The Short Answer
Yes, They Work
Modern heat pumps are significantly more capable than the systems from 10 or 15 years ago. But understanding why requires knowing a little about how they work and what separates a good installation from a mediocre one.
Heat pumps have become standard for heating and cooling in Virginia because they’re efficient in our climate. But there’s a persistent question that comes up, especially when temperatures drop into the teens: can a heat pump actually keep up?
The technology has improved dramatically. Current systems handle Virginia winters without issue. But the equipment is only part of the story. How it’s sized, what air handler it’s paired with, and how well the home is built all affect performance.
This article explains how heat pumps work, what’s changed in recent years, and what to look for when evaluating a builder’s HVAC specifications.
The Basics
How Heat Pumps Actually Work
A furnace generates heat by burning fuel. A heat pump does something different: it moves heat from one place to another.
Even when it’s cold outside, there’s heat energy in the air. A heat pump extracts that heat and moves it inside. In summer, the process reverses, and the system moves heat from inside your home to the outside. One system, two functions.
This is why heat pumps are so efficient. Moving heat takes less energy than creating it. A well-functioning heat pump can deliver two to three times more heat energy than the electricity it consumes. No furnace can match that efficiency.
The catch is that as outdoor temperatures drop, there’s less heat available to extract, and the system has to work harder. This is where older heat pumps struggled, and it’s where modern technology has made the biggest improvements.
Efficiency Advantage
Heat pumps move heat rather than generate it. At moderate temperatures, they can deliver 3-4 units of heat energy for every unit of electricity consumed. Even in cold weather, modern systems maintain efficiency advantages over electric resistance heating.
Technology Improvements
What’s Changed
Heat pumps have been around for decades, but the early systems had real limitations in cold weather. Two technologies changed everything.
Older units used single-stage compressors that ran at one speed: full blast. When the thermostat called for heat, the system turned on at 100% capacity. When the temperature was satisfied, it shut off. This constant cycling was inefficient and created noticeable temperature swings in the home.
More importantly, those older systems lost capacity as temperatures dropped. A heat pump rated to heat your home at 47 degrees might struggle to keep up at 25 degrees. Below that, many systems couldn’t maintain comfortable temperatures at all without backup heat running constantly.
This is where the reputation came from. People who lived through winters with those older systems remember the heat running nonstop, the house never quite getting warm, and electric bills that went through the roof when the backup heat kicked in.
Variable-Speed Compressors
Instead of running at full blast or not at all, variable-speed systems adjust output to match what the home actually needs. Think of it like cruise control instead of repeatedly flooring the gas pedal and then coasting.
Improved Cold-Weather Performance
Modern refrigerants and compressor designs allow systems to extract heat at much lower temperatures. Cold-climate heat pumps can operate effectively down to -15 degrees or colder.
Consistent Comfort
Variable-speed systems hold the temperature within a degree or two of your thermostat setting. They run longer at lower speeds, which means better air circulation and more even temperatures throughout the house.
Better Efficiency
On a mild day, a variable-speed system might run at 40% capacity, maintaining steady temperature without cycling. On a cold night, it ramps up to meet demand without the energy waste of constant on-off cycling.
Backup Systems
What About Auxiliary Heat?
Heat pumps have backup heating elements that can supplement the heat pump when needed. Understanding when auxiliary heat is normal, and when it’s a problem, helps you evaluate system performance.
You might see “AUX” on your thermostat during cold weather. This indicates the backup heating elements (usually electric resistance coils) are running. This is normal in certain situations.
Auxiliary heat typically kicks in when outdoor temperatures drop below a certain point (much lower on modern systems than older ones), when the system is in defrost mode, or when you raise the thermostat several degrees at once and the system needs help catching up quickly.
The key word is “supplement.” On a properly sized modern system, auxiliary heat runs occasionally and briefly. It shouldn’t be running constantly, and it shouldn’t be carrying most of the heating load.
When to Be Concerned
If your thermostat shows AUX heat running frequently even in moderate temperatures (above 35-40 degrees), something is wrong. Either the system is undersized, the thermostat is misconfigured, or there’s a problem with the heat pump itself. Electric resistance heat is much less efficient than heat pump operation. A system that relies heavily on auxiliary heat will have high electric bills.
Beyond the Equipment
What Makes a Good Installation
Not all heat pump installations are equal. The equipment matters, but so does how it’s sized, configured, and integrated with the rest of the home.
Proper sizing is critical. An undersized system won’t keep up on cold days. An oversized system will short-cycle (turn on and off frequently), which wastes energy, creates temperature swings, and doesn’t dehumidify properly in summer. The system should be sized based on a load calculation for your specific home, not rules of thumb.
Variable-speed equipment makes a significant difference in both comfort and efficiency. Single-stage systems are cheaper upfront but cost more to operate and don’t maintain temperatures as consistently. Variable-speed systems run longer at lower speeds, which is more efficient and more comfortable.
The air handler matters too. The air handler is the indoor unit that circulates air through your home. A variable-speed air handler paired with a variable-speed heat pump delivers the best performance. Some builders pair variable-speed heat pumps with single-speed air handlers to save money, which limits the system’s ability to modulate output.
The Building Envelope Connection
A heat pump is only as good as the home it’s heating. A well-sealed, well-insulated home lets the heat pump operate efficiently. A leaky home with poor insulation makes any heating system work harder and costs more to operate. This is why we consider HVAC and building envelope as a single system.
Read more about building envelope performanceEvaluating Builders
Questions to Ask
If you’re planning a custom home, the answers to these questions tell you a lot about whether a builder is thinking about long-term performance or just checking a box.
What efficiency rating does your standard heat pump have?
Look for the SEER2 rating (cooling efficiency) and HSPF2 rating (heating efficiency). Higher numbers mean better efficiency. Current minimum standards require 15 SEER for split systems.
Is the system single-stage, two-stage, or variable-speed?
Variable-speed is the most efficient and comfortable option. Two-stage is a middle ground. Single-stage is the most basic and least efficient.
What about the air handler?
Is it variable-speed to match the heat pump, or single-speed? A variable-speed heat pump paired with a single-speed air handler can’t deliver its full potential.
How do you size the system?
The answer should involve a load calculation based on the home’s design, insulation levels, window specs, and orientation. Rules of thumb like “one ton per 500 square feet” are a red flag.
What We Include
Every Ellis home includes a 15 SEER heat pump with a variable-speed air handler and programmable thermostat. This is our standard specification, not an upgrade. The variable-speed air handler is the key: it allows the system to modulate output based on conditions, maintaining consistent temperatures without the on-off cycling of basic systems. We also include 200-amp electrical service, which provides capacity for the heating system plus any additional loads you might add later.
Common Questions
Frequently Asked Questions
Yes. Modern heat pumps are significantly more capable in cold weather than systems from 10-15 years ago. Cold-climate heat pumps can operate effectively down to -15 degrees or colder. Virginia winters, which rarely drop below the teens, are well within the comfortable operating range of current technology. Our standard 15 SEER systems with variable-speed air handlers handle Virginia winters without issue.
Auxiliary heat is a backup heating element (usually electric resistance coils) that supplements the heat pump when needed. It kicks in when outdoor temperatures drop below a certain point, during defrost cycles, or when you raise the thermostat several degrees at once. On a properly sized modern system, auxiliary heat runs occasionally and briefly, not constantly. If AUX heat runs frequently in moderate temperatures, the system may be undersized or malfunctioning.
A single-stage heat pump runs at one speed: full blast. It cycles on and off repeatedly, creating temperature swings and using more energy during startup. A variable-speed system adjusts its output to match what the home needs, running longer at lower speeds for more consistent temperatures and better efficiency. Variable-speed systems also perform better in cold weather because they can ramp up gradually rather than cycling on and off.
Current federal minimum standards require 14.3 SEER2 for split-system heat pumps. Higher ratings indicate better cooling efficiency. For heating efficiency, look at the HSPF2 rating. Variable-speed systems typically achieve 20-24 SEER2, while single-stage systems range from 14-16 SEER2. Our standard specification is 14.3 SEER2, which meets current efficiency standards while keeping costs reasonable.
A heat pump is only as good as the home it’s heating. A well-sealed, well-insulated home lets the heat pump operate efficiently at lower output levels. A leaky home with poor insulation makes any heating system work harder, run longer, and cost more to operate. The building envelope and HVAC system should be considered together when evaluating a home’s overall performance.
Proper sizing requires a load calculation based on the home’s design, insulation levels, window specifications, orientation, and local climate data. An undersized system won’t keep up on cold days. An oversized system will short-cycle, wasting energy and creating temperature swings. Rules of thumb like “one ton per 500 square feet” don’t account for the variables that affect actual heating and cooling loads.












