Start with the thermostat, not the unit itself
A heat pump works through your thermostat, not by adjusting anything on the outdoor unit. You control temperature, mode (heating or cooling), and fan speed entirely from the wall panel inside your home. Most heat pumps use a standard programmable or smart thermostat that looks similar to what you'd find on a furnace or air conditioner system.
The outdoor unit runs automatically once you set your thermostat. You should never need to touch the compressor, refrigerant lines, or any part of the exterior equipment during normal operation. If the outdoor unit is making noise, leaking, or not running at all, that signals a problem that needs a technician—not something you adjust yourself.
Key Takeaways
- Set your thermostat to heating mode in winter and cooling mode in summer; the heat pump switches between them automatically based on your setting.
- Keep your thermostat set to a steady temperature rather than swinging it up and down, because heat pumps work most efficiently when they run continuously at a lower output.
- The outdoor unit will cycle on and off throughout the day—this is normal operation, not a malfunction.
- In very cold weather, your system may set up electric resistance heating (backup heat) automatically; this is normal but uses more energy than the heat pump alone.
- Clean or replace your indoor air filter every one to three months, because a clogged filter reduces efficiency and can trigger the system to switch to backup heat.
Setting heating and cooling modes on your thermostat
Most heat pump thermostats have a mode selector with at least three positions: Heat, Cool, and Off. In winter, turn the dial or press the button to Heat. In summer, switch it to Cool. Some thermostats also have an Auto mode, which lets the system switch between heating and cooling on its own—useful in spring and fall when you might need both in a single day.
Once you've chosen your mode, set your desired temperature using the up and down arrows. The system will run until the indoor temperature matches what you've set. Unlike a furnace that heats in bursts, a heat pump runs continuously at a lower intensity, so you may notice the air coming from your vents feels less hot than a traditional heating system. This is normal and actually more efficient.
If your thermostat has a fan setting, leave it on Auto unless you want the fan running constantly. Auto means the fan only runs when the heat pump is actively heating or cooling. Continuous fan mode uses extra energy and doesn't improve comfort.
Understanding when your system cycles on and off
A heat pump that's working correctly will turn on and off throughout the day. It doesn't run nonstop—it cycles. When your home reaches the temperature you set, the compressor shuts down and the fan may continue for a few seconds to push out remaining warm or cool air. When the temperature drifts a degree or two away from your setting, the system starts again.
This cycling is efficient operation. A heat pump that runs constantly without stopping is actually a sign something is wrong—either the thermostat is set too high or too low, or the system isn't powerful enough for your space. If you notice your heat pump running almost without pause, check that your thermostat setting makes sense for the season, and contact a technician if the problem continues.
In cold climates, you may hear the outdoor unit make a hissing or gurgling sound during heating. This is refrigerant flowing through the system and is completely normal. A loud grinding, squealing, or rattling noise is not normal and means you should turn the system off and call for service.
What to do when backup heat activates
Most heat pumps have electric resistance heating (sometimes called auxiliary heat or emergency heat) built in as a backup. When outdoor temperatures drop below a certain point—usually around 35°F to 40°F—your system automatically switches on this backup heating to help the heat pump keep up. You'll see a light labeled "Aux Heat" or "Emergency Heat" appear on your thermostat.
This automatic set up is normal and necessary in cold weather. The heat pump alone becomes less efficient in very cold conditions, so the system adds electric heating to maintain your comfort without making the heat pump work harder than it should. However, backup heat uses significantly more energy than the heat pump alone, so your utility bill will rise during extended cold spells.
You should only manually switch to Emergency Heat mode if your heat pump stops working entirely and you need when ready warmth. In that case, switch the mode to Emergency Heat and call a technician right away. Running on backup heat alone for extended periods is expensive and should only be temporary.
Maintaining your air filter for consistent performance
The most important maintenance task you can do is replacing your indoor air filter regularly. A clogged filter restricts airflow, which forces your heat pump to work harder and can trigger it to switch to backup heat unnecessarily. Check your filter every month during heating and cooling season by sliding it out of its slot (usually near the furnace or air handler inside your home).
If you can see dust buildup on the filter, it's time to replace it. Most standard filters need changing every one to three months, depending on whether you have pets, allergies, or a dusty environment. Write the replacement date on your new filter with a marker so you remember when you installed it. Filters are inexpensive (usually $10 to $25) and take less than a minute to swap out.
If your thermostat shows a filter change reminder or your system switches to backup heat unexpectedly, check the filter first before calling for service. A dirty filter is the most common reason a heat pump seems to stop working properly.
Adjusting your thermostat for comfort and efficiency
Heat pumps work most efficiently when you set your thermostat to one temperature and leave it there. Constantly adjusting the temperature up and down forces the system to cycle more frequently and can trigger backup heat to set up. If you're cold, raise the temperature by 2 to 3 degrees and wait 15 to 20 minutes for the system to catch up—don't jump it up 5 or 10 degrees at once.
In winter, most people find comfort between 68°F and 72°F. In summer, 76°F to 78°F is typical. Every degree you lower in winter or raise in summer saves energy and money. If you're away during the day, lowering your winter setting by 5 to 10 degrees while you're gone and raising it back when you return can reduce your heating costs noticeably.
If your home has a smart or programmable thermostat, you can set a schedule so the temperature adjusts automatically at certain times. This is more efficient than manually changing it each day. Many modern thermostats also learn your habits and adjust on their own, which can help balance comfort and energy use.
Troubleshooting common operating issues
If your heat pump isn't producing heat or cool air, start with the thermostat. Confirm the mode is set correctly (Heat for winter, Cool for summer), the temperature setting is higher than the current room temperature (for heating) or lower (for cooling), and the system isn't set to Off. Check that your air filter isn't clogged. If all of these are fine and the system still isn't running, turn it off for 30 seconds and turn it back on—sometimes this resets a minor sensor issue.
If the outdoor unit isn't running at all, check that nothing is blocking it (snow, leaves, or debris) and that ice hasn't built up on the coils. A thin layer of frost on the outdoor unit during heating is normal, but thick ice means the system needs service. If the unit is clear and still not running, the problem is electrical or mechanical and requires a technician.
If your system is running but your home isn't reaching the temperature you set, the backup heat light should be on (which is normal in very cold weather). If backup heat isn't on and the system is running but not keeping up, your heat pump may be undersized for your space, or there may be a refrigerant leak. Both of these require professional service.
Frequently Asked Questions
Why does my heat pump run so much in winter?
Heat pumps run continuously at lower output rather than in short bursts like a furnace. This is normal and efficient. However, if it's running almost constantly without stopping, the outdoor temperature may be below the point where your system works well alone, triggering backup heat to run alongside it. This is expected in very cold climates and will increase your energy use during cold snaps.
Is it normal for the outdoor unit to be frosted over?
A thin layer of frost on the outdoor coils during heating mode is normal—the system is pulling heat from cold air. However, thick ice buildup that doesn't melt off is a problem. If you see heavy ice, turn the system off and call a technician. The system has a defrost cycle that should prevent excessive ice, and if it's not working, the heat pump won't operate efficiently.
Should I turn off my heat pump when I leave home?
No. Instead, lower the temperature setting by 5 to 10 degrees while you're away and raise it back when you return. Turning the system completely off and restarting it later makes it work harder to reheat your home, which uses more energy than straightforward running at a lower setting. A programmable thermostat can do this automatically for you.
What's the difference between the fan setting and the system running?
The fan setting controls whether the indoor fan runs only when the heat pump is actively heating or cooling (Auto mode) or continuously (On mode). Leaving it on Auto is more efficient because the fan doesn't run when the system isn't heating or cooling. Continuous fan mode circulates air but doesn't change the temperature and wastes energy.
Can I use my heat pump in spring and fall?
Yes. If your thermostat has an Auto mode, you can set it and let the system switch between heating and cooling as needed. This is useful during shoulder seasons when you might need heat in the morning and cooling in the afternoon. If your thermostat doesn't have Auto mode, you'll need to switch between Heat and Cool manually as the weather changes.