Understanding what is a heat pump and how heat pump systems work
A heat pump is an electric device that transfers thermal energy from one location to another against the natural direction of heat flow. Unlike traditional heating systems that generate heat through combustion or electrical resistance, heat pumps move existing heat energy from one place to another, they don’t create heat themselves.
Here’s a fundamental point many homeowners miss: even cold outside air contains heat energy that can be captured. At our northern Arizona elevations, this becomes critically important to understand.
What heat pumps use to transfer heat: the basics of heating mode and cooling mode
Heat pump systems work by circulating refrigerant through a closed-loop system of coils and components. This refrigerant undergoes phase changes (liquid to gas and back) to absorb and release heat.
In heating mode, the process works as follows:
The liquid refrigerant passes through an expansion valve, causing it to cool significantly.
This cold refrigerant flows through the outdoor unit’s heat exchange surface, where it absorbs heat from the outside air (yes, even cold air contains heat energy).
The refrigerant evaporates as it warms, turning from liquid to gas.
A compressor pressurizes this gas, dramatically increasing its temperature (this is a crucial step, the compression creates the temperature differential that makes the system viable in cold weather).
The hot refrigerant gas flows to the indoor unit, where it transfers heat to your home’s air or water system.
As it releases heat, the refrigerant condenses back into a liquid, and the cycle repeats.
In cooling mode, the process reverses via a component called the reversing valve:
The system extracts heat from inside your home (cooling the indoor space).
The captured heat gets expelled to the outside environment.
The cooling mode functions essentially identical to a traditional air conditioner.
Translation: Your heat pump is essentially an air conditioner that can run backwards. In summer, it pulls heat from your home and dumps it outside. In winter, it extracts heat from outdoor air and moves it inside.
How the indoor unit and air handler support heating and cooling functionality
The indoor components of a heat pump system play a critical role in transferring heat to or from your living space. In most residential systems, this includes:
The indoor unit containing the indoor coil (a heat exchanger)
An air handler with a blower fan
Sometimes a backup heating element
During heating mode, the indoor coil functions as a condenser, releasing heat into your home as the refrigerant changes from gas to liquid. The air handler’s fan then distributes this warm air through your existing ductwork or through dedicated air outlets in ductless systems.
Hmm… that’s probably too technical. Here’s what this means for your home: The indoor unit extracts heat from the refrigerant and the air handler blows this warmth throughout your space. In homes with existing ductwork, we can often use these ducts to distribute the heated or cooled air.
When operating in cooling mode, this same indoor coil becomes an evaporator, absorbing heat from your indoor air as the refrigerant changes from liquid to gas. This cools the air passing over the coil before it’s circulated back into your living spaces.
I’ve noticed that many Northern Arizona homes built in the 1970s-1990s have undersized or poorly designed ventilation systems. This is critical when considering a heat pump installation because proper airflow is essential for efficient heat transfer.
Why a heat pump works differently from a furnace or air conditioner
Understanding the difference between heat pumps and conventional systems helps explain their efficiency advantages:
A gas furnace creates heat through combustion, burning natural gas, propane, or oil to generate thermal energy. Typical efficiency ranges from 80-98%.
An electric resistance heater creates heat by passing electricity through resistive elements, similar to a toaster or space heater. These are essentially 100% efficient at converting electricity to heat, but that doesn’t make them economical.
A conventional air conditioner only provides cooling by extracting heat from indoors and releasing it outside.
A heat pump, on the other hand, doesn’t create heat, it transfers existing heat energy from one place to another. This fundamental difference allows heat pumps to deliver 2-5 times more heating energy than the electrical energy they consume.
Contractor’s Truth: Many HVAC contractors still don’t fully understand heat pump efficiency ratings and may try to sell you on simpler, more familiar systems. I’ve seen numerous cases where propane furnaces were installed in situations where modern cold climate heat pumps would have provided better performance at a fraction of the operating cost.
What I wish I’d known: When I installed my first few heat pumps in Flagstaff 15 years ago, I underestimated the importance of proper defrost cycles at high elevations. Modern units have significantly improved their defrost capabilities, making them much more suitable for our mountain communities than earlier generations.
Types of heat pumps and their use cases
Heat pumps come in several configurations, each with distinct advantages for specific applications. I’ve installed all types across Northern Arizona, and I’ve found that matching the right technology to each home’s situation makes all the difference in performance and owner satisfaction.
Air source heat pumps: most common residential cooling system
Air source heat pumps extract heat from the outside air and transfer it indoors. These are the most widely installed type due to their reasonable installation cost and versatility.
The primary categories include:
Ducted air source heat pumps: These integrate with existing ductwork and replace traditional furnace/AC combinations. They’re ideal for homes already equipped with functional ducts and provide both heating and cooling through a central system.
The outdoor unit looks similar to a traditional air conditioner but contains additional components allowing it to operate in reverse for heating. Inside, the air handler connects to your ductwork, distributing warm or cool air throughout your home.
Ductless mini-split heat pumps: Perfect for homes without existing ductwork or for adding conditioning to specific zones. These systems pair an outdoor unit with one or more indoor units mounted on walls or ceilings.
I recently installed a ductless system in a 1980s cabin in Munds Park where adding ductwork would have been prohibitively expensive. The owners were thrilled with both the performance and the ability to control temperatures in different areas independently.
Real Talk: Air source heat pumps have historically struggled in very cold weather, but modern cold climate heat pumps have overcome many of these limitations. I’ve personally tested units that maintain 80% capacity at 0°F (-18°C) and continue operating (though with reduced efficiency) well below that. For our mountain elevation homes, selecting a proper cold climate rated unit is essential.
Ground source heat pumps: tapping into earth’s stable temperatures
Geothermal heat pump (also called ground source heat pumps) use the constant temperature of the earth as their heat exchange medium instead of fluctuating outdoor air temperatures.
Here’s what makes them unique:
Rather than extracting heat from variable air temperatures, they use the ground’s constant temperature (roughly 55°F/13°C at depth in Northern Arizona).
A closed loop of piping circulates a heat transfer fluid underground where heat is exchanged with the earth.
These systems maintain exceptional efficiency even in extreme weather since ground temperatures remain stable year-round.
They typically offer 30-70% greater efficiency than air source systems, especially in extreme climates.
While the installation cost is substantially higher due to excavation or drilling requirements, operating costs are significantly lower. These systems are particularly valuable in our mountain communities where winter temperatures regularly drop below 0°F (-18°C).
What I wish I’d known: When I installed my first geothermal system near Flagstaff, I underestimated the excavation challenges in our rocky soil. Proper site assessment is crucial, horizontal loops need substantial land area, while vertical loops require specialized drilling equipment that adds to the cost.
Water source heat pumps and their niche applications
Water source heat pumps extract heat energy from bodies of water like lakes, ponds, or wells. While less common in residential applications, they can be highly effective in specific situations.
These systems:
Use water as their heat exchange medium
Require access to a suitable water source
Can achieve excellent efficiency when properly implemented
Work well in moderate climates but may need supplemental heating in very cold weather
In Northern Arizona, water source applications are limited, though I’ve worked on several successful installations utilizing deep wells. These systems require careful design to prevent freezing issues during our cold winters.
One particularly successful installation I worked on used a combination approach, a water source heat pump drawing from a well, backed up by a small propane furnace as a dual fuel system for extreme cold snaps. This provided excellent efficiency most of the winter while ensuring reliability during the coldest periods.
Advantages and challenges of installing a heat pump
Before we jump into advantages and challenges, understand this: what works perfectly in Phoenix might struggle in Kachina Village. At our 6,800-7,000 foot elevations, heat pumps face different challenges than in valley installations. That said, modern systems have made remarkable advances in high-elevation performance.
Energy savings and climate benefits of switching to a heat pump
Heat pumps offer significant advantages over traditional heating systems, particularly about energy efficiency and environmental impact:
Superior energy efficiency: Rather than creating heat, heat pumps transfer existing heat energy, delivering 200-500% efficiency compared to the 80-98% of gas furnaces or 100% of electric resistance heating. This means that for every unit of electricity consumed, 2-5 units of heat energy are provided to your home.
I’ve analyzed utility bills before and after installations in dozens of Northern Arizona homes, and typical energy cost reductions range from 25-50% compared to propane systems.
Reduced carbon footprint: By using electricity more efficiently and eliminating onsite combustion, heat pumps significantly reduce greenhouse gas emissions. As our electrical grid incorporates more renewable sources, this advantage grows even stronger.
Dual functionality: Heat pumps provide both heating and cooling through a single system, eliminating the need for separate furnace and air conditioner installations.
Improved home comfort: Modern heat pumps deliver more consistent temperatures with fewer temperature swings than traditional systems. They also provide excellent humidity control during our monsoon season.
Safety benefits: By eliminating combustion, heat pumps remove risks associated with carbon monoxide and gas leaks.
Customer Spotlight: A retired couple in Mountainaire replaced their aging propane furnace and window AC units with a ducted heat pump system last year. They reported not only lower utility bills but also significantly improved comfort, particularly appreciating the elimination of cold spots that had plagued their 1970s home.
Performance concerns in extreme cold and installation constraints
While heat pumps offer impressive benefits, they do face several challenges, particularly in our mountain climate:
Cold weather performance limitations: Standard air source heat pumps lose efficiency as temperatures drop. Below about 35°F, conventional units begin struggling, and below 0°F, many cannot operate effectively without supplemental heating.
This is why I exclusively recommend cold climate heat pumps for our Northern Arizona installations. These specialized units maintain good efficiency down to much lower temperatures, though they do cost 15-25% more than standard models.
Installation complexity: Proper sizing and installation are critical. I’ve witnessed numerous failed installations where the contractor applied lowland sizing calculations to our elevation, resulting in undersized systems that couldn’t keep up with demand.
Electrical requirements: Heat pumps typically require 240V service and may necessitate electrical panel upgrades in older homes. This is particularly common in 1970s-1990s cabins with limited electrical capacity.
Retrofit challenges: Installing ductwork in existing homes can be disruptive and expensive, though ductless mini-split options offer an excellent alternative.
Contractor’s Truth: Many HVAC companies that work primarily in Flagstaff or Phoenix aren’t familiar with the specific challenges of installations at our elevation. Always verify that your contractor has substantial experience with mountain installations specifically.
Upfront cost vs. long-term value for homeowners
Heat pump systems typically involve higher initial investment than conventional systems, but often deliver compelling long-term value:
Initial investment: Expect to pay about 20-40% more upfront for a quality heat pump system compared to a traditional furnace/AC combination. At our current rates in Northern Arizona:
Standard ducted heat pump system: $12,000-18,000 installed
Cold climate heat pump system: $14,000-22,000 installed
Ductless mini-split systems: $5,000-8,000 per zone installed
Geothermal systems: $25,000-50,000+ depending on property conditions
Operating cost savings: The higher efficiency translates to reduced monthly energy bills, particularly when replacing propane or electric resistance heating. I typically see 30-50% reductions in heating costs.
Maintenance needs: Heat pumps require similar maintenance to conventional systems, regular filter changes and annual professional service. But, the elimination of combustion components reduces some long-term maintenance concerns.
Longevity and durability: Quality heat pump systems typically last 15-20 years with proper maintenance, comparable to traditional systems.
Available incentives: Federal tax credits currently cover 30% of installation costs for qualifying heat pump systems (up to certain limits). Local utility incentives may also apply.
Real Talk: For most Northern Arizona homeowners transitioning from propane heating, the payback period for a cold climate heat pump runs 5-8 years. Those replacing older electric heating often see payback in just 3-5 years.
What I wish I’d known: For my own home in a similar climate, I initially balked at the price difference between standard and cold climate models. After experiencing firsthand how standard units struggle during January cold snaps, I replaced it with a cold climate model. The extra $2,500 would have been worth it from the start.
Overlooked facts, misconceptions, and customer mistakes
After installing hundreds of systems across Northern Arizona’s high-elevation communities, I’ve noticed certain misunderstandings repeatedly cause problems for homeowners. Let’s clear these up to help you avoid costly mistakes.
Why heat pumps use electricity more efficiently than conventional systems
One of the most significant yet least understood advantages of heat pumps is their remarkable efficiency in converting electricity to usable heat:
The physics advantage: Traditional electric heating (baseboards, space heaters) converts electricity directly to heat at essentially 100% efficiency, one unit of electrical energy becomes one unit of heat energy. But, heat pumps leverage the physics of heat transfer to deliver multiple units of heat energy for each unit of electricity consumed.
Understanding the coefficient of performance (COP): Heat pumps are rated with a COP that indicates their efficiency. A COP of 3.0 means the system delivers three units of heat for each unit of electricity consumed, effectively 300% efficiency.
In our Northern Arizona climate, modern cold climate heat pumps maintain COPs between 1.5-3.0 even at 0°F (-18°C), and higher at milder temperatures.
Real-world impact: This efficiency difference translates directly to your utility bill. A home requiring 50,000 BTUs of heating might consume about 15 kWh using a heat pump versus 15-20 kWh with a standard electric heating system.
Translation: Instead of creating heat (which is inherently limited in efficiency), heat pumps move existing heat from one place to another, a process that can deliver multiple units of heat energy for each unit of electricity consumed.
What I wish I’d known: When I first started working with heat pumps, I struggled to explain their efficiency advantage to customers. Now I use this analogy: “Traditional electric heating is like carrying buckets of water uphill, you can only deliver as much water as you can carry. A heat pump is like using the same energy to power a pump that moves many times more water with the same effort.”
Misunderstanding how cooling mode affects indoor comfort
Many homeowners, particularly those transitioning from evaporative coolers or window units, misunderstand how heat pump cooling systems affect indoor comfort:
“It blows cold air”: Unlike traditional air conditioners that might blow very cold air (40-45°F/4-7°C) for short periods, properly sized heat pumps typically deliver more moderate temperature air (55-60°F/13-15°C) for longer periods. This creates more consistent comfort but can be misinterpreted as “not cold enough.”
Humidity control misunderstandings: Heat pumps excel at managing indoor humidity, which is crucial during our monsoon season. But, oversized systems short-cycle and fail to dehumidify properly, leaving homes feeling clammy even though adequate cooling.
Fan operation confusion: Modern ECM motors in heat pump air handlers often run at lower speeds for longer periods, improving efficiency and comfort. Some homeowners mistakenly interpret this continuous operation as wasting energy, when it’s actually optimizing performance.
Contractor’s Truth: I’ve seen numerous cases where homeowners insisted on larger systems than recommended, believing “bigger is better.” Within months, they experience uncomfortable temperature swings, humidity issues, and higher than necessary energy bills. Proper sizing is critical to both comfort and efficiency.
Ignoring the impact of poor sizing or incorrect air handler pairing
The most common technical mistake I encounter in our mountain communities involves improper system sizing and component matching:
Elevation adjustments: At 6,800+ feet, air is approximately 20% less dense than at sea level. This significantly affects heat pump capacity and performance, requiring proper derating of equipment specifications. Many contractors simply use the same calculations they would in Phoenix, resulting in substantial underperformance.
Cold climate considerations: Standard heat pumps are typically rated at 47°F (8°C). Their capacity drops substantially at the sub-zero temperatures we regularly experience. Cold climate models maintain much better performance at low temperatures but must be properly sized for these conditions.
Mismatched components: Heat pump efficiency depends on properly matched indoor and outdoor components. I’ve encountered numerous “hybrid” installations where components were mismatched, severely compromising system performance.
Inadequate ductwork: Existing ductwork designed for traditional furnaces often cannot accommodate the airflow requirements of heat pump systems. This creates noise, efficiency losses, and comfort problems.
Real Talk: I recently helped a homeowner in Kachina Village who had a new heat pump installed by a local company that rarely works at our elevation. Their system was sized using standard calculations, resulting in a unit that couldn’t maintain temperature when it dropped below 20°F. The contractor had installed a unit approximately 1.5 tons smaller than what the home actually needed at our elevation and climate.
Before we jump into the final section, remember this: your heat pump decision should be based on your specific home’s needs, our unique mountain climate conditions, and professional guidance from someone experienced with high-elevation installations.
FAQ
After hundreds of consultations with Northern Arizona homeowners, I’ve compiled answers to the most common questions about heat pumps for our mountain communities. These address the specific concerns I hear most frequently from residents in Kachina Village, Mountainaire, Munds Park, and surrounding areas.
What is the downside of a heat pump?
Heat pumps do have several potential drawbacks that should be considered, particularly in our high-elevation climate:
Higher upfront cost: Quality cold climate heat pumps typically cost 15-40% more to purchase and install than conventional heating and cooling systems, though operational savings often offset this over time.
Performance challenges in extreme cold: Standard heat pumps lose efficiency and capacity as temperatures drop below freezing. While modern cold climate models perform much better, they still experience some reduction in efficiency at the extreme temperatures we occasionally face.
Potential need for backup heat: In areas where temperatures regularly fall below -15°F (-26°C), a supplemental heating system might be advisable. This could be integrated electric resistance heaters or a dual fuel system with a propane furnace backup.
Installation complexity: Proper installation requires specialized knowledge of refrigerant handling, electrical requirements, and system sizing, particularly at our elevation. Finding qualified installers with mountain experience can be challenging.
Electrical requirements: Heat pumps typically require 240V electrical service and adequate amperage. Older mountain homes often need electrical panel upgrades, adding to installation costs.
Is a heat pump the same as a furnace?
No, a heat pump differs fundamentally from a furnace in how it provides heating:
Heat generation vs. heat transfer: A furnace creates heat through combustion (burning natural gas, propane, or oil) or through electrical resistance. In contrast, a heat pump transfers existing heat from one place to another rather than generating heat.
Energy source differences: Furnaces typically use combustible fuels or electrical resistance to create heat. Heat pumps use electricity to power the components that move heat, but don’t convert electricity directly into heat.
Dual functionality: Furnaces provide heating only, while heat pumps deliver both heating and cooling through the same equipment.
Efficiency comparison: Gas furnaces typically operate at 80-98% efficiency, meaning they convert that percentage of fuel energy into usable heat. Heat pumps often deliver 200-400% effective efficiency (COP of 2-4) in moderate conditions.
Temperature of delivered air: Furnaces typically deliver air at 120-140°F (49-60°C), while heat pumps usually deliver air at 90-110°F (32-43°C). This warmer but not hot air is sometimes mistaken for inadequate heating by those accustomed to furnaces.
What is a heat pump in simple terms?
In its simplest form, a heat pump is a device that moves heat from one place to another using a small amount of energy. Think of it as a heat transporter rather than a heat generator.
Here’s a straightforward explanation:
Refrigerator analogy: A heat pump works on the same principle as a refrigerator, but with a reversible function. A refrigerator removes heat from its internal space and releases it into your kitchen. A heat pump can move heat from outdoor air into your home (heating mode) or remove heat from inside your home and release it outdoors (cooling mode).
Winter operation: Even when it feels cold outside, air still contains heat energy. A heat pump extracts this heat, concentrates it through compression, and delivers it to your home.
Summer operation: In warm weather, the heat pump reverses, working exactly like an air conditioner to remove heat from indoor air and release it outside.
Translation: Instead of burning fuel to create warmth, a heat pump captures existing heat from outside and moves it inside during winter. In summer, it removes heat from inside your home and dumps it outside, just like an air conditioner (because it is one).
How does a heat pump work in winter?
The winter operation of a heat pump often confuses homeowners, particularly in cold climates like ours. Here’s how it functions when temperatures drop:
Extracting heat from cold air: Even at 0°F (-18°C), outside air still contains heat energy that can be captured. The heat pump’s outdoor coil acts as an evaporator, containing cold liquid refrigerant that absorbs this heat energy.
Compression raises temperature: After absorbing heat, the refrigerant vapor is compressed, which dramatically increases its temperature, much like how a bicycle pump gets hot when you compress air.
Indoor heat delivery: The hot, high-pressure refrigerant travels to the indoor coil where it releases heat into your home’s air before returning to the outdoor unit to repeat the cycle.
Defrost cycles: In cold, humid conditions, frost can form on the outdoor coil. Periodic defrost cycles temporarily reverse operation to melt this frost, briefly interrupting heating.
Supplemental heating: Most cold climate heat pumps include backup electric resistance heating elements that activate automatically during extreme cold or defrost cycles to maintain comfort.
Contractor’s Truth: Standard heat pumps struggle in Northern Arizona winters. I exclusively recommend cold climate models rated for operation down to -15°F (-26°C) or lower for our mountain communities. These specialized units maintain much better capacity and efficiency in our winter conditions, though they do cost more initially.