CSLB C-20 HVAC ContractorVentilation and Air DistributionMedium
A technician finds that one bedroom on a residential system receives noticeably too much airflow while another bedroom receives too little, even though the total system CFM measured at the air handler is correct. What is the appropriate corrective action?
- AReplace the return air grille with a larger unit
- BIncrease the blower motor speed to raise total system CFM
- CAdjust manual balancing dampers located in the branch ducts to redistribute airflow
- DRemove the filter to reduce overall system static pressure
Show answer & explanationAnswer & explanation
Correct answer: C. Adjust manual balancing dampers located in the branch ducts to redistribute airflow
When total airflow is correct but distribution between rooms is unbalanced, the fix is to adjust manual volume (balancing) dampers in the branch ducts feeding each room rather than changing total system airflow.
Why the other options are wrong
- A. Return grille size affects the return side, not supply distribution to specific rooms.
- B. Increasing blower speed changes total CFM, not distribution, and may worsen noise or the imbalance.
- D. Removing the filter is improper and unrelated to fixing room-to-room imbalance.
Branch Duct Balancing
Manual volume dampers in branch ducts allow technicians to redistribute airflow among rooms without changing total system CFM.
- Balancing dampers are adjusted after verifying total system airflow is correct.
- Over-restricting one branch increases flow to others.
- Balancing improves comfort without altering blower speed.
Memory trick: Total is fine, dampers refine.