Heat Pump Blowing Cold Air? Aux Heat vs. Emergency Heat in Chesapeake, VA

A heat pump that blows cool air for a few minutes on a cold, damp morning is usually defrosting, and that’s normal. A heat pump that blows cold air steadily while the thermostat is set to heat has a problem. Here’s how to tell the two apart and what the AUX and EM HEAT lights on your thermostat mean.

Why Is My Heat Pump Blowing Cold Air?

Most of the time a heat pump blowing cold air in heat mode is doing one of three things: running a defrost cycle, sitting on the wrong thermostat setting, or blowing air that’s warm but cooler than you expect. A heat pump moves heat from outdoor air into the house, and the air at the vents usually runs about 90 to 110 degrees. That’s warm, but it’s below body temperature, so it can feel cool on your hand, especially if you’re used to a gas furnace. If the air feels lukewarm and the house is holding temperature, the system is working.

When the air is truly cold, the house keeps losing ground, or the cold air lasts longer than about 15 minutes, the usual causes are:

• The thermostat is set to COOL, or the fan is set to ON
• The outdoor unit is iced over and not clearing
• The outdoor unit isn’t running at all
• Low refrigerant from a leak
• A failed defrost control, sensor or reversing valve

Is It Normal for a Heat Pump to Blow Cool Air During Defrost?

Yes. On cold, wet mornings the outdoor coil collects frost, and the heat pump clears it by briefly reversing into cooling mode. During defrost the outdoor fan stops, you may see steam rising off the unit, and the air indoors can feel cool for a few minutes. Most systems turn on auxiliary heat during defrost to take the edge off, so the air should feel lukewarm rather than cold. Once the coil is clear, warm air returns.

Defrost is common here. Chesapeake, Norfolk and Virginia Beach average about 40 nights a year below freezing, and many more winter mornings sit just above 32 degrees with high humidity. Those damp, near-freezing mornings are when outdoor coils frost fastest, so the system may defrost several times in one morning. A light coat of frost that melts off every so often is normal. A solid block of ice that stays on the coil isn’t.

What Is the Difference Between Aux Heat and Emergency Heat?

Aux heat is automatic backup heat that helps the heat pump; emergency heat is a setting you turn on yourself that shuts the heat pump off. Both use the same backup source, which in most homes is a set of electric heat strips inside the indoor air handler. In a dual-fuel system the backup is a gas furnace instead. The difference is who’s in control and whether the outdoor unit is still running.

The thermostat usually calls for aux heat when it’s below about 40 degrees outside, when the heat pump is defrosting, or when you raise the setting more than 3 or 4 degrees at once. AUX on a frosty morning is expected. AUX for hours on a mild 50-degree afternoon means the heat pump isn’t keeping up and should be checked.

When Should You Use Emergency Heat on a Heat Pump?

Use emergency heat only when the outdoor unit has stopped working: it won’t run, it’s encased in ice that isn’t clearing, or it’s making grinding or banging noises. Switching to EM HEAT shuts the heat pump off and lets the backup heat the house by itself, which keeps you warm and keeps a damaged unit from running. Then call for repair.

Don’t use emergency heat just because it’s cold outside. Even on our coldest nights, which drop below 20 degrees only a handful of times a year, the heat pump and aux heat together will heat the house for less money. Electric heat strips turn each unit of electricity into one unit of heat. A heat pump moves existing heat in from outdoors, so it delivers more heat than the electricity it uses. Leaving emergency heat on for days, especially by accident, is one of the fastest ways to raise a winter power bill.

What Can You Check Before Calling for Repair?

Five quick checks solve a fair share of cold-air calls:

1. Thermostat mode. Set it to HEAT, not COOL or AUTO, with the setting above room temperature.
2. Fan setting. Set the fan to AUTO. On ON, the blower keeps moving air between cycles, and that air feels cool.
3. Emergency heat. If EM HEAT was switched on by mistake, switch it back to normal heat.
4. Breakers. A heat pump usually has two breakers, one for the outdoor unit and one for the indoor air handler. Check both, plus the disconnect switch next to the outdoor unit.
5. Outdoor unit and filter. Clear leaves, mulch or anything stacked against the unit, and make sure no gutter is dripping onto it. Replace a dirty air filter.

Don’t chip ice off the coil or pour hot water on it. The fins bend easily, and a damaged coil costs far more to fix than the ice.

When Does Cold Air Mean You Need Heat Pump Repair?

Call for repair when the outdoor unit stays iced for more than an hour, doesn’t run at all, or the house won’t reach temperature with the thermostat set correctly. Those signs point to a failed part, not a setting. The usual causes are a bad defrost sensor or control board, a refrigerant leak, a stuck reversing valve, or a failed outdoor fan motor or capacitor.

Some of these show up before the cold does. One Weather Makers customer wrote in a December review that during annual maintenance our technician “found faulty defrost sensors,” then got the part and came back the same day to make the repair.

Weather Makers repairs heat pumps of every major brand in Chesapeake, Virginia Beach, Norfolk, Suffolk, Portsmouth and northeastern North Carolina. Our NATE-certified technicians find the cause and give you a flat-rate price before any work starts. See our heat pump repair service for details.

Frequently Asked Questions

How cold is too cold for a heat pump in Chesapeake?

A standard heat pump keeps working through our winters, but it loses capacity as the temperature drops, which is why aux heat helps out on cold nights. A properly sized heat pump with working backup heat handles a Chesapeake winter. If the house can’t stay warm when it’s in the 30s outside, have the system checked.

Do ductless mini-splits blow cold air during defrost too?

Yes. A ductless mini-split is a heat pump, so it runs defrost cycles the same way. The indoor unit usually stops blowing for a few minutes, then resumes heating.

Get Your Heat Pump Checked by Weather Makers

If your heat pump is still blowing cold air after those checks, call Weather Makers at (757) 421-2665. We answer 24/7, so call rather than filling out a form when the heat is out. Comfort PLUS Club members get priority scheduling, no after-hours rates and 15% off repairs; see our maintenance plans.