It is the first really cold morning of the year in Gilbert. You glance out the window and the outdoor unit is puffing steam like a kettle. The thermostat says “aux heat,” and the air coming out of the vents feels warm but not exactly toasty. So is something wrong with your heat pump?
Most of the time, no. Heat pumps behave differently in winter than they do in summer, and a few of the things that worry people most are actually signs the system is doing its job. Some winter behavior does mean it is time for a technician, though, and it helps to know which is which before a cold snap. We are Preferred Comfort Heating & Cooling, a local HVAC company serving Gilbert, Batesburg-Leesville and the communities around Lake Murray, and this is the same walk-through we give our neighbors on the phone.
Normal or worth a call? A quick guide
Here is the short version. If what you are seeing is in the left column, your heat pump is most likely fine. If it is in the right column, give us a call.
| NORMAL IN WINTER | WORTH A CALL |
|---|---|
| Steam rising from the outdoor unit for a few minutes, then stopping | Thick ice covering the outdoor coil that does not clear |
| Aux heat on a very cold morning | Aux heat running all day in mild weather |
| Air that feels warm, but not as hot as a furnace | Cool air for long stretches, or a house that will not reach the set temperature |
| A whoosh or click when the unit switches modes | New grinding, squealing or banging noises |
| Longer, steady run times on cold days | Running nonstop without keeping up, or tripping a breaker |
Why is steam coming off my outdoor unit?
On cold, damp mornings, moisture in the air freezes onto the outdoor coil. A light coat of frost is expected, and your heat pump has a built-in way to deal with it called a defrost cycle. For a few minutes, the system reverses itself to warm the outdoor coil and melt the frost. While that happens, the outdoor fan may stop, you may hear a whoosh or a click as it switches over, and the melting frost rises off the unit as steam. Then it switches back and goes on heating your house.
That steam is the part that sends people to the phone, and it is completely normal. What is not normal is a unit that stays encased in thick ice, or ice that keeps building on the coil and never clears. If you see that, do not chip at it with a screwdriver or pour hot water on it, since the coil fins are thin and easy to damage. Turn the system off at the thermostat and call us.
What does “aux heat” mean on my thermostat?
Most heat pump systems have a backup heat source, often electric heat strips in the indoor unit. When it is very cold outside, during a defrost cycle, or when you bump the thermostat up several degrees at once, the system brings that backup heat on to help. Your thermostat shows it as “aux heat” or “auxiliary heat.” Seeing it on a frosty morning is normal.
Seeing it all day on a mild afternoon is not. If aux heat runs constantly when it is not that cold out, the heat pump may not be carrying its share of the load, and backup electric heat costs more to run. That is worth a service call.
You may also have an “emergency heat” setting. That is a manual switch meant for when the heat pump itself is not working, not something to use every day. If you have had to flip it on to stay warm, that is your sign to call us.
Why does the air from my vents feel lukewarm?
A heat pump does not make heat the way a gas furnace does. It moves heat from the outside air into your house, so the air at the vents comes out warmer than the room but not as hot as furnace air. Heat pumps also tend to run longer, steadier cycles in cold weather instead of short blasts.
The real test is simple: is the house holding the temperature you set? If it is, the system is working, even if the air feels mild on your hand. If the house keeps falling behind, or the air feels cool for long stretches, something needs a look.
What can I check myself before I call?
A few quick checks solve a surprising number of winter heating complaints:
- Filter. Pull it and look. During heavy heating months, check it monthly and replace it when it is dirty. A clogged filter makes the whole system work harder.
- Thermostat. Make sure it is set to heat, replace the batteries if it uses them, and raise the temperature a couple of degrees at a time instead of all at once.
- Outdoor unit. Keep leaves, pine straw and shrubs clear so air can move around it. Do not cover a heat pump in winter, because it needs that airflow to heat your home.
- Vents and returns. Make sure furniture, rugs or holiday decorations are not blocking them.
- Breaker. If the system is completely off, check the breaker once. If it trips again, leave it off and call us.
When should I call Preferred Comfort?
Call us if your heat pump runs nonstop without keeping up, blows cool air for long stretches, stays iced over, makes new grinding or squealing noises, trips a breaker, or shows aux heat in mild weather. Any of those is worth a technician’s time.
If you have not had a heating check this fall, our post on fall heating tune-ups explains what a visit covers and how to decide whether it is worth it. A lot of winter surprises show up first as small things a tune-up can catch.
We work Monday through Friday, 8am to 5pm, and we strive to get to service calls within 24 to 48 hours, so you are not left waiting weeks for help when the house is cold.
Planning ahead? Preferred Comfort Care Plan members get regular maintenance visits, discounts on parts and replacement, and one free service call during normal business hours. If your system is near the end of its life, we partner with Wells Fargo on promotional financing rates throughout the year, so ask what is available. And with any approved replacement estimate, we can loan you a space heater at no charge until your new equipment arrives.
Local help from people who live here
Preferred Comfort was founded in 2023 with a simple goal: give people a more trustworthy HVAC experience. Our team brings 80 years of combined experience, we were Voted Among the Best in 2024 and 2025, and we are licensed, insured and BBB accredited. We serve Gilbert, Batesburg-Leesville, Lexington, Chapin, Irmo and the communities all around Lake Murray. You can see more about our work in the area on our Lexington HVAC services page.
Is your heat pump doing something that is not on the normal list? Call Preferred Comfort at (803) 580-9553, Monday through Friday, 8am to 5pm, or visit our HVAC repair page to see how service works. Tell us what you are seeing, whether it is ice, aux heat or cool air, and we will get a technician out to take a look. Facing a big repair quote from someone else? We offer a free second opinion on repairs over $1,500.