The first frosty mornings bring the same question every year: "My heat pump is blowing cold air. Is it broken?" Most of the time, it's doing exactly what it's built to do. Here's how to tell the difference.
Why heat pump air can feel cool
A heat pump doesn't burn anything. It pulls heat out of the outdoor air and moves it inside, so the air from your vents is warm, usually somewhere in the 90s, not hot like a gas furnace. Hold your hand to a register and it can feel cool against your skin, even while the house is warming up. If the room temperature is climbing, the system is working.
The defrost cycle is normal
When it's near freezing and damp, which describes a lot of Southern Maryland winter mornings, frost builds up on the outdoor coil. Every so often the heat pump runs a defrost cycle to melt it off. While it does:
- The outdoor fan stops and you may see steam rising from the unit. That's melting frost, not smoke.
- You may hear a whoosh when it switches in and out of defrost.
- The air inside can feel cooler for a few minutes.
A defrost usually lasts about 5 to 15 minutes. Then normal heat comes back.
Aux heat vs. emergency heat
Most heat pumps have a backup heat source, usually electric heat strips in the indoor unit (or a gas furnace on a dual-fuel system). Your thermostat may show it two ways:
- Aux heat comes on by itself. When it's very cold, during defrost, or when you bump the thermostat up several degrees at once, the backup helps the heat pump catch up. Seeing "AUX" now and then is normal.
- Emergency heat is a setting you choose. It shuts the heat pump off and runs only the backup heat. It's meant for when the outdoor unit isn't working, and it costs a lot more to run, so don't leave it on as a "boost."
If your thermostat shows aux heat running most of the day, even on milder days, something is keeping the heat pump from doing its share. That's worth a look.
Quick checks before you call
- Make sure the thermostat is set to Heat, not Cool, and the fan is on Auto. With the fan on On, it blows air between heating cycles, and that air feels cool.
- Change the filter. A clogged filter cuts airflow and makes everything work harder.
- Look at the outdoor unit. A light white frost is normal. A thick block of ice that doesn't clear after an hour or two is not.
- Keep leaves, snow and mulch at least 2 feet back from the unit.
- Skip the big nighttime setback. Turning a heat pump down many degrees overnight means the backup heat does the work in the morning. A degree or two works better.
Never chip or pry ice off the coil. It's easy to puncture a refrigerant line.
When to call us
- The outdoor unit stays iced over
- The air from the vents stays cool for more than 20 to 30 minutes and it's not in defrost
- Aux or emergency heat seems to run all the time, or your electric bill jumps
- You hear grinding, banging or loud buzzing from either unit
We repair heat pumps of most brands all over St. Mary's and Calvert. Book a heat pump repair online, or call (301) 880-3248, Monday through Friday, 8 AM to 5 PM. If your heat pump is getting older and struggling every winter, it may be worth a look at a new heat pump. Today's models heat far better on cold days than the ones from 15 years ago.