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I had an economizer added to my HVAC system last fall, which is fantastic for cooling my second floor down in the evenings during the shoulder seasons where the weather is cool in the late afternoon through the night and I don't want to pay to run the AC.

However, this is my first spring with it and I have discovered that the MERV 13 filter that is in my HVAC system seems unable to filter out enough pollen to prevent me from having major allergy attacks all night.

Is there a filter system I could install that would be able to handle 800 CFM of outdoor air and filter out the pollen enough that I can breathe?

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  • As @Netduke says, MERV 13 should be more than enough to remove pollen particles, which are actually pretty big. Maybe try a different filter manufacturer? Or supplement with a standalone air purifier?
    – Hank
    May 4 '15 at 17:58
  • MERV 13 only claims to filter 90% of particles of that size, though. May 4 '15 at 17:59
  • Well the ratings are really just categories, not specific guarantees. That's why a different manufacturer may have different performance characteristics. For instance, HEPA makes no guarantees at all about 10 µm particles. Some filters actually do better with smaller particles than larger ones. It's possible that a purpose-built pollen MERV 11 will serve you better than a general-purpose MERV 13.
    – Hank
    May 4 '15 at 18:07
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A MERV 13 filter should not let much if any pollen get through. If you still have pollen getting past, it is likely leaking around the filter.

I would check that the filter is secured tightly in the HVAC system and that there is no place for air to bypass the filter.

To increase filtration of existing plain filters, you can also spray it with a tackifier. The tackifier will catch particles small enough to bounce off the filter fibers but pass between the fibers.

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  • There's definitely no air leaking. Its a track type filter so there's literally no gap on the top and bottom, and the sides compress against semi-rigid foam. However, the internet seems to indicate that MERV 13 does "> 90%" of particles of pollen's size. That seems to me to indicate that potentially 10% could be getting through. During normal operation, air from the house would be exchanged through the filter many times, but in economizer mode the fresh air only gets one pass through the filter. May 4 '15 at 15:39
  • Why not use a HEPA filter? Not enough flow?
    – Netduke
    May 4 '15 at 15:45
  • Yea, I don't think that a standard HVAC blower could handle the pressure drop. May 4 '15 at 15:46
  • One way of increasing filtration with minimal pressure drop is to spray the filter with a tackifier.
    – Netduke
    May 4 '15 at 15:48

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