Heat pumps are becoming increasingly common in homes across the country, and buyers and homeowners frequently encounter them without having a clear picture of how they work or how they differ from a furnace. Understanding what is a heat pump and how it differs from a furnace helps make sense of inspection findings, performance expectations, and maintenance considerations for this increasingly prevalent system.
What a Heat Pump Is
A heat pump is a system that moves heat rather than generates it. Instead of burning fuel or using electrical resistance to create heat, a heat pump transfers heat from one location to another using a refrigerant cycle — the same basic process used in air conditioning and refrigeration.
In heating mode, a heat pump extracts heat energy from the outdoor air — even in cold temperatures — and transfers it indoors. In cooling mode, the process reverses: the system extracts heat from the indoor air and rejects it outside, functioning identically to a central air conditioner.
This reversibility is the defining characteristic of a heat pump. One system handles both heating and cooling by changing the direction of the refrigerant cycle. A furnace heats only. For more on how a furnace-based forced-air system works by comparison, see [What Is a Forced-Air Heating System and How Does It Work].
How a Heat Pump Works
A heat pump system has two main components: an outdoor unit and an indoor air handler. The outdoor unit contains a compressor, a refrigerant coil, and a fan. The indoor unit contains another coil and a fan to distribute conditioned air through the ductwork.
In heating mode, refrigerant in the outdoor coil absorbs heat from the outdoor air, even when temperatures are cold. The compressor then raises the refrigerant’s temperature further and circulates it to the indoor coil, which releases the heat into the home’s airstream. The air handler distributes the warmed air through the duct system. Ductwork condition affects this distribution just as it does in a furnace system; for more on that relationship, see [How Airflow Affects Heating and Cooling Systems].
In cooling mode, the refrigerant cycle reverses. The indoor coil absorbs heat from the indoor air, the refrigerant carries that heat to the outdoor unit, and the outdoor fan rejects it into the outside air.
A key efficiency concept: because a heat pump moves heat rather than generating it, it can deliver more energy as heat than it consumes as electricity — often two to three times more, depending on conditions. This is why manufacturers express heat pump efficiency as a coefficient of performance rather than a simple fuel-to-heat ratio.
How Heat Pumps Differ From Furnaces
Fuel source and heat generation. A furnace generates heat by burning fuel — natural gas, propane, or oil — or by using electric resistance elements. A heat pump does not generate heat in this way. It moves heat using refrigerant and a compressor powered by electricity.
Cold weather performance. Furnaces maintain consistent output regardless of outdoor temperature. Heat pumps become less efficient as outdoor temperatures drop, because there is less heat energy available in colder air to extract. Most air-source heat pumps include a supplemental heat source — electric resistance strips or a gas furnace in a dual-fuel system — that activates when temperatures fall below the heat pump’s efficient operating range.
Dual function. A furnace heats only. A heat pump heats and cools using the same equipment. Homes with heat pumps typically do not need a separate central air conditioner.
Appearance and components. From the outside, a heat pump looks nearly identical to a central air conditioner. The outdoor unit is the same type of boxy condenser unit. The difference is in the internal refrigerant circuit and the controls. A system that appears to underperform may have nothing to do with the heat pump itself; for context on diagnosing that distinction, see [HVAC Systems That Work but Don’t Perform].
What Inspectors Evaluate
Inspectors evaluate heat pumps using the same general approach as other HVAC systems, with a few specific considerations.
System operation in available mode. On a warm day, inspectors test the cooling mode. On a cold day, the heating mode. Because heat pumps switch modes, inspectors note which mode they tested and the conditions at the time.
Defrost cycle evidence. Heat pumps in heating mode periodically enter a defrost cycle to clear ice that can form on the outdoor coil in cold, humid conditions. Inspectors may note evidence of proper defrost operation — or of a system that has not been defrosting — during a cold-weather inspection.
Supplemental heat source. If a supplemental heating system — electric strips or gas furnace — is present, the inspector notes its configuration and whether it appears appropriately integrated.
Outdoor unit condition. Inspectors examine the outdoor unit for physical damage, debris accumulation, proper clearances, and electrical connections. The unit should be level on its mounting pad and have adequate clearance from vegetation and other obstructions.
Overall HVAC condition. Age, visible condition, and system performance observations apply to heat pumps as they do to furnace-based systems.
Common Misunderstandings
“A heat pump can’t heat well in cold weather.”
Modern heat pumps operate efficiently at much lower temperatures than older units could manage. Cold-climate heat pumps can extract usable heat from outdoor air well below freezing. Supplemental heat sources handle conditions at temperature extremes. The technology has advanced significantly.
“The outdoor unit is just for air conditioning.”
In a heat pump system, the outdoor unit participates in both heating and cooling. Buyers familiar with furnace-plus-air-conditioner systems sometimes misidentify a heat pump’s outdoor unit as an AC unit and do not realize the home has heat pump heating as well.
“Heat pumps are new and unproven.”
Heat pumps have been in widespread residential use for decades, particularly in moderate climates. Their increasing adoption in colder climates is driven by improvements in technology and efficiency, not novelty. They are a well-established system type.
Educational Takeaway
A heat pump is a system that moves heat rather than creating it, and it provides both heating and cooling through a single reversible refrigerant cycle. The distinction from a furnace matters for understanding performance expectations in cold weather, operating costs, and what inspectors are evaluating when they assess the system. As heat pumps become more common in homes across all climate regions, understanding how they work makes it easier to evaluate what an inspection report is communicating about them.
Educational Disclaimer
Inspector Howe provides general educational information to help you better understand your home. This content is not a professional inspection, certification, or compliance determination. Always consult a qualified professional for assessment of your specific property.
