Heat pump blowing cold air
A heat pump blowing cold air in winter is often doing exactly what it's designed to do. During a defrost cycle it briefly sends cooler air inside, and even normal heat pump air feels cooler than furnace air. Start by ruling out those two, then check the thermostat, the filter and the outdoor unit. If the outdoor unit runs but the air stays cold for a long stretch, the problem may be the reversing valve or refrigerant, and that's a job for an HVAC technician. Heat pump air feels cooler than furnace air even when it's working. Measure it before you worry.
Why a heat pump blows cool air
A heat pump doesn't burn fuel. In heating mode it pulls heat out of the outdoor air and pumps it inside, using a reversing valve to run the same refrigerant loop it uses for cooling in the opposite direction. Because it moves heat rather than making it, the air at the registers is warm but not hot, usually somewhere around 85–95°F.
In cold, damp weather, frost builds up on the outdoor coil. The system clears it by switching briefly into cooling mode, which warms the outdoor coil. While that happens you may feel cooler air indoors and see steam rising from the outdoor unit. Most systems also have backup electric heat, called auxiliary or emergency heat, for very cold weather.
Common causes of cold air
The system briefly runs in cooling mode to melt frost off the outdoor coil.
COOL mode, a low setpoint or the fan set to ON.
Snow, leaves or ice stop it from pulling heat from the air.
The system can't switch into heating or doesn't have enough refrigerant to move heat.
| You notice | Likely cause | Start at |
|---|---|---|
| Steam from outdoor unit, cool air briefly | Normal defrost cycle | Step 1 |
| Air feels lukewarm, not hot | Normal heat pump air temperature | Step 2 |
| Cold air steadily, outdoor unit running | Thermostat in COOL or wrong setting | Step 3 |
| Cool air between cycles | Fan set to ON | Step 4 |
| Weak airflow from vents | Dirty filter | Step 6 |
| Outdoor unit buried in snow or ice | Blocked outdoor coil | Step 7 |
| Indoor fan runs, outdoor unit silent | Tripped breaker or disconnect off | Step 8 |
Let's fix it
- Rule out a defrost cycleGo outside and look at the outdoor unit. If the fan has stopped and you see steam or water dripping off the coil, it's defrosting. That usually lasts a few minutes up to about 15, and the air inside may feel cool until it finishes. If the cold air stops when the steam does, nothing is wrong.
- Measure the air temperatureHold a thermometer in a supply register near the indoor unit for a few minutes while the system is heating. Air in the 85–95°F range is normal for a heat pump, even though it can feel cool on your hand, especially if you're used to a furnace. If it reads close to room temperature or below, keep going.
- Check the thermostat modeMake sure the thermostat is set to HEAT, not COOL or OFF, and that the setpoint is a few degrees above the room temperature. Replace the batteries if the display is dim. On a newly installed thermostat, the reversing valve setting (often labeled O/B) can be set the wrong way, which makes the system cool when you ask for heat; check the installer settings in the manual or have the installer look at it.
- Set the fan to AUTOIf the fan is set to ON, the indoor blower runs all the time, including between heating cycles and during defrost. That moving air feels cool. Switch it to AUTO so the fan only runs while the system is actually heating.
- Use emergency heat only as a stopgapEmergency heat (EM HEAT) shuts off the heat pump and runs only the electric backup strips. It's meant for when the outdoor unit is broken, and it's very expensive to run for long. If the house is getting cold while you wait for a repair, switch to it for comfort, then call a technician. Don't leave it on as the normal setting.
- Replace a dirty filterPull out the filter at the indoor unit or return grille and hold it up to a light. If you can barely see through it, replace it. A clogged filter cuts airflow, which lowers how much heat reaches the rooms and can make the system shut down on its safety controls.
- Clear the outdoor unitTurn the system off at the thermostat. Brush snow and leaves away from the sides and top, and keep at least two feet clear around the unit. If the coil is encased in ice, don't chip at it, which can puncture the coil. Let it melt on its own or pour lukewarm water from a hose over it, then turn the system back on so it can run a defrost cycle. Drain and put away the hose afterward so it doesn't freeze. Also check that roof runoff isn't dripping onto the unit and refreezing.
- Check the outdoor unit's powerIf the indoor fan runs but the outdoor unit is silent, check your panel for a tripped breaker for the heat pump. It's usually a double breaker, and both handles trip together, so push them fully off and then back on. Also check that switch in the box near the outdoor unit is on. If the breaker trips again, leave it off and call a technician.
Watch it done
- Air at the vents reads about 85 to 95 degrees while heating
- The house reaches the set temperature
- Cool air only shows up briefly during defrost
Air still near room temperature? Call a heat pump technician.
If it's still blowing cold
If the outdoor unit is running and isn't iced over but the air at the registers stays near room temperature, the system may be low on refrigerant or the reversing valve may be stuck. Both need a licensed technician.
If the house only goes cold during very cold snaps, the heat pump may be running past what it can supply and the backup heat may not be kicking in. A technician can check the auxiliary heat strips and the thermostat staging.
What a pro typically charges (a rough estimate; prices vary by area): An HVAC service call typically runs $100–$250. Fixing a refrigerant leak and recharging often costs $300–$1,500, a defrost control board $250–$600, and a reversing valve replacement $1,000–$2,500 installed.
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Heat pump cold air questions
Why is my heat pump blowing cold air in winter?
Often it's a defrost cycle, which briefly sends cooler air in while the outdoor coil melts off frost.
How warm should air from a heat pump feel?
Usually around 85–95°F at the register. It feels cooler than furnace air but is still heating.
When should I use emergency heat?
Only when the outdoor unit isn't working and you're waiting for a repair. It's expensive to run.
Is steam coming from my heat pump normal?
Yes, during defrost. Smoke or a burning smell is not, so turn it off and call a technician.
Why does my heat pump blow cool air for a few minutes?
It's probably a defrost cycle, when the unit briefly sends cooler air inside while it melts frost off the outdoor coil. That's normal.