Short answer
Wait 10 to 15 minutes first. In cold, damp weather the heat pump stops to melt frost off the outdoor unit, and the air feels cool while it does. Steam from the unit is normal. Then make sure the thermostat is on "Heat", a few degrees above room temperature, replace a clogged filter and sweep snow away from the unit. If the air stays cold, call a technician.
Safety first
Never open the panels of the outdoor unit, and do not chip or scrape ice off it. Clear snow with a broom, not a shovel against the unit.
How to check a heat pump that blows cold air
1Cool air inside, steam outside
In cold, damp weather the outdoor unit frosts up. Every so often it stops heating to melt the frost: that is the defrost cycle.
Read all the steps
- Cool air inside, steam outside. In cold, damp weather the outdoor unit frosts up. Every so often it stops heating to melt the frost: that is the defrost cycle.
- Give the defrost cycle 15 minutes. The outdoor fan stops, you may see steam and hear a whoosh. It usually ends within 15 minutes, the fan starts again and the heat comes back.
- Thermostat on Heat, a few degrees higher. Set it to "Heat", a few degrees above room temperature, with the fan on "Auto". On "Cool" or with the fan on "On", the vents blow cool air.
- Replace a clogged filter. A dirty filter cuts the airflow and makes a heat pump struggle. If it looks gray, put in a new one of the same size.
- Sweep the snow away from the unit. Gently brush snow off the top and away from the sides, and keep about two feet clear all around. Warm air should follow.
- Still not fixed? Call an HVAC contractor Especially if: the vents blow cool air for more than 30 minutes at a time, or on every cycle.
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Why heat pump air feels cooler
A heat pump moves heat from the outside air into the house. The air at the vents is warm, but cooler than the hot blast of a gas furnace, so it can feel cool on your hand. It runs longer and steadier instead. In very cold weather, backup electric heat helps it keep up, and the thermostat may show "Aux".
What not to do
- Do not chip or scrape ice off the unit. The fins and coil bend and puncture easily.
- Do not switch to "Emergency heat" just because the air feels mild. It runs only the backup heat, which costs much more.
- Do not cover the unit with a tarp while it runs.
- Do not open the panels of the outdoor unit.
When to call an HVAC technician
- The vents blow cool air for more than 30 minutes at a time, or on every cycle.
- The outdoor unit is covered in thick ice that does not melt.
- The outdoor fan does not spin, or the unit hums, rattles or grinds.
- The heat pump breaker trips again after one reset.
- The thermostat shows "Aux" or "Emergency heat" all the time.
Frequently asked questions
Why is my heat pump blowing cold air in heat mode?
Most often it is in the defrost cycle, which lasts a few minutes. If it lasts longer, check that the thermostat is on "Heat" with the fan on "Auto", replace a dirty filter and clear snow from the unit. Low refrigerant or a stuck reversing valve need a technician.
How long does a heat pump defrost cycle last?
Usually less than 15 minutes, and it can repeat every 30 to 90 minutes in cold, damp weather. Steam and a whooshing sound during defrost are normal.
Is it normal for a heat pump to blow lukewarm air?
Yes. Heat pump air comes out warm but cooler than furnace air, so it can feel mild. If it feels cold after 15 minutes, check the thermostat and the filter.
Should I use emergency heat when it is very cold outside?
Not just because it is cold. The heat pump turns on its backup heat by itself when it needs to. Use emergency heat only if the outdoor unit is damaged or iced over, and call a technician.
Why is steam coming out of my heat pump?
It is frost melting during the defrost cycle, and that is normal. Smoke or a burning smell is not: set the thermostat to "Off" and call.