• Introducing central air conditioning
• Replacing a central air conditioner and/or furnace
• Reducing or eliminating reliance on propane or fuel oil

Despite fluctuations in seasonal air temperatures, the soil and water just a few feet below the Earth’s surface remain at a relatively constant temperature. This enables ground-source heat pumps to deliver sufficient heat on the coldest winter days, and to operate at higher efficiencies than air-source heat pumps.

While ground-source heat pumps are more efficient and typically do not require a backup heating system, they do cost more upfront and may require excavation. There are pros and cons to each type of heat pump, and many factors—such as budget, current heating system, and the characteristics of a property—will determine which option is best for a home.