ERV/HRV Balance Calculator
Supply/exhaust airflow balance for a heat/energy recovery ventilator.
Enter your values
ⓘ Live results
Results
- Imbalance
- 10%
- Net pressure tendency
- Slightly negative
- Within 10% tolerance?
- Yes
- Average airflow
- 100 CFM
Quick answer
Balanced ventilation systems should have supply and exhaust CFM within about 10% of each other to avoid pressurizing the home.
Imbalance % = |supply - exhaust| / average x 100
How to use the ERV/HRV Balance Calculator
- 1Measure supply and exhaust airflow with a balometer or flow hood at each register.
- 2Total each side and compute the percentage imbalance.
- 3Adjust dampers or fan speeds until within about 10%.
Worked example
Using the values the calculator loads with:
Inputs
- Measured supply airflow95 CFM
- Measured exhaust airflow105 CFM
Results
- Imbalance10%
- Net pressure tendencySlightly negative
- Within 10% tolerance?Yes
- Average airflow100 CFM
Frequently asked questions
Is some imbalance ever intentional?
Yes — some codes call for a small negative bias to reduce moisture intrusion into wall cavities.
What causes drift over time?
Dirty filters or clogged cores slow one airstream more than the other, so recheck balance annually.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.