Air-Source Heat Pumps
An air-source heat pump transfers heat between a building and the outdoor air, providing both heating and cooling with the same refrigeration system.
It is the most common residential heat-pump type in the United States. The system can distribute conditioned air through central ductwork or through one or more ductless indoor units.
Because a heat pump moves heat instead of generating all of its heat directly from electric resistance, it can deliver more heating energy than the electrical energy it consumes under normal operating conditions.
Sources: DOE - Pump Up Your Savings with Heat Pumps, ENERGY STAR Air-Source Heat Pumps
How Does an Air-Source Heat Pump Work?
An air-source heat pump uses a compressor, refrigerant, heat exchangers, and fans to move heat.
In cooling mode, it works much like a central air conditioner: the indoor coil absorbs heat from the house and the outdoor coil releases it outside.
In heating mode, a reversing valve changes the refrigeration cycle so the outdoor coil absorbs heat and the indoor coil releases that heat into the home.
The outdoor air does not need to feel warm to contain usable thermal energy. The practical limit is determined by the heat pump's design, compressor, refrigerant cycle, controls, and the amount of heating capacity the unit can maintain as outdoor temperature falls.
What Are the Main Types of Air-Source Heat Pump?
Residential air-source systems usually fall into four useful groups.
Ducted central heat pumps
A ducted heat pump uses a central indoor air handler or matched indoor coil and moves conditioned air through ducts.
This is usually the first system to quote when an existing house already has usable forced-air ductwork.
Ductless mini-splits
Ductless systems use one or more indoor units instead of a whole-home duct network.
They work particularly well for homes without ducts, additions, garages, isolated problem rooms, and zoned retrofits.
Ductless mini-split heat pumps
Cold-climate heat pumps
Cold-climate systems are air-source heat pumps designed and certified for stronger low-temperature performance.
ENERGY STAR's current Cold Climate designation includes minimum efficiency, 5°F COP, and 5°F capacity-retention requirements.
Dual-fuel systems
A dual-fuel system pairs an air-source heat pump with a gas or oil furnace.
The controls determine which heat source operates under different conditions.
What Efficiency Ratings Matter?
For residential air-source heat pumps, the three core ratings are:
SEER2 - seasonal cooling efficiency.
HSPF2 - seasonal heating efficiency.
EER2 - cooling efficiency at a specified test condition rather than across an entire season.
Current ENERGY STAR criteria for residential split-system heat pumps are:
| Metric | ENERGY STAR split-system minimum |
|---|---|
| SEER2 | 15.2 |
| EER2 | 11.0 |
| HSPF2 | 7.8 |
Source: ENERGY STAR Heat Pump Key Product Criteria
A high seasonal rating is useful, but it does not tell you everything about cold-weather performance or whether the system is correctly sized for your house.
Do Air-Source Heat Pumps Work in Cold Weather?
Yes, but model selection matters.
Modern cold-climate air-source heat pumps can continue providing useful heating well below freezing.
ENERGY STAR's current Cold Climate designation requires a qualifying unit to achieve a COP of at least 1.75 at 5°F and maintain at least 70% of its 47°F heating capacity at 5°F.
Ducted cold-climate split systems also need at least 8.1 HSPF2, while non-ducted split systems need at least 8.5 HSPF2.
Source: ENERGY STAR Cold Climate Criteria
The certification is a useful screening tool, but northern installations still need a contractor to compare the home's heat loss with the specific model's output at the local winter design temperature.
Do Air-Source Heat Pumps Need Backup Heat?
Not always.
Backup heat is a design decision, not a universal requirement.
Depending on the house and climate, backup can be:
- Electric resistance heat
- An existing gas furnace
- A new dual-fuel furnace
- Another heating appliance
- No separate backup at all
The correct choice depends on the selected heat pump's low-temperature capacity, the home's heating load, utility rates, electrical service, and the owner's tolerance for redundancy.
Do not let a contractor size backup heat without first showing the primary heat pump's actual low-temperature output.
What Are the Advantages of an Air-Source Heat Pump?
One system can heat and cool
A heat pump can replace separate air-conditioning and heating functions in a single system.
It works with different distribution systems
Air-source technology can be used with central ducts or ductless indoor units.
Modern systems can operate across wide capacity ranges
Variable-speed inverter compressors can adjust output as the load changes, helping the system run longer at lower output instead of cycling repeatedly at full capacity.
A DOE-funded heat-pump guide describes variable-speed inverter compressors and staged equipment as ways to match output to changing loads and limit short cycling.
Source: DOE Better Buildings - Decarbonizing Building Thermal Systems
It can be a practical retrofit
Homes replacing central AC, electric resistance heat, propane, or oil often have a straightforward path to an air-source system.
What Are the Disadvantages?
Performance depends on outdoor conditions
Heating capacity and efficiency change as outdoor temperature changes.
That does not make air-source systems unsuitable for cold weather, but it makes low-temperature selection important.
Existing duct problems remain duct problems
A new heat pump does not repair undersized returns, disconnected ducts, excessive leakage, or bad airflow.
Electrical work may be required
A conversion can require new circuits, disconnects, electric backup-heat capacity, or a panel/service upgrade.
Installation quality matters
Refrigerant charge, airflow, drainage, controls, equipment matching, and commissioning all affect the final system.
Air-Source vs. Geothermal Heat Pump
Both move heat, but they use different external heat sources.
| Factor | Air-source | Geothermal |
|---|---|---|
| External heat source/sink | Outdoor air | Ground or groundwater |
| Outdoor equipment | Conventional outdoor unit | Ground-loop system plus indoor equipment |
| Upfront complexity | Lower | Higher |
| Cold-weather exposure | Performance changes with outdoor air | Ground temperature is more stable |
| Retrofit practicality | High for many homes | Site and project dependent |
| Ground excavation/drilling | No | Usually yes |
Geothermal can deliver excellent efficiency, but the ground loop changes the economics and installation scope.
How Much Does an Air-Source Heat Pump Cost?
Whole-home installation price varies with system size, equipment tier, ductwork, electrical work, labor market, and climate requirements.
Do not compare only outdoor-unit prices.
The number that matters is the complete installed system after required building work and available rebates.
Is an Air-Source Heat Pump Right for Your Home?
An air-source heat pump is a strong candidate when:
- You need both heating and cooling.
- Your air conditioner is already due for replacement.
- You use electric resistance, propane, or oil heat.
- You want to add cooling to a home without it.
- You want room-by-room zoning with ductless equipment.
- You live in a cold climate and can select a properly sized cold-climate system.
The wrong way to decide is to ask whether "heat pumps work" in your state.
The right question is whether a specific system, at a specific size, can meet your home's load at local design conditions at an acceptable installed and operating cost.
Compare system types and the best heat pumps before choosing equipment.
Compare Air-Source Heat Pump Quotes
Ask local installers to quote the same home load so you can compare equipment, low-temperature capacity, installation scope, and net cost.
Prepare for installer conversations
Check the design process and compare written scopes, equipment matches, and installed costs.