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How important is the amount of filtration on an ERV?

Alan Afsari | Posted in GBA Pro Help on

How important is filtration on an ERV?


We are building a home in the metro Detroit area (climate zone 5). Last fall, I stumbled across GBA while researching mold in homes on the internet.  I heard an interview of an author Rob Dunn who wrote “Never Home Alone” (which was reviewed by Peter Yost recently  This prompted the question, how do you build a home that is healthy to live in?


I read the book and it prompted my net search on mold, and I came across Martin Holladay’s “Common Sense On Mold”  


Lots of reading and altering our construction plan later, I’m now choosing an ERV and lately I’ve been thinking that filtration must be important – but then I remembered “Never Home Alone”.  The gist of the book is that the inside of homes is an environment and trying to alter it and clean it tends to eliminate most of the non-disease causing germs/bacteria and encourages more disease causing bacteria to thrive. 


Ventilation makes sense to me – fresh air sounds logical.  What should our mind set be on filtration?  Is more filtration better?  Should I choose an ERV that has high filtration (and uses as little energy and has high SRE)?  Maybe fresh air is fresh air and filtering it doesn’t help at all…

Thanks for any responses in advance,


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  1. Expert Member
    Akos | | #1


    In a heating dominated climate, getting high SRE ventilation units are always worth it. The energy savings from ECM blowers pay for the upcharge in a year or two, so it is also a worth it upgrade.

    For the air filtration point of view it depends on what your outdoor air is like. If you are near traffic with high PM2.5 or anybody in the house has pollen allergies, extra filtration is a good thing.

    The air filters that come built in to most ERV/HRVs is pretty small, an external filter box will last longer and cost less in replacment filters.

  2. Charlie Sullivan | | #2

    There are two reasons for filters on ERVs: One is to keep the core from getting dirty, and the other is to clean the air coming into the house. The need for the first function means you definitely want some kind of filter and you want to change it regularly. The need for the second function is as Akos notes, purely determined by how bad the air is outside. In my area, that's almost entirely a function of how many neighbors are using their wood stoves, and how they are operating them. For you, it might be more traffic related. Pollen is easy to filter, as it's relatively big, so even a MERV 7-8 filter will be good enough. It's the fine particulates from vehicles, wood stoves, etc. that require high-performance filters.

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