Why does outside fan run when heat is on?

Author: Lucie Russel  |  Last update: Monday, November 24, 2025

To put it simply: Yes, the outside fan should run when your heat pump is in heating mode. Here's why. The outside fan is responsible for the transfer of heat from the outdoor air to the refrigerant coils inside the outdoor unit. Even in cold weather there is some heat present in the outdoor air.

Should an outside unit fan run when heat is on?

The outdoor span should be continually spinning whenever the system is working to reach the temperature that's set at your thermostat. It should only stop once this temperature has been achieved. If the fan won't budge, your living space won't get any conditioned air.

Is the outside unit supposed to spin when heat is on?

The fan in the outside unit should be spinning while the heat pump is trying to reach the temperature you set on the thermostat. Also, it should stop spinning once it reaches that temperature. If the fan doesn't move, your home won't get the cool or warm air it needs.

Why does my fan run continuously in heat mode?

Faulty Thermostat: If both the fan and either the cooling or heating system are running unexpectedly, you may have a faulty thermostat (2). A malfunctioning thermostat may not properly send the on/off commands to the fan, causing it to run continuously. In this case, it may be necessary to replace the thermostat.

Why is my fan blowing cold air when heat is on?

This is a common and normal condition of a working system if the fan switch is ON. With the fan running constantly, cool air will come out whenever the set temperature is reached, and will continue to come out until the heat turns on. When the system is heating again, the air will become warm.

What if the Outdoor (Condenser) Fan Runs During Heat Pump Defrost?

Why is my heat on but blowing cold air?

Common signs of dirty air filters include long heating cycles and overheating issues. The average overheating issue will cause your heater to blow cold air throughout your home. To restore the flow of warm air in your house, we recommend replacing the contaminated air filter with a new one.

Why is fan running when heat is off?

When the thermostat indicates no heat is needed, the fan limit switch turns off as the burners cool. If your HVAC fan keeps running but there's no heat, your fan limit switch may be set to manual override.

Why is the fan constantly running on my furnace?

If your furnace fan won't turn off, you most likely have one of these 3 problems: Your furnace fan limit switch is set to “manual override” The fan limit switch is faulty and needs to be replaced. There's a problem in your thermostat wiring.

Should the fan be on auto when the heat is on?

While the answer is that there are pros and cons to both, I personally recommend using the “auto” function over the “on” function for your furnace fan. The amount of money you save and the boost in energy efficiency is the reason why. I also suggest having a smart thermostat installed in your home.

Should a heat pump fan run all the time in winter?

The heat pump fan typically runs continuously during the winter, even when the system is in heating mode. Its primary function is to pull in the outdoor air and circulate it over the outdoor coil, where heat exchange takes place.

Why is my outside unit running when the heat is on?

There are a few reasons why this might happen: it may be an easily-fixed mix-up in your thermostat's HVAC settings, the need for some basic maintenance, or a potentially-serious electrical problem.

Why is my outside AC unit running during the winter?

So why is this happening? During cold weather, your air conditioner is running because it's a heat pump. A heat pump does double duty for heating and cooling. It moves heat instead of generating it.

Should the AC be on when the heat is on?

Simply put, running the A/C and heater will dehumidify and remove moisture from the air. To explain further, the relative humidity is the percentage to the dew point for droplets to form. This point increases as temperatures rise.

Should fans be on during heat?

Keeping the fan on creates a more even distribution of heating and cooling, circulating the air if you have cold or hot spots in your house, like a bedroom above a garage. Less frequent starts and stops of the fan can reduce the stress from startup, and potentially help extend it's lifespan.

What is the purpose of the fan on the outside AC unit?

The outdoor unit also has a fan that pulls air through the outdoor coil. This process allows the system to release heat that has been absorbed from inside the home. Central, split-system, ductless, and packaged air conditioners all use fans.

Does the AC compressor run when the heat is on?

That depends on your system. If your “heater” is a heat pump, then the compressor is used for both heating and cooling. If you have a traditional furnace and air conditioner, then the compressor should not be on when heating.

Is the outside fan supposed to run when the heater is on?

To put it simply: Yes, the outside fan should run when your heat pump is in heating mode. Here's why. The outside fan is responsible for the transfer of heat from the outdoor air to the refrigerant coils inside the outdoor unit. Even in cold weather there is some heat present in the outdoor air.

Should the thermostat be on auto or on for heat in winter?

The Advantages of “Auto”

Higher Energy Efficiency — Using the “AUTO” setting helps increase energy efficiency by reducing the amount of energy used to keep your home comfortable. This means you're wasting less electricity and exposing your furnace system to less constant heating.

Why is my heater blowing cold air?

With a furnace blowing cold air, the first question you should ask is if the furnace has been turned ON. Two thermostat issues that could cause your furnace to blow cold air include (1) your thermostat is still set to COOL, not HEAT and (2) your thermostat fan is set to ON, not AUTO.

Is it OK to run furnace fan constantly in summer?

Although it is perfectly safe to run HVAC continuously, there are a few times you should shut it down. First, if your home is experiencing high summer temperatures and you have ductwork in the attic. It is difficult for even the best-insulated systems to fight off extreme temperatures.

Is it expensive to run furnace fan all the time?

If we assume an average of 10 hours on and 14 hours off per day, energy costs are reduced by 60% to about $18 per month or $215 per year. Bottom line – If you run the fan in AUTO mode, you'll save about $300 per year.

How do I stop my HVAC fan from running?

The Fan Limit Switch is in Manual Override Mode

This will ensure that your furnace fan runs only when necessary and not continuously. The fan limit switch is typically located near the blower motor or in the control box. It just requires a press from your finger to behave accordingly.

Why is the fan always running on my furnace?

Yes, if the fan continues to run after setting the thermostat to "AUTO," it could indicate a malfunction. Common culprits include a faulty fan limit switch, a stuck relay, or issues with the furnace's control board. These components regulate when the fan turns on and off, and if they fail, the fan may run indefinitely.

Why does my heat keep running after it has reached the set temperature?

A dirty air filter can get clogged and reduce air flow through your home's heating system. This means the air your furnace is heating isn't reaching your living spaces and causing your furnace to cycle on more often and work longer while it's on.

Why won't the furnace fan shut off?

Problem 1: Incorrect thermostat settings The most common reason for a furnace fan that won't shut off or a furnace blowing cold air and won't shut off is the wrong thermostat settings. The solution: Check the thermostat settings. The fan setting should be on AUTO. If it's set to ON, the furnace fan won't shut off.

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