Quick answer: Often it’s normal: heat pump air is warm but not furnace-hot, and a defrost cycle can blow cooler air for a few minutes. If it stays cold, check that the thermostat is on Heat, the fan is on Auto, the filter is clean and the breakers are on. Air that keeps blowing cold usually means a repair, such as a refrigerant leak or a stuck reversing valve.
Is it normal for a heat pump to blow air that feels cool?
Yes, often it is. A gas furnace heats air with a flame, so what comes out of the vents feels hot. A heat pump moves heat from outdoors to indoors and delivers air that’s warmer than your room but noticeably less hot. Hold your hand up to a vent and it can feel lukewarm or even cool, especially on a cold morning when your hand is cold too. If the house is slowly warming up and holding temperature, the heat pump is doing its job.
Heat pumps also run longer, steadier cycles than furnaces. That’s normal, and usually more comfortable than short blasts of very hot air.
Why does my heat pump blow cool air and steam during defrost?
Because it’s melting frost off the outdoor coil. In cold, damp weather, frost builds up on that coil, and to clear it the heat pump briefly switches into reverse. During defrost you may notice:
- The outdoor fan stops while the compressor keeps running.
- Steam or vapor rising from the outdoor unit. That’s melting frost, not smoke.
- A whooshing sound as the system switches into and out of defrost.
- Cooler air from the vents for a few minutes, unless the system brings on heat strips to temper it.
A defrost cycle normally lasts only a few minutes, then normal heating resumes. Light frost on the outdoor unit is expected in winter. A unit that stays wrapped in thick ice after several defrost cycles is not, and it should be checked. Don’t chip or pry ice off the coil; the fins and tubing bend if you look at them wrong.
What should I check before calling for service?
- Thermostat mode. Make sure it’s on Heat, not Cool, and not Auto with a low cooling setpoint.
- Fan setting. If the fan is set to On, it keeps blowing between heating cycles, and that circulating air feels cool. Set it to Auto.
- Setpoint. It needs to be above the current room temperature for heat to run.
- Filter. A clogged filter restricts airflow and can make the system overheat or shut down. Replace or clean it.
- Breakers. Heat pump systems usually have separate breakers for the outdoor unit and the indoor air handler or heat strips. If one has tripped, the system may run with only part of its heat.
- Outdoor unit. Clear away leaves, mulch or anything blocking airflow around it.
If a breaker trips again after you reset it, leave it off and call for service. Resetting it over and over isn’t a fix.
What problems make a heat pump blow cold air?
When the checks above don’t solve it and the air stays cold, these are the causes we find most often:
- Low refrigerant from a leak. The system can’t move enough heat indoors. Topping it off without finding the leak is only a temporary fix.
- A stuck reversing valve. This valve switches the heat pump between heating and cooling. If it sticks in the cooling position, you get cool air in heat mode.
- A defrost control or sensor fault. The unit may stay in defrost too long, or never defrost and ice over.
- A failed compressor or outdoor fan motor. The outdoor unit may hum, click or not start at all.
- Heat strip problems. A failed strip, relay or sequencer means no backup heat during freezes and defrost.
- Thermostat or wiring issues. Especially right after a new thermostat goes in.
- Leaky or disconnected attic ductwork. In many Austin homes the ducts run through an unconditioned attic. A torn or disconnected duct can dump warm air into the attic and pull cold air in, so you end up heating the attic very nicely. See Understanding Your Home’s Duct System.
If the heat pump isn’t heating at all and you’re waiting on a repair, switching the thermostat to emergency heat can keep the house warm on backup heat in the meantime.
Should I repair or replace a heat pump that blows cold air?
Many cold-air problems are straightforward repairs. It becomes a bigger decision when the system is older, has a major failure like a compressor, uses R-22 refrigerant (production ended in 2020), or has needed several repairs in a short time. Our guide Repair or Replace? Deciding What’s Best for Your HVAC System covers how to weigh it, and our heat pump services page shows what a replacement involves.
Thinking about a new system? You can build your system online to compare heat pump, dual fuel and gas furnace options for your home and see an estimate in a few minutes. Our local team reviews every build and confirms the details at an in-home visit.
Frequently asked questions
Why does my heater blow cold air, then warm air?
That’s often a defrost cycle, or the start of a heating cycle before the indoor coil warms up. If it’s brief and the house stays warm, it’s usually normal.
Why is steam coming from my outdoor unit?
It’s frost melting off the outdoor coil during defrost, and it usually stops within a few minutes. Smoke, a burning smell or loud grinding is different and needs service.
How do I know if my reversing valve is bad?
A common sign is cool air in heat mode, or warm air in cooling mode, with the outdoor unit running. Other problems can cause similar symptoms, so a technician needs to test it.
Should I cover my heat pump in winter?
No. The outdoor unit needs airflow to heat and defrost, so keep it clear instead. For freeze tips, see Can a Heat Pump Keep Up With a Texas Freeze?.
The bottom line
A heat pump that feels lukewarm, or blows cool air for a few minutes during defrost, is usually working normally. Air that stays cold after you’ve checked the thermostat, fan setting, filter and breakers means something needs repair. Call for service, and use emergency heat to stay warm until it’s fixed.
Related guides: Can a Heat Pump Keep Up With a Texas Freeze?, Heat Pumps vs. Electric Resistance Heat for Central Texas Homes, What’s Included in an HVAC Tune-Up? and Repair or Replace? Deciding What’s Best for Your HVAC System.
About Gold Eagle Services: This guide comes from the team at Gold Eagle Services, a family-run Austin HVAC, indoor air quality and mold remediation company founded in 2017. We’re licensed (TACLA119235 and RCO1783), insured and bonded, and we serve homes across the greater Austin area.
Need help with this in your home? Learn about our heat pump repair and service, or call 512-489-4653 to schedule a visit.
