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Community and Q&A

Where to Locate the ERV Intake

chrisjstelzer | Posted in Mechanicals on

Hey Everyone,

I’m having a heck of a time finding a suitable location for my ERV intake.

Exhaust is not a problem, I’ll be going through the roof.

Intake is another story…

My house is a townhome, built in 2020.

I am hooping to mount the ERV inside of my laundry room on the second story of my house, which is a conditioned space. From here, I’ll run ducting through the drywall, up into the attic.

Ducting will supply fresh air to all 3 bedrooms located on the same floor and there will be one exhaust extracting from the central hallway.

I cannot access an exterior wall from inside my attic. I have 9 foot ceilings.

The only option I can think of for fresh air supply is some type of soffit vent intake to supply the ERV with fresh air.

I have read on this website and others that fresh air intake on an asphalt shingle roof is not good, and I agree.

In the attic I have rafter baffles near the end of the roof to keep the blown-in insulation in place, while venting the attic.

However, behind the rafter baffles there is 2 x wood material or “Blocking”. Meaning I cannot readily access the flat soffit area where I was planning to put my fresh air intake.

So my questions to you are:

1. Can I cut a hole or remove this blocking so I can put in my ducting for a fresh air intake?

2. What other options can you think of for a fresh air intake for my ERV?

I’m really at a loss and my next option is to consider a Lunos HRV that will go through the exterior wall, but these have limited CFMs and the VOCs in my new construction townhome are very high, above 1,000 PPB regularly.

Thank you!

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  1. Expert Member
    Michael Maines | | #1

    I would duct the intake straight through the wall. If you don't like the looks of exposed ductwork you can wrap it with framing and drywall.

    If for some reason you don't want to go through the wall, unless local codes such as fire codes or seismic codes prohibit it, I don't see any reason you couldn't cut neatly through the truss blocking. It's there mostly to keep the trusses upright but as long as the adjacent ones stay intact you should be fine. 90° bends reduce air flow so going straight through the wall is preferable.

  2. C L | | #2

    In a similar situation, I did exactly what you are proposing.
    Since the top of the insulation is higher than the top of the attic floor framing, I went in with some 2x's perpendicular to, and straddling two joist bays, to raise the top of the framing, and then put some sheathing over that for access. Just worked my way out.
    Used a Panasonic EZ Vent as the soffit intake but removed the white flap damper (the EZ vent is, I suppose, meant to be used for exhaust only). I cut a piece of screen material and inserted that between the exterior grill and the body of the EZ Vent to keep insects out. Even though the EZ vent is rated for 4" duct, it has more si of free area than other 6" soffit systems, so I used it.

    One thing to consider before you go to this trouble is whether totally airing out the house for awhile might solve your VOC issue, and/or trying to identify the specific source of your high VOC's and deal with that in lieu of this ERV. After all, even with an ERV, the VOC's will still be there, you will just be moving them out quicker. Best to try to get rid of them. If it is a particular item, such as flooring, certain trim, etc. it may be better to just replace that.
    Also, do you know how tight your house is? If it is not really tight, an ERV may not help much with the VOC's.

    1. chrisjstelzer | | #3

      Thanks for your reply CL.

      I am planning on 6'' , flexible and insulated ducting for my install.

      Were you able to connect the 6 inch ducting to the 4'' Panasonic EZ Vent?

      1. C L | | #5

        Sorry - just saw this.
        My connection of the 6" ducting to the 4" EZ vent is unconventional.

        I needed a 6" soffit damper for the 6" kitchen exhaust hood, so I bought a 6" dampered soffit exhaust at Lowe's:
        This soffit vent can be used to vent 4", 5" or 6" - you snap off extension rings to make it fit larger pipe. So I snapped the 4" collar off to fit a 6" kitchen exhaust duct.

        When I got around to trimming out the 6" makeup air duct, I realized the 4" Panasonic EZ vent has more free area than the 6" Imperial vent linked above. So I used the EZ Vent, but needed to transition from the 4" EZ vent to the 6" duct. The 4-6 transitions I found in the store were too long for the area I had to work with. I used the leftover 4" to 6" collar from the kitchen exhaust vent and it worked perfectly.

        All that said, my 6" duct connected to the Panasonic EZ vent is for kitchen exhaust makeup air. I removed the damper from the Panasonic EZ vent so it would work for makeup (intake) air.

        I also have the Panasonic EZ vent as my ERV exhaust termination, but my ERV's are ducted with 4" so the EZ vent works perfectly.

        1. chrisjstelzer | | #6

          Thanks for the reply CL. That is quite helpful!

    2. qofmiwok | | #4

      I believe the consensus on this now is that would be a losing battle. There are so many chemicals in everything you buy it would be very difficult to keep them all out. Not to mention needing it just for air if it's a tight house.

  3. Expert Member
    Josh Salinger | | #7

    One thing to pay attention to is the need to regularly clean the intake of the ERV. They get clogged with cottonwood fluff, pollen, bugs, etc. etc. Being up on the eave of a second story isn't convenient. Not that it makes your problem any easier, but one could consider running the duct down through the second story floor system and out the wall at the rim joist or even below that. On a recent retrofit project where the intake was on the second story we discovered that the screening was completely clogged and the machine had been doing essentially nothing but using electricity for who knows how long. On the other hand, I have a friend who keeps a rechargeable vac near his intake and cleans it fairly often as it was deliberately located near his front door. Just another wrinkle to throw at you...

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