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HVAC Multifloor return system – Should I get grills with dampers to control velocity?

jberks | Posted in Mechanicals on

I am designing the new HVAC system for my home. I plan to do a 4 zone system, lennox SLP98UH090XV60C

Attached is a diagram for a visual.

I am getting into the return ductwork. To my understanding it’s good practice is to have a return grill on each floor and it will better circulate air. Also, I separated them into two zones to help with noise transfer between floors.

However, this begs the question, as the air handler blower kicks in, would it suck more from the closer grills and less from the further grills. IE: will I get lots of air movement and suction (and possible noise issues) from the basement and first floor returns, and less so on the 2nd and 3rd floor?

So I was trying to think of a good solution to control this, I was thinking of getting return grills with integrated dampers, to which I could take an Anemometer in front of each grill and adjust them independently until I get a uniform level of velocity.

What do you think? Is this concern valid or should I not bother?

Example grill with damper:


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  1. GBA Editor
    Martin Holladay | | #1

    I will defer to other, more experienced respondents. But here's my understanding:

    1. Managing airflow in a zoned forced air system is tricky, and often involves compromises. Forced-air systems are tougher to zone than hydronic systems. (This is another argument in favor of ductless minisplits.)

    2. Noise in return air systems is not generally a problem.

    3. Registers have integral dampers; grilles don't have dampers. Return air systems require grilles, not registers.

    4. The way that HVAC system designers assure balanced return air flows is duct design, not the use of dampers. If the return ducts are sized properly, the return air system will pull air from the rooms where the HVAC designer wants the air to come from.

  2. Jon_R | | #2

    Some general advice/goals. Design the heating/AC system such that it doesn't pressurize or depressurize any closed off room or area with respect to the outdoors. Verify with a micromanometer.

    Unless necessary for no heat, don't allow zone dampers (supply and return to stay balanced) to completely close. This will help with the minimum airflow requirement and noise.

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