Calculate heat recovery, supply air temperature, and annual energy savings from airflow, temperature difference, efficiency, and energy cost.

Use the entering indoor–outdoor temperature difference.

Sensible heat only, using standard-air density and balanced flow. Gross savings exclude fan energy, frost protection, bypass and humidity effects.

Illustrative efficiencies only. Enter the manufacturer’s rated sensible value for your conditions.

Use the magnitude before heat recovery, not the temperature rise after recovery.

Heat Recovery Formula

The following formula estimates sensible heat recovery for balanced airflow at standard-air conditions. The 1.08 factor is approximate; humidity, altitude, frost protection, bypass and fan energy are not included.

HR = 1.08 × Q × dT × E / 100

Variables:

  • HR is the Heat Recovery (BTU/h)
  • Q is the airflow rate (CFM) 
  • dT is the entering indoor–outdoor temperature difference before heat recovery (°F) 
  • E is the heat recovery efficiency (%) 

How to Calculate Heat Recovery?

The following steps outline how to calculate the Heat Recovery.

  1. First, determine the airflow rate (CFM).
  2. Next, determine the entering indoor–outdoor temperature difference before heat recovery (°F). 
  3. Next, determine the heat recovery efficiency (%). 
  4. Next, gather the formula from above = HR = 1.08 * Q * dT * E/100.
  5. Finally, calculate the Heat Recovery.
  6. After inserting the variables and calculating the result, check your answer with the calculator above. 

Example Problem:

Use the following variables as an example problem to test your knowledge.

airflow rate (CFM) = 100

entering indoor–outdoor temperature difference before heat recovery (°F) = 30

heat recovery efficiency (%) = 50

HR = 1.08 * Q * dT * E/100 =  ?