How Cold Should You Expect Air Blowing Out From AC Be?

Josh Mitchell

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Josh Mitchell

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Key Takeaways

  • The air coming out of the AC should be blowing typically at 15-20°F lower than the desired temperature value or the value at which the thermostat is set at. 
  • You can accurately check the air blowing out of AC using a good quality infrared thermometer.
  • Both too high and too low a temperature differential is bad for your AC.

Worried about your AC performance? Check the blowing temperature!

It's a simple way to check your air conditioner's efficiency and performance at home without professional help.

However, to do this properly, you must know the temperature at which it should be blowing and how to measure it accurately.

In this guide, I'll answer the question 'What temperature should air from AC be blowing?" and show you how to measure the temperature like an HVAC professional so you can see just how your air conditioner is performing.

Air conditioners should typically blow out air 15-20 degrees Fahrenheit colder than the desired room temperature.

This 15-20 degree difference between the thermostat setting and the air temperature is called the 'temperature differential' or ‘evaporator Delta T.’

The exact temperature of the air coming from the supply vents will vary depending on the temperature you want the room to be.

I recommend keeping the temperature in your living space at 70-75 degrees Fahrenheit for maximum comfort.[1]

Therefore, the air coming from the AC should be 50-60 degrees.

TL;DR: Temperature blowing from the AC is cooler than the temperature you have set the AC at.

Why Air Coming From Supply Vents Should Be 15-20 Degrees Lower

  • Indoor air heat gain - as soon as the air leaves the return vents, it will immediately start to regain heat. The return air temperature must start colder to allow for this.
  • Humidity control - the cool air helps to dehumidify the indoor air.[2]
  • Comfort - the colder air from the AC helps provide instant relief from hot conditions even before the room cools down.
comfortable family in an air conditioned room

Do All ACs Have the Same Temperature Differential?

No, the temperature differential for air conditioners can vary depending on the size, system type, and specifications.

  • Standard, central air conditioning, and window AC units typically have a 15-20°F differential.
  • Portable, ductless, and mini-split ACs typically have a 10-15°F differential because they are usually smaller and offer more precise temperature control and airflow.
  • Powerful commercial HVAC units may have a 20-30°F differential because they can remove more heat in each cycle.
It can also vary slightly depending on your exact environment, humidity, and airflow, but the air coming out of vents should always be between 10-30°F lower than the set thermostat temperature.

TL;DR: The more powerful an AC the larger is the temperature differential. You know that an AC is working well, if the temperature differential between released air and desired value is 10-30°F lower.

What Is Supply and Return Air?

Supply air is the cold air that has been through your air conditioning system and blown back into your home.

Return air is the air that gets sucked from your house and into your air conditioning system. It’s the warm air that needs to be cooled.

Understanding the basic airflow of your air conditioner can help to explain the difference between the two:

  1. Warm return air is pulled into the air conditioner through return air vents.
  2. The return air passes over the evaporator coil in the AC system.
  3. The warm return air becomes cold supply air and is pushed back into your home through supply vents.
  4. Warm return air is pulled into the air conditioner again, and the cycle repeats until room temperature reaches the thermostat setting.

The difference between your return air temperature and supply air temperature is the 'temperature differential' or 'evaporator Delta T' - this represents how much heat the AC removes from the air as it passes through.

Important Note:

Supply and return air temperatures will drop as the cooled air lowers the temperature in your home.

How To Accurately Measure the Air Temperature Differential in Your AC System

I recommend using an infrared thermometer for easy measuring and exact temperature readings.

You can pick them up on Amazon for $30-$100, and I recommend a model like the ennoLogic Temperature Gun.

Here are the steps to follow:

  1. 1
    Find The Return and Supply Vents:
    Look for the vents that air flows in and out (or check the user manual). These are easy to find on most units.

    A central AC may have multiple return and supply ducts, so I recommend finding a supply and return vent near the air conditioning unit to get the most accurate readings.
  2. 2
    Let The AC Run:
    Set the thermostat to the desired room temperature and let it run for 15-30 minutes. This allows the unit to stabilize to give the most accurate readings.
  3. 3
    Measure the Supply Vent Temperature:
    Point the infrared thermometer at the supply vent with nothing blocking the direct line of sight. Press the measurement button for a few seconds until you get a reading.

    This is the temperature of the cooled air that’s passed through the AC evaporator coil.
  4. 4
    Measure the Return Air Temperature:
    Next, use the infrared thermometer on a return vent going into the air conditioner. This is the temperature of hot air entering your AC vent.
  5. 5
    Calculate the Temperature Differential:
    To calculate the Delta T (temperature differential), subtract the return air temperature from the supply air temperature. This is the heat energy removal as air passes over the AC evaporator coil.

Here’s a worked example for my home where the return air was 70°F, and the supply AC blow air was 53°F:

Return air temperature - supply air temperature = Delta T (ΔT)

70 - 53 = 17

The Delta T (ΔT) is 17°F, comfortably within the 15-20°F ideal temperature range.

Air Conditioner Output Temperature Chart

Below is a quick summary to help you determine the right temperature for each thermostat setting:

Thermostat Temperature (degrees Fahrenheit)

Ideal AC Output Temperature (degrees Fahrenheit)













What Happens If the Temperature Differential Isn't Within The Ideal Range?

An incorrect temperature differential can lead to:

  • Uneven cooling or blowing warm air
  • Higher energy bills
  • Shortened equipment lifespan
  • Frozen evaporator coils and other internal damage

There are two different issues:

Low Differential: If the differential (Delta T) is under 15°F, the AC isn’t blowing cold enough air to cool the room properly.

This makes it challenging to maintain set temperatures in your home.

High Differential: A high differential (Delta T) of more than 20°F means the air is blowing too cold.

This decreases the efficiency of the unit and can lead to humidity issues.

Useful Note:

Have an HVAC professional inspect and perform AC repair on your system annually to keep it in working order.

An incorrect differential is usually caused by one of the following common AC issues[3]:

  • Low Refrigerant Levels:
    If your AC doesn’t have enough refrigerant, it can’t properly absorb the heat and cool the air coming into the unit, leading to a low differential.
  • Blocked or Closed Vents:
    Dirty or restricted vents can cause restricted airflow from the air handler, causing uneven cooling and leading to a high or low temperature difference.
  • Dirty Air Filters:
    A dirty air filter blocks airflow over the evaporator coil, cooling the air for longer and causing a higher differential temperature of the air coming out of your AC.
  • Ductwork Issues:
    Poor quality ductwork can impede airflow, meaning the HVAC system doesn’t cool properly. It can cause a high or low differential and even make it blow warm air.
  • Under or Oversized Unit:
    If your AC is too big or small for the space, it can lead to short cycling, impacting the differential between your supply and return vents.
  • Insufficient Insulation:
    Lack of insulation can lead to more heat energy gain in the indoor air. This can strain your AC and cause it to short cycle, impacting the differential temperatures.
  • Lack of HVAC System Maintenance:
    Over time, an HVAC system can develop leaks, clogs, refrigerant issues, and even damaged components. Without proper maintenance, these issues can impact your differential.
HVAC Technician

TL;DR: Both too high and too low a temperature differential is bad for your AC. High temperature differential means its cooling more than necessary which can increase bills. A low temperature differential means the AC is not cooling properly.

Commonly Asked Questions

How Cold Should the Air Be Coming Out Of A Mini-Split?

The cold air blowing from a mini-split should be 15-20°F cooler than the temperature set on the thermostat.

What Temperature To Set Air Conditioner in Summer?

The ideal summer thermostat temperature is 70-80°F, but it’s advisable to set lower temperatures for rooms more exposed to the sun as they will regain heat quickly.

What Should AC Be Set to at Celsius?

This depends on personal heat preference, but setting your AC to 22-24°C balances efficiency with personal comfort.

Which AC Temperature is Best For Lowering Your Electricity Bill?

The higher the temperature setting, the less you will spend on electricity to power your AC. I recommend setting your AC to 78-80 degrees as it balances efficiency and comfort and can be up to 20% cheaper than setting it to 72 degrees.


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Josh Mitchell


Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

My Favorite Home Appliance?

Midea U Shaped Window Air Conditioner

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