Heat Pump Not Heating in Cold Weather: Causes and Fixes

It’s 30 degrees outside and your heat pump is blowing cold air—what’s going on?

You were told a heat pump could heat your home. But now it’s cold outside, the system is running, and the air coming from your vents feels lukewarm at best. You’re wondering if someone sold you the wrong system or if heat pumps just don’t work in winter. At H&H Heating and Air Conditioning, we hear this concern every winter. The truth is, heat pumps work differently than furnaces, and understanding how they operate can save you a lot of worry—and help you know when something actually is wrong.

How Heat Pumps Heat Your Home

Unlike a furnace that creates heat by burning fuel, a heat pump extracts heat from outdoor air and moves it inside—even when it’s cold outside. Yes, cold air still contains heat energy. The refrigerant in your heat pump absorbs that heat, compresses it to raise the temperature, then releases it inside your home.

This makes heat pumps incredibly efficient in moderate climates. But it also means they behave differently than furnaces.

Why Heat Pump Air Feels Different

Here’s something that surprises many homeowners: heat pumps typically blow air at 90-100°F, while furnaces blow air at 120-140°F. Since your body temperature is around 98.6°F, heat pump air can feel lukewarm even though it’s actively heating your home.

This isn’t a malfunction—it’s normal operation. Your home still reaches the set temperature, just more gradually. Heat pumps run longer cycles to deliver the same amount of heat at a lower temperature.

How to check if it’s working: Watch your thermostat. If your home gradually reaches the set temperature and the system shuts off, your heat pump is doing its job.

Normal Cold Weather Behaviors

Several heat pump behaviors seem like problems but are actually normal:

Longer run times: Heat pumps run more in cold weather to maintain temperature. This is efficient operation, not a sign of trouble.

Defrost cycle: When frost builds on the outdoor coil, your system temporarily reverses to melt it. During defrost, you may feel cool air from your vents for a few minutes. The outdoor unit may steam (that’s ice melting). A normal defrost cycle lasts 5-15 minutes and shouldn’t happen more often than every 30-35 minutes.

Backup heat activating: When temperatures drop below about 35-40°F, auxiliary heat (usually electric strips) kicks in automatically to supplement the heat pump. This is normal and keeps your home comfortable.

Not sure if what you’re experiencing is normal? Call us—we’re happy to help you understand your system.

When There’s Actually a Problem

Call for service if you notice:

• Air from vents is truly cold, not just lukewarm
• Home never reaches thermostat set temperature despite continuous running
• Outdoor unit is covered in solid ice (light frost is normal, a block of ice is not)
• Backup heat isn’t coming on when it should
• System runs constantly but house stays cold
• Unusually high energy bills

Common Causes of Poor Cold Weather Performance

Dirty air filter: A clogged filter restricts airflow, reducing efficiency and potentially triggering safety shutdowns. Check and replace monthly in winter.

Frozen outdoor unit: Light frost is normal. Solid ice covering the coils means the defrost cycle isn’t working—this requires professional repair.

Low refrigerant: A leak reduces the system’s ability to transfer heat. Signs include poor heating, ice buildup, and hissing sounds.

Faulty reversing valve: This valve switches the system between heating and cooling modes. If it’s stuck in cooling mode, you’ll get cold air when you need heat.

Outdoor unit blocked: Snow, debris, or ice obstructing airflow prevents proper operation. Keep two feet of clearance around the unit.

Thermostat issues: Verify it’s set to HEAT (not COOL) and the fan is on AUTO (not ON, which blows air constantly even when not heating).

Auxiliary Heat vs. Emergency Heat

These terms confuse many homeowners:

Auxiliary heat kicks in automatically when your heat pump needs help—during very cold weather, defrost cycles, or when you raise the temperature several degrees at once. The heat pump keeps running while aux heat supplements it. This is normal.

Emergency heat is a manual override that bypasses the heat pump entirely and runs only on backup heat. Use it only if your heat pump fails completely—running emergency heat all winter will significantly increase your energy bills.

Important: If your thermostat shows “Aux Heat” constantly even when outdoor temperatures rise, or if the “Emergency Heat” indicator is on but you didn’t turn it on, call for service.

What You Can Do

Check the filter: A dirty filter is the most common cause of heating problems.

Clear the outdoor unit: Remove snow, ice, and debris. Maintain two feet of clearance on all sides. Never cover the unit—it needs airflow.

Verify thermostat settings: Confirm it’s set to HEAT, not COOL or emergency heat.

Don’t chip ice off the unit: You can damage the coils. If it’s frozen solid, call a professional.

Avoid big temperature jumps: Raising the thermostat several degrees at once triggers aux heat. Adjust 1-2 degrees at a time.

When to Call a Professional

Call for service if:

• Outdoor unit is covered in solid ice that doesn’t melt
• Defrost cycle runs constantly or doesn’t work at all
• No heat despite the system running
• Backup heat never activates
• You hear unusual noises or smell something burning
• Refrigerant leak suspected (ice, hissing, poor performance)

Keep Your Heat Pump Running Well

Heat pumps are designed to work in cold weather—but they work differently than furnaces. Some behaviors that seem like problems are normal operation. But if your home isn’t getting warm, your outdoor unit is a block of ice, or your backup heat isn’t working, something needs attention.

At H&H Heating and Air Conditioning, we’ll help you figure out what’s normal and what needs repair. Our technicians will give you the honest answer—not push a replacement you don’t need.

Heat pump struggling this winter? Call H&H for honest diagnosis.

Frequently Asked Questions