If your heat pump blows cool air for a few minutes while steam rises from the outdoor unit, it’s most likely in defrost mode, and that’s normal. It becomes a problem when the cold air runs well past 15 minutes, the outdoor unit is wrapped in thick ice, or the system never seems to warm the house. After a Front Range snowstorm, drifts and frost on the outdoor unit are the usual trigger.
Below is a table that separates normal from not normal, the checks you can do safely, and the signs that mean it’s time to call. If you’d rather skip ahead, book a repair online or call us at (303) 945-4319.
Call for help first if you notice any of these
- Smoke or a sharp burning plastic or electrical smell. Turn the thermostat off and leave the system alone. Call us.
- Ice on the refrigerant lines, an outdoor fan that won’t spin after the ice melts, or grinding and banging noises. Turn the thermostat off and call us.
- A gas smell, if you also have a gas furnace for backup. Leave the house on foot and call 911 or your gas utility from outside.
- No heat in freezing weather with young children or older adults at home. Call us now at (303) 945-4319.
Normal or not? Match what you notice
| What you notice | Normal? | What to do |
| Cool air for a few minutes, steam rising, outdoor fan stopped | Yes, defrost mode | Wait. Heat should return, typically within 3 to 15 minutes |
| Air feels warm but not hot like a furnace | Yes | Nothing. Heat pump air is gentler than furnace air |
| A thin layer of frost on the outdoor unit that clears | Yes | Nothing |
| Cold air that lasts well past 15 minutes, or defrost keeps repeating without the house warming | No | Check the thermostat, filter and outdoor unit, then call |
| A thick shell of ice over the coil or fan | No | Turn the system off, clear snow safely, and call |
| Thermostat in Cool mode, or fan set to On | No, a setting | Change it yourself |
| Cold air with no steam, no ice and long run times | No | Call. This points to refrigerant, the reversing valve or controls |
What defrost mode looks like
In cold, damp weather the outdoor coil frosts over, and the heat pump briefly runs in reverse to melt the ice. While it does, the air from your vents turns cool, the outdoor fan stops, and white steam rises from the unit. Trane describes defrost as a normal part of cold-weather operation, and the steam is melting ice turning to vapor.
A cycle typically runs 3 to 15 minutes, then the system goes back to heating. Some noise changes, a whoosh from the refrigerant switching direction, and water dripping under the unit are normal too.
Heat pump air feels cooler than furnace air
Heat pump air is warm, but it usually doesn’t feel as hot as the air from a gas furnace. If you switched from a furnace, the difference can feel like cold air when nothing is wrong. Judge it by whether the house reaches the temperature you set, not by how the air feels on your hand.
Check the thermostat and filter first
These checks cause more “cold air” complaints than any failed part, and you can do all of them safely.
- Set the mode to Heat, not Cool.
- Set the fan to Auto. On makes the blower run between heating cycles and push out unconditioned air.
- If you have a smart thermostat, confirm it’s set up for a heat pump rather than conventional heat.
- Replace a dirty filter. Our online shop carries filters.
- Make sure the breakers for both the indoor unit and the outdoor unit are on. If one trips again after a reset, stop and call us.
Clear snow and ice around the outdoor unit, the safe way
Blocked airflow makes the coil frost faster than the defrost cycle can clear it. After a snowstorm, check that drifts haven’t piled against the unit.
- Turn the thermostat to Off.
- Clear snow with a gloved hand or a soft broom. Don’t use a shovel, and never chip at ice or use sharp tools on the coil.
- Don’t pour hot water on the unit or use a heat source on it. Improper thawing can damage it.
- Keep about two feet clear on all sides.
- Turn the thermostat back to Heat and watch for the unit to run a full defrost and return to heating.
If ice comes back quickly or the unit stays encased, the defrost system may need service. If the house is getting cold while you wait, many thermostats have an Emergency Heat setting that runs backup heat. It costs more to run, so use it only until a technician arrives.
Backup heat isn’t kicking in
On very cold days a heat pump needs help from backup heat to keep up. If the backup never comes on, the air from the vents can feel cold even though the system is running. The reverse is also a warning sign: if your thermostat shows Aux or Emergency Heat all the time, the heat pump itself may not be doing its job, and your electric bill will show it.
This one is for a technician. The backup heat and its controls involve high-voltage wiring that isn’t safe to test yourself.
Refrigerant, the reversing valve or the defrost controls
If there’s no ice, no steam, no wrong setting and the air is still cold, the cause is usually inside the system. A reversing valve stuck in cooling mode sends cool air no matter what the thermostat says. A refrigerant leak lowers the system’s heating output, and a failed defrost control or sensor lets ice build up that never clears.
None of these are homeowner repairs, and refrigerant can only be handled by a licensed technician.
When to call Comfort Pros
Call if the air is still cold after the checks above, if ice keeps coming back, if backup heat runs constantly, or if any row in the table says call. We find out where the system is failing, whether that’s the thermostat setup, defrost controls, reversing valve, outdoor fan or refrigerant circuit.
We’re family owned, with 15 years in business and more than 40 years of combined team experience, and we service and install heat pumps across the north Denver metro. Book a repair online or call (303) 945-4319. 5.0 from 678 Google reviews.
What Front Range winters do to outdoor units
A heat pump can work well in Colorado when it’s sized and installed correctly, but our winters are hard on outdoor units in a specific way. A snowstorm pushes drifts against the cabinet in Westminster, Arvada, Broomfield and Thornton, and cold, damp mornings frost the coil, so the unit needs clear airflow to defrost. Walking out after each storm and checking the unit does more than any other habit.
For how heat pumps perform in our climate, read our guide to cold-climate heat pumps in Denver. If your system is old and the problems keep coming back, our rebates page lists current options for replacing it.
Frequently asked questions
How long should a heat pump blow cold air in defrost mode?
Typically 3 to 15 minutes. If cold air continues well past that, or the cycle repeats and the house doesn’t warm up, call for service.
Why is steam coming off my heat pump?
It’s usually melting frost turning to vapor during a defrost cycle. Steam that fades within a few minutes is normal. Thick smoke with a burning smell is not, so turn the system off and call.
Should I turn my heat pump off when it blows cold air?
Not during a normal defrost, because it needs to finish. Turn it off if you see smoke or a burning smell, a solid block of ice, or hear grinding noises.
Should I cover my heat pump for the winter?
No. Heat pumps are built for outdoor use, and a tight cover can keep the defrost cycle from working. Keep snow and debris clear instead.
Is it normal for heat pump air to feel lukewarm?
Yes. Heat pump air is warm but usually feels cooler than furnace air. If the house reaches the temperature you set, it’s working.
Heat pump still blowing cold?
Book a repair online or call us at (303) 945-4319. We’re Comfort Pros Heating and Air Conditioning, family owned, with 5.0 from 678 Google reviews.
