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ERV airflow imbalances

ARF9VudJeZ | Posted in Energy Efficiency and Durability on

Hey GBA,

Longtime-no-ask-question-to. I hope you are all well.

Just had a RenewAire ERV (EV450) installed in the new office. The twisting, turning, bending, really-long Fresh Air Supply to the space has a duct run with an equivalent length of around 600′. The straight shot, right-next-to-the-ERV inlet for the Return/Exhaust Air has a duct run with an equivalent length of maybe 80-100′. The ERV serves the individual offices, while we have a dedicated 100% OA unit w/DX cooling that serves the common areas within the space. Common area to office ratio is probably 3:1, in terms of floorspace.

This thing sounds like a freight train, and the system is operating under a significant airflow imbalance: Exhaust Airflow = 930 CFM, Supply Airflow = 610 CFM. (We have some slick Greentrol aifrlow measuring stations mounted in the ducts).

I’m struggling to get my head around what sort of problems would be associated with this type of imbalance from an indoor comfort/IAQ and system performance perspective (rather than an over-exhausting/energy penalty perspective). Can this imbalance cause problems with the core?

I’m in Climate Zone 5A. Any thoughts or opinions?

Thanks a ton.

GBA Prime

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  1. GBA Editor
    Martin Holladay | | #1

    Did the contractor who installed the ERV commission the system? The air flows should have been balanced.

    The simplest way to balance the air flows would be with dampers, although the ERV manufacturer may have another balancing procedure in its installation manual.

    Needless to say, long tortuous ducts introduce static pressure that the fans have to fight against. These problems can be reduced by large ducts with as few fittings as possible. You want long-sweep ells, with as few abrupt changes of direction as possible.

    Note the following sentence from the Guide Specifications provided by Renewaire (
    [Click image to enlarge]

  2. GBA Editor
    Martin Holladay | | #2

    Venmar is better than Renewaire at providing information on HRV balancing. To read the instructions provided by Venmar, see my answer to a previous question on this topic:
    How best to balance an HRV's intake and Exhaust?

  3. ARF9VudJeZ | | #3

    No commissioning report....yet. Still going to hold them to that.

    Any thoughts on the impact that this imbalance might have on IAQ or the longevity of the ERV?

  4. GBA Editor
    Martin Holladay | | #4

    If the ERV is depressurizing your building, you should be sure that any atmospherically vented combustion appliances within the building aren't backdrafting.

  5. user-626934 | | #5


    I'm not surprised to hear the system is out of balance with the ductwork you describe, however, are you sure your airflow measurements are accurate? According to the manufacturer, the EV450 will move 540cfm at 0.25 "w.c. and 338cfm at 1.00" w.c.

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