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Community and Q&A

Filter for ERV intake

DCcontrarian | Posted in Green Products and Materials on

I have a whole-house ducted ERV with balanced returns. In my workshop I do some woodworking, and while I try to control the sawdust it does create a fair bit of dust. I would like to put a filter on the return in that room so that I don’t introduce dust into the rest of the system.

The return vent in the room is 4×10 and runs into a 4″ round vent. I’ve been trying to find a vent grill that incorporates a filter, but everything seems to be for the return for an HVAC system and is much bigger. Even finding filters that small has been a challenge. On Amazon I could get a filter grill as small as 6×6, but I’d have to change the boot and I can’t find one that size. I also can’t find filters that would fit it. Plus it would mean patching the drywall.

So is there such thing as a 4×10 filter grill, and a filter that goes with it? I’m just fishing for suggestions.

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  1. PAHighEffBldg | | #1

    This may not help you, but since you mentioned it feeds into a round duct, these are the filters that are used in each of the return air registers in the Zehnder ERV line. They are washable, should be checked frequently.
    Maybe spark some ideas!

  2. DennisWood | | #2

    A small filter will be degraded very quickly with sawdust in play. I’d be very tempted to construct a box cover that could contain a much larger filter, like the Filtrete 1900 in 20x20 size.

    If you’re not doing dust collection at the tools, I’d take a good look at that as well. I’m using a 2 1/2 system with a dust deputy/shop vac combination that works extremely well with the smaller tools.

  3. Expert Member
    Akos | | #3

    I had no luck finding anything outside of the standard floor register filters which have almost no surface area or the filter sock from Zahnder.

    This is my DIY solution from a piece of washable filter material bent into U shape in the back of the register. The weather stripping around the perimeter is for a better seal to the register boot which is needed as these are very leaky. This works pretty well for house dust but I can't see it holding up for wood.

    For a wood shop, I would cut open the wall an install a larger boot and a proper filter grill that takes a standard pleated filter you can buy at a box store.

  4. Expert Member
    DCcontrarian | | #4

    Thanks for the input, it's actually helpful to know that there's not an obvious solution I'm missing.

    So this is what I'm thinking: it seems like the smallest MERV filter I can readily get is 10x10, I can also get a filter grill in that size (like this one: . I can make a 10x10 box using 3-1/4x10 rectangular duct and cutting out one side. If I put a 3-1/4x10 to 4" round stack boot on that I can connect to the existing duct. It will all fit in the stud bay and I just have to make the existing hole in the drywall bigger.


    1. Expert Member
      Akos | | #8

      That sounds like a solid plan. There are some exhaust boxes for commercial HVAC but they won't fit into a 2x4 wall:

  5. DennisWood | | #5

    If you're using a 10x10, try and find one either 2" wide or 4" wide as it will flow a lot better, and require fewer changes.

    Are you using any kind of shop dust collection?

    1. Expert Member
      DCcontrarian | | #6

      I have good shop dust collection and an air cleaner. I just don't want to get dust into the ERV and it's impossible to collect everything.

    2. Expert Member
      DCcontrarian | | #7

      It's only 20 cfm, I think a 10x10x1 will be fine.

  6. kbentley57 | | #9


    It may not be the most HVAC kosher, but you do work in a wood shop, why no just fab up the box you need out of some smooth plywood for the size and chamber volume you need? You could always look into sizing it for a large truck's air filter, from WIX and the like that already have the 'snow guard' or large foam pre-filter applied.

    1. Expert Member
      DCcontrarian | | #10

      That's an interesting idea. Instead of messing with the ductwork I could just take off the grill that's there and put a 10x10x1 box over the drywall. It would have a 4x10 hole in the back that the air exits out of. I could make the box out of wood since it's not buried in the wall. I could probably just use 1x2.

      I also found a 6x10x1 filter box on Amazon and I can get MERV filters to fit it.

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