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Community and Q&A

HVAC filter MERV ratings vs pressure drop

John Walls | Posted in General Questions on

Heat pump (GSHP)—- system rated for a MERV 11 filter with a 2 speed compressor and motor —–
I want to temporarily (during construction completion) install a filter at the return grille in the ceiling (to keep any potential dust out of the return ducts) in addition to the normal filter at the AHU.
Questions:
1) Are there adverse effects to doing this?
2) What combination of filter MERV ratings could I use so there aren’t any adverse affects?
a) How about MERV 8 at both locations.
b) How about MERV 2 at the ceiling and MERV 8 at the AHU?
3) Is there an algorithm for determining what combination of multiple filter MERV ratings are equivalent to a single filter MERV rating?

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Replies

  1. Tim C | | #1

    MERV and pressure drop are not inherently linked to each other. There is a weak correlation between higher MERV ratings and higher pressure drop, but low MERV filters can have very high pressure drops, and vice versa.

  2. Charlie Sullivan | | #2

    Good idea to take extra precautions to keep it clean during construction.

    If you go to a filter manufacturer that has real engineering specs, they would have pressure drop vs. airflow curves. You could find the pressure drop of the MERV 11 at your flow rate. Then you could find a set of two other filters for which the pressure drops would add up to the same as the MERV 11, and know that you were impeding airflow the same as the MERV 11. But I wouldn't worry too much about getting it just right for short term use during construction.

  3. Robert Hronek | | #3

    Drywall dust is very fine and will pass through the filter. If the u it is running dust will get through. The best best is to seal everything and rely on another source of heat

  4. John Walls | | #4

    Robert,
    Drywall is complete, but not painted yet.
    Should be OK, right?

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