The short answer
A heat pump blowing cool air in winter is often working: its air runs 85–100°F versus 120–140°F from a furnace, per Carrier. It also cools during defrost. Air that stays cold points to a thermostat setting, reversing valve, low refrigerant or backup heat; HomeGuide puts leak repair at $200–$1,500.
Key points
- Heat pump supply air runs cooler than a gas furnace's, so lukewarm air at the register can be normal.
- A few minutes of cool air while the outdoor unit steams is a defrost cycle, not a failure.
- Check the thermostat mode, fan setting, breakers, filter and outdoor unit before you call.
- Air that stays cold for more than a defrost cycle usually means a reversing valve, refrigerant or backup heat problem.
- If the house is losing heat, switch to emergency heat and call; don't keep resetting the system.
Cool air for a few minutes and then warm again is normal on a heat pump. When it stays cool, start with the thermostat and fan setting, because the fan on On pushes room-temperature air between heating cycles.
Why does heat pump air feel cooler than furnace air?
A gas furnace heats air with a flame. A heat pump moves heat out of the outdoor air with refrigerant, and the air it delivers is noticeably cooler. Carrier's heat pump troubleshooting page puts heat pump supply air at around 85–100°F during heating, compared with roughly 120–140°F from a gas furnace. Your skin is close to 90°F, so the low end of that range can feel like a draft even when the system is heating.
That's the biggest surprise for people who move from a furnace to a heat pump, or who have a dual-fuel system and notice the difference when it switches over. The heat pump makes up for the cooler air by running longer at lower output, which is also how it saves energy. The better test is the thermostat: if the room holds its setpoint, the system is doing its job.
At 0°F with a cold-climate model. Heat pumps lose capacity as the outdoor temperature falls. A cold-climate model keeps producing heat well below zero: to earn ENERGY STAR's cold-climate label, a heat pump must keep at least 70% of its 47°F heating capacity at 5°F, per ENERGY STAR's key product criteria. On a zero-degree night, expect long run times, supply air on the cooler side and backup heat or the furnace helping out below your house's balance point. Our guide to cold-climate heat pumps in Minnesota covers what these systems can carry on their own.
Can the defrost cycle make a heat pump blow cool air?
In heating mode the outdoor coil runs below freezing and collects frost. Every so often the system reverses to melt it off. Carrier says a typical defrost cycle lasts about 5–10 minutes. You'll see the outdoor fan stop and steam rise, and indoors the air may run cool until the cycle ends, unless backup heat or the furnace fills in. Our defrost cycle guide walks through what that looks and sounds like.
Cool air for a few minutes, then warm air again: normal. Cool air that doesn't come back to warm: keep reading.
Check these first
Go in this order. Each step is safe for a homeowner, and the first three solve a lot of calls.
- Thermostat. The system should be set to Heat (or Auto), not Cool, and the setpoint should be a few degrees above room temperature. Set the fan to Auto. With the fan on On, the blower runs between heating cycles and pushes room-temperature air that feels cold. If the display is blank, replace the batteries.
- Breakers and the furnace or air handler switch. A heat pump usually has its own breaker for the outdoor unit, one for the indoor air handler or furnace, and often separate breakers for electric heat strips. Look for any that are tripped. The service switch near the indoor unit (it looks like a light switch) should be on. A breaker that trips a second time stays off until a technician has looked.
- Filter. A clogged filter chokes airflow, and a heat pump is more sensitive to low airflow than a furnace. Carrier recommends checking the filter every 60–90 days. Replace it if you can't see light through it.
- Outdoor unit clear. Brush snow off the top and pull drifts away from the sides by hand. Carrier says a light frost layer under 1/4 inch is normal and should clear in defrost; ice thicker than that, or ice that doesn't clear, is not. Don't chip at ice or pour hot water on the coil.
- Condensate. In winter the indoor coil doesn't make much water, but if the air handler or furnace sits over a drain pan with a float switch, a full pan can shut the system down. If the pan is full or the drain line is frozen or plugged, turn the system off and call. Our post on clogged condensate drains explains what the float switch does.
When the cold air is a fault
Stuck in cooling: thermostat setting or reversing valve
A heat pump switches between heating and cooling with a reversing valve, controlled by a wire usually labeled O or B at the thermostat. Some brands power that valve in cooling and others in heating, and the thermostat has an installer setting to match. If it's set backward, you get cooling when you call for heat and heat when you call for cooling. That's most common right after a new thermostat goes in, and the fix is the O/B setting in the thermostat's installer menu.
If the thermostat hasn't changed and the air is still cold, the valve itself may be sticking. Carrier lists a faulty reversing valve among the causes of a heat pump that won't heat. A technician checks whether the valve is getting its signal and whether it's shifting.
Low refrigerant from a leak
A heat pump that's low on refrigerant moves less heat, so the air comes out lukewarm, the outdoor coil can ice up faster and backup heat runs more than it should. Refrigerant doesn't get used up. If it's low, there's a leak, and adding refrigerant without finding the leak only buys time. National cost guides such as HomeGuide put a refrigerant leak search and repair at $200–$1,500.
Backup heat that isn't coming on
On an all-electric system, electric heat strips in the air handler cover defrost and the coldest hours. If a strip breaker has tripped or an element has failed, the house heats fine on a mild day and falls behind on a cold night, with cool air during every defrost. On a dual-fuel system, the backup is the furnace, and a furnace that won't light gives the same symptom. Our post on aux heat vs emergency heat explains how the thermostat brings backup heat on.
Outdoor unit not running
If the indoor blower runs but the outdoor fan and compressor are silent (and it's not in defrost), the indoor unit is just moving air. Causes range from a tripped outdoor breaker to a failed fan motor or capacitor. National cost guides such as HomeGuide put an outdoor fan motor at $200–$700.
What does a technician check when a heat pump blows cold air?
A technician reads the thermostat configuration, including the O/B setting, and checks that the reversing valve shifts. They measure the temperature of the air going into and coming out of the air handler, check the refrigerant charge and look for leaks, test the heat strips or the furnace, and check the defrost control and the outdoor fan. Airflow matters too, because a restricted filter or duct system makes every other problem worse.
When to stop and call
Stop checking and call if the air stays cold for longer than a defrost cycle, a breaker trips a second time, the outdoor coil stays encased in ice, the pan is full of water or you hear grinding from the outdoor unit. Don't open electrical panels on the outdoor unit, touch the capacitor or reset the system over and over. If the house is losing heat, switch the thermostat to emergency heat so the backup runs by itself, and call.
The $79 trip charge on a service call is waived once you approve the repair, and the price is written and flat-rate before any work starts. If the heat pump is old enough that replacement makes more sense, our installed range is $7,500–$14,500. See our heat pump service page, heat pump service in Minneapolis or in Saint Paul. We're open 7 days, 7am–9pm, with priority for homes that have lost heat. Call 612-429-3465.
Common questions about heat pumps
Can a thermostat setting make a heat pump blow cold air?
Yes. Cool mode or a fan set to On will both do it. So will a reversing-valve setting that's backward, usually labeled O/B in the installer menu, which gives you cooling when you call for heat. That mix-up tends to show up right after someone installs a new thermostat. Put the old setting back or call the installer.
Should I switch to emergency heat if my heat pump blows cold air?
Only if the heat pump has actually failed and the house is losing temperature: the outdoor unit won't run, the coil stays iced solid, or the air stays cold long after a defrost. Emergency heat runs only the backup, which costs more with electric strips. Switch it on to stay warm, then call for service and switch back after the repair.
How warm should heat pump air feel at the register?
A heat pump's supply air typically measures 85–100°F, per Carrier, which feels cool against your skin even though it is warmer than the room. A furnace delivers 120–140°F. If the air reads close to room temperature while the thermostat is calling for heat, something is wrong and a technician should measure it.
Is a heat pump blowing cold air an emergency in a Minnesota winter?
It turns urgent once the house starts losing temperature, since the heat pump may be your main heat. Switch to emergency heat to stay warm, or let the gas furnace run if you have a dual-fuel setup, and call for service. We are open 7 days, 7am–9pm, and no-heat calls get priority.
Sources
- Carrier's heat pump troubleshooting page carrier.com
- ENERGY STAR energystar.gov
- HomeGuide: AC refrigerant recharge costs homeguide.com