Noise level is a good indicator of balanced air flow to HVAC registers.

 I take exception to the Google AI search result of the title of this blog post.  Here is that search result as formatted into a My Google Document.

While noise level can be an indicator of airflow issues, it is not a reliable primary tool for achieving a precisely balanced HVAC system. Noise typically signals imbalances or restrictions rather than balance itself. 

Why Noise Level is an Incomplete Indicator

• Presence of Noise: Unusual or loud sounds—such as whistling, rattling, or a "whooshing" like an airplane—often indicate excessive velocity, restricted airflow from a dirty filter, or undersized ductwork.

• Absence of Noise: A quiet system generally suggests healthy performance, but it does not guarantee that every room is receiving its designed volume of air (CFM).

• Ambiguity: Different mechanical issues, such as loose components or failing motors, can produce noise that mimics airflow problems, making it difficult to diagnose balance by ear alone. 

Reliable Indicators and Tools for Balancing 

Professional air balancing relies on measurable data rather than sound quality: 

• Flow Hoods (Balancing Hoods): These capture air directly from a register to measure the exact volume of air (CFM) entering a room.

• Anemometers: Used to measure the velocity of air moving through the ducts or exiting vents.

• Manometers: Measure static pressure differences to identify blockages or leaks that affect distribution.

• Thermometers: Track temperature splits across different rooms to identify "hot" or "cold" spots caused by poor balance. 

In summary, while a balanced system should operate quietly, achieving that balance requires adjusting manual dampers based on specific pressure and volume measurements rather than just listening for noise. 

Are you experiencing specific noises like whistling or rattling at your vents, or are you trying to fix uneven temperatures between rooms?

Here are my complaints with this contradiction of my positive statement.

• Every damper I have seen in residence HVAC has been unknown to home occupants, set full-open but yet acting as a large flow resistance. I have made the discovery in a complete demolition of unprofessional ducts, with foolish resort to D-boxes having hacked-in unguided flow through sharp-edged duct starters of Medusa paths to individual registers.
• Even same-velocity at all open registers is achievable by thoughtful, sure other means. Occupant regulation of HVAC is intuitive only in the register-damper closure for economy at a room not occupied.