What should the temperature difference be between AC supply and return?

Author: Brenda Sipes IV  |  Last update: Sunday, October 19, 2025

Ideally, there should be a temperature differential of around 14° to 20° Fahrenheit between the incoming air and the air being blown out by your air conditioner. This means that if the air entering the system is 75°F, the air coming out of the vent should be between 55°F and 61°F.

What should the temperature difference be between flow and return?

Most gas boilers are set up to operate at what is called 80/60 flow and return temperatures. This means the boiler heats up the water (called 'the flow') to 80°C. The water returns to the boiler after travelling around all your radiators (called 'the return') at 60°C, having given off 20°C to the room.

What is the temperature of supply air and return air?

Whereas the supply air temperature provides information about whether the refrigeration unit is working, the return air temperature allows conclusions to be drawn about the temperature of the cargo. The prerequisite for this is that the air actually flows through the cargo and takes on the temperature of the cargo.

What should an AC temperature differential be?

However, it's best to have a 16 to 22°F difference between your supply air and return air temperature when you set your thermostat. HVAC professionals call this the “evaporator Delta T.” When a temperature difference is within the Delta T, your AC is working properly.

Should return air be equal to supply?

Yes. Your air supply should be balanced. The return and supply ducts need to maintain that balance, and this only occurs because an equal amount of air should be entering and leaving your HVAC system.

" Supply vs Return: What Your Air Conditioning Delta T says About System Performance"

What temp should return vs supply be?

While there isn't any perfect temperature you should set your HVAC system to, there is an ideal temperature difference between the supply and return air, which should be between 16 and 22 degrees Fahrenheit. This difference in temperature is the evaporator Delta T.

What are the symptoms of not enough return air?

Symptoms include weak airflow and uneven cooling or heating throughout your home, with some rooms feeling much cooler or warmer than others. Homeowners should regularly check vents for consistent airflow. If you notice a significant drop in air pressure or uneven temperatures, it could indicate return air issues.

How cool should my house be if it's 100 outside?

For many of us, 70 degrees is the ideal indoor temperature, but when it is close to 100 degrees outside, your AC unit will be working quite hard to meet these expectations. Consider setting your thermostat at 75 degrees to 80 degrees in your home if the outside temperature is approaching triple digits.

What should I set my temperature differential to?

A common range that aids with excessive cycling and cooling/comfort control is a differential set anywhere between 0.8-2 degrees for cooling and between 0.5-1 degrees for heating cycles.

How far should the thermostat be from the return?

In general, placing your thermostat at least five feet away from things that create air flow (including air returns, heating vents and even drafty windows) can help you maintain a more constant temperature and lower energy costs.

What should AC supply temperature be?

Now, from the example above, with 75 degree air being pulled in at the air filter, what temperature should we expect to be blowing out? Well, the general consensus is somewhere between 14 to 20 degrees colder than the intake temperature. From my example, 55 to 61 degrees would be an acceptable range.

How to tell if a unit is overcharged?

Below, you will find common symptoms that an overcharged air conditioner presents:
  1. Elevated Heat Discharge.
  2. Increasing Energy Bills.
  3. Frozen Air Conditioning Coils.
  4. Noisy Air Conditioner Compressor.
  5. Sudden Cooling System Shutdown.
  6. Uneven Air Conditioner Pressure Levels.
  7. Conclusion.

What is the temperature difference between supply air and room air?

The typical supply air temperature difference compared to the room air temperature in the cooling mode is as follows: 8°C–12°C in mixing ventilation with ceiling diffusers; 3°C–5°C in displacement ventilation and UFAD system (comfort applications); 4°C–10°C in displacement ventilation (industrial applications);

What is a good return air temperature?

Ideally, there should be a temperature differential of around 14° to 20° Fahrenheit between the incoming air and the air being blown out by your air conditioner. This means that if the air entering the system is 75°F, the air coming out of the vent should be between 55°F and 61°F.

What should my flow temperature be?

So, what is the optimal flow temperature? Generally, your boiler's flow temperature should be between 60°C and 70°C. If you were to set it to a higher temperature, it runs the risk of scalding with the water being too hot for use. Beyond that, it would make your boiler less efficient.

Should the thermostat be on the flow or return?

Most modern thermostatic radiator valves are bi-directional – so can be fitted on either the flow or return pipe of your radiator. However, it's always best practice to fit the TRV on the flow pipe that enters your radiator.

How cold should air be coming out of an AC vent?

If the AC system is operating correctly, then the air coming out of your vent should be about twenty degrees cooler than the regular temperature inside. So, if you're cooling it and the house is 80 degrees, then you would ideally want the air to be about 60 degrees. Have more air conditioner questions?

How long should an AC run to drop 1 degree?

On average, an air conditioner running in good condition should take about 15-20 minutes to drop the temperature by 1 degree in a standard-sized room. However, factors like outside temperature, unit size, and insulation quality can affect this timing.

What is normal differential temperature?

Once broken in, the normal operating temperature for a differential for vehicle in stock trim and regular diving is 170° to 220°. Normal operating temperature on vehicles with large tires, undersized differentials, or while towing is 200° to 250°.

How cool should my house be if it's 110 outside in summer?

Just because the outdoor temperature is above 100, the Ideal temperature to set your AC unit to doesn't change — it's 78 degrees. Higher temperatures in the home are to be expected when the weather is hotter than usual, but your thermostat can still be set the same as if it were a lower temperature outside.

How long should it take to cool a house from 80 to 72?

Cooling a house from 80 to 72 degrees is a common goal for many, especially during the peak of summer. On average, this process takes roughly two and a half to three and a half hours.

How much lower should AC be than outside temperature?

Simply put, it means you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Why not? Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures.

How to increase return air flow?

By installing more return vents throughout your home, they can trap the air and remove it, improving air circulation. A drawback with this method is that your ductwork needs enough space to support additional vents. Smaller homes that can't add more vents need to pursue other options.

How to tell if return air is working?

Because the return air vent works to suck air from a room and back into the ducts, you can try this simple test to see if it is working: take a tissue or thin paper and hold it in front of the return air vent, about 6” away. If the paper is being pulled toward the vent, you know it is doing its main duty.

How to tell if air return is too small?

Symptoms of an Undersized Return Air Duct
  1. Parts of Your Home Are Hotter or Colder. ...
  2. More Air Is Blowing In Rooms Near the AC Unit. ...
  3. Air Pressure Differences from Room to Room. ...
  4. You Don't Feel Enough Return Air. ...
  5. Air Ducts Are Leaking. ...
  6. Increased Need for Repairs. ...
  7. Don't Rule Out Other Problems.

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