Mixed Air Temperature Calculator

Calculate the mixed air temperature where outdoor air and return air meet at an AHU, before the coil.

Calculator

Mix by

Units

Outdoor air temperature (°F) Example: 95°F summer outdoor air, or 20°F winter outdoor air.

Return air temperature (°F) Example: 75°F return air from the room.

Outdoor airflow (CFM) Example: 2,000 CFM outdoor air.

Return airflow (CFM) Example: 8,000 CFM return air. Total here is 10,000 CFM.

About this calculator

This mixed air temperature calculator is the dry-bulb mix at the AHU inlet. Humidity stays on the psychrometric tool. Browse the HVAC calculator hub.

Calculation Results

79.0 °F

Outdoor air 20.0% · dry-bulb mix

Formula: MAT = (Flow_OA × T_OA + Flow_RA × T_RA) / total flow

How to use this result

Treat the mixed temperature as the air temperature entering the cooling or heating coil. It is a volume-weighted dry-bulb estimate. It ignores the density difference between hot and cold air, and it does not tell you coil tons or whether the outdoor-air amount meets a ventilation minimum.

Continue Your Calculation

Use this mixed temperature as the coil entering condition, then screen cooling load separately.

Screen cooling load →

Mixed air temperature examples

Volume-weighted dry-bulb. Click a preset above to load the summer or winter case.

Case	Outdoor	Return	OA %	Mixed
Summer AHU	2,000 CFM at 95°F	8,000 CFM at 75°F	20%	79°F
Winter AHU	20°F	70°F	20%	60°F
Equal mix	1,000 CFM at 60°F	1,000 CFM at 80°F	50%	70°F

Mixed air temperature formula

By airflow: MAT = (Flow_OA × T_OA + Flow_RA × T_RA) / (Flow_OA + Flow_RA)

By percent: MAT = T_OA × OA% + T_RA × (1 − OA%)

Outdoor-air percent: OA% = Flow_OA / (Flow_OA + Flow_RA)

Example: 2,000 CFM at 95°F and 8,000 CFM at 75°F. MAT = (2,000 × 95 + 8,000 × 75) / 10,000 = 79°F. Outdoor air is 20%.

Need wet bulb or dew point? Use the psychrometric calculator. Need tons? Use the HVAC capacity calculator. Hub: HVAC calculator.

Which HVAC step this is

Question	Use
Dry-bulb where outdoor and return air mix	This page
Wet bulb, dew point, humidity ratio	Psychrometric calculator
Room or facility cooling tons	HVAC capacity calculator
CFM from room volume and air changes	ACH to CFM

Frequently Asked Questions

How do I calculate mixed air temperature?

Use MAT = (Flow_OA × T_OA + Flow_RA × T_RA) / total flow. Example: 2,000 CFM at 95°F and 8,000 CFM at 75°F gives 79°F.

What is the difference between airflow weighting and outdoor-air percent?

They are the same dry-bulb mix. OA% = outdoor airflow / total airflow. 2,000 CFM outdoor and 8,000 CFM return is 20% outdoor air, and 95 × 0.20 + 75 × 0.80 = 79°F.

Does this mixed air calculator include humidity?

No. This is a volume-weighted dry-bulb. For wet bulb, dew point, or humidity ratio, open the psychrometric calculator.

Where do I use the mixed air temperature?

Use it as the temperature of air entering the coil after outdoor air and return air mix. Screen tons separately with the HVAC capacity calculator.

Does 20% outdoor air mean the ventilation rate is acceptable?

No. The percent is only the mix you entered. This page does not check a ventilation-code minimum.