Heating Efficiency: Can Through-the-Wall Units Handle Winter?
There’s a myth floating around—one I’ve been hearing for years—that through-the-wall heat pumps can’t handle winter. Homeowners repeat it because they heard it from a neighbor, or from someone who bought the cheapest unit available, or from someone who’s still living in the 1990s HVAC era. Let me be crystal clear, Jake style: heat pumps don’t quit unless you buy junk. The technology has evolved. Modern through-the-wall units can handle moderate and even cold winter conditions, if you choose the right system, size it correctly, understand the efficiency principles, and know what to expect from cold-weather performance curves.
This guide is the myth-buster every homeowner needs. We’re breaking down real technical heating performance—how COP works, how outdoor temperatures affect output, how defrost cycles protect your unit, what backup heat looks like, and which climate zones should absolutely be using a through-the-wall heat pump as primary or supplemental heat.
I’m Jake, and after years of winter installs, test runs, cold-climate troubleshooting, and fixing what bargain units can’t handle, I’m here to lay down the truth. Not guesses. Not internet hearsay. Actual physics, real-world system behavior, and professional HVAC reasoning. Let’s get into it.
1. The Myth: “Heat Pumps Stop Heating When It Gets Cold”
Wrong. Completely wrong.
The myth comes from:
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Outdated heat pump models
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Low-efficiency compressors
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Cheap units are not meant for heating
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Systems with no low-ambient design
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Incorrect sizing
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Poor installation
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Lack of backup heating strategy
Modern through-the-wall heat pumps use advanced technologies:
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Variable-speed compressors
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High-pressure refrigerants
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Intelligent defrost cycles
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Electrically heated drain pans (in some designs)
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Improved coil geometry
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Precision sensor logic
These improvements allow them to heat in outdoor temperatures down into the 30s, 20s, and even teens, depending on model class.
And here’s the truth Jake will repeat throughout this guide:
Buy a unit rated for the climate you live in. The hardware determines the performance—not the myth.
Reference studies similar to modern heat pump evaluations found on Energy Star-style resources confirm these performance ranges.
2. COP Explained — The Real Measure of Heating Efficiency
If you don’t understand COP, you don’t understand heat pump heating. Period.
2.1 What Is COP?
COP = Coefficient of Performance.
It measures how many units of heat your pump delivers for every unit of electricity it consumes.
Example:
COP 3.0 = 3 units of heat delivered for 1 unit of electricity used.
That’s 300% efficiency—something no furnace or space heater can do.
2.2 Why COP Falls in Cold Weather
As outdoor temperature drops:
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There is less heat energy available outside
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The compressor works harder
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Refrigerant pressure drops
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Defrost cycles become more frequent
So COP decreases. That’s normal. Not failure—physics.
2.3 Typical COP Ranges
Based on performance patterns similar to manufacturer data
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47°F outdoor temp: COP 3.0–3.8
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32°F outdoor temp: COP 2.2–3.0
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17°F outdoor temp: COP 1.3–2.0
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5°F outdoor temp: COP 1.0–1.4 (cold-climate models only)
COP remains above electric-resistance efficiency in most conditions.
2.4 The Big Jake Takeaway
If your heat pump stops heating efficiently in the 40s or 30s, it’s because you bought a cheap unit, not a proper heating-rated model.
3. Outdoor Temperature Performance Chart (Jake’s Simplified Version)
The following chart represents typical heating output behavior based on standard and cold-climate through-the-wall units. Values represent approximate percentages of rated heating output relative to outdoor temperature.
| Outdoor Temperature | Standard Through-the-Wall Unit | Cold-Climate Through-the-Wall Unit |
|---|---|---|
| 50°F | 100% output | 100% output |
| 40°F | 95% output | 100% output |
| 32°F | 85% output | 95% output |
| 25°F | 70% output | 90% output |
| 17°F | 55% output | 80% output |
| 10°F | 40% output | 70% output |
| 0°F | Not recommended | 55–65% output |
Performance curves similar to those tested on show nearly identical patterns.
The chart proves a simple truth:
Choose the right category of unit, and winter is not a problem.
4. Defrost Logic — The Hidden Powerhouse of Cold-Climate Performance
Homeowners panic when they see frost or steam coming from their heat pump. Jake does not panic. He knows what’s going on: the defrost cycle, a normal and essential mode of operation.
4.1 Why Frost Happens
In winter, coils get below freezing. Moisture in the air condenses and freezes on the coil. Frost reduces:
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Airflow
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Heat absorption
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Efficiency
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Heating output
4.2 How Defrost Mode Works
The heat pump briefly reverses its refrigerant cycle:
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Coil warms
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Frost melts
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Drain pan releases water
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System returns to heating mode
This takes 3–10 minutes typically.
4.3 Intelligent Logic
Modern systems activate defrost based on:
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Coil temperature
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Outdoor temperature
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Run time
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Humidity levels
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Sensor comparisons
Nothing about defrost indicates a failing unit.
4.4 Jake’s Rule
If your heat pump never goes into defrost, that’s the real problem, not the frost.
4.5 Steam Is Normal
Homeowners often think their unit is “smoking.”
Nope—it's steam from evaporating frost.
5. Backup Heat Options: When You Need Them & What Works Best
Through-the-wall heat pumps heat well—but there are limits. Backup heat isn’t a sign of weakness. It’s smart system design.
Jake approves the following backup heaters:
5.1 Electric Baseboard Heat (Most Common Add-On)
Works best for:
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Bedrooms
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Small apartments
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Older homes
Pros:
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Instant heat
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Simple installation
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Cheap to purchase
Cons:
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Least efficient
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Should run only below heat pump limits
5.2 Ceramic or Infrared Space Heaters (Temporary Backup)
Use only as:
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Occasional support
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Emergency heat
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Supplemental heating
Never rely on these as primary.
5.3 Wall-Mounted Electric Heater
Best for:
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Medium-size rooms
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Supplemental heat zones
Provides steady heating without overloading circuits.
5.4 Smart Thermostat Logic for Hybrid Heating
Some through-the-wall heat pump brands offer compatibility with:
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Dual control logic
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Temperature setpoints
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Auxiliary triggers
Example logic:
“Use heat pump above 25°F. Trigger backup heat below 25°F.”
5.5 Oil-Filled Radiator Heaters
Jake’s favorite backup option because:
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They provide quiet, steady heat
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They do not spike the electrical load
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They distribute radiant warmth evenly
6. Cold-Climate Use Cases: Where Through-the-Wall Units Actually Work
Homeowners in colder regions are often surprised to learn that through-the-wall heat pumps work extremely well in:
6.1 Midwestern Winters
Temperatures in the 20s–30s are ideal for modern wall heat pumps.
Use cases:
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Bedrooms
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Studios
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Living rooms
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Add-on spaces
A supplemental heater only kicks in under 15–20°F.
6.2 Northeast States
Through-the-wall units perform reliably in:
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Maryland
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New Jersey
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Pennsylvania
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Long Island
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Coastal Connecticut
Heat pumps deliver primary heat in most of these areas.
6.3 Pacific Northwest
The region is practically made for heat pumps.
Winter temperatures:
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30s–40s consistently
Heat pumps dominate here.
6.4 Coastal New England
Mild coastal regions like:
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Cape Cod
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Rhode Island coast
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Southern Massachusetts
…are perfect for through-the-wall heating.
Manufacturer Defrost Logic Example
6.5 Rocky Mountain Regions at Moderate Elevations
Homes at 3,000–5,500 ft often experience:
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Cold nights
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Mild days
Heat pumps shine in mixed-weather environments.
6.6 Southern Canada (Border Regions)
Carefully selected cold-climate units handle:
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Ontario lake regions
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British Columbia
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Southern Quebec
These areas require supplemental heating only during extreme cold spells.
Information similar to the Cold-Climate Heat Pump Study echoes these results.
7. What Determines Whether Your Heat Pump Can Handle Winter
Jake will break it down simply: winter performance comes down to five things.
7.1 BTU Size
If you undersize your system, it will fail in any climate.
7.2 Low-Ambient Rating
Units rated for:
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5°F
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0°F
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–5°F
…are available.
Cheap units often struggle below 35°F because they’re not designed for winter.
7.3 Quality of Installation
Bad installation kills heating performance.
7.4 Airflow and Placement
Blocked airflow = weaker heating output.
7.5 Defrost System Quality
Cheap units freeze. Good units defrost on schedule.
8. When a Through-the-Wall Heat Pump Should NOT Be Primary Heating
Jake tells the truth—even when it’s not what you want to hear.
Heat pumps should NOT be primary heat in:
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Regions where winter temps routinely fall below 0°F
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Homes with extreme drafts
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Historic homes lacking insulation
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Rooms with poor airflow
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Garages are uninsulated in sub-zero climates
Backup heating is absolutely required in these environments.
EPA Heating Efficiency Resource
9. Comparing Heat Pumps to Space Heaters & Furnaces in Winter
Let’s bust even more myths.
9.1 Heat Pump vs Space Heater
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Heat pumps: 200–350% efficient
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Space heaters: 100% efficient
Winner: Heat pump
9.2 Heat Pump vs Gas Furnace
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Furnace: great for extreme cold
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Heat pump: better for mild-to-cold climates
Winner: depends on the climate
But heat pumps win for efficiency at 25–50°F.
9.3 Heat Pump vs Electric Baseboard
Baseboard heaters are 100% efficient but expensive to run. Heat pumps cost far less per heating hour.
Winner: Heat pump
Conclusion — Heat Pumps Don’t Quit Unless You Buy Junk
The myth that through-the-wall heat pumps “can’t handle winter” is outdated, inaccurate, and based on ancient equipment. Modern heat pumps deliver real heating in temperatures ranging from the 40s all the way down to the teens—sometimes even single digits if you buy a cold-climate model. Understanding COP, performance curves, and defrost cycles is the key to setting realistic expectations. Combine that with the right BTU size and optional backup heat, and your through-the-wall unit becomes a powerful winter performer.
Heat pumps don’t quit unless you buy junk. And Jake never recommends junk.
In the next blog, you will learn about Energy Use Breakdown: How Much Does a Through-the-Wall Heat Pump Cost to Run?
