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Community and Q&A

Best location for fresh air intake for ERV/HRV

srivenkat | Posted in GBA Pro Help on

I can’t have the fresh air intake on the wall since it would be quite difficult to drill thru the walls of my ICF home. I do not like the idea of going thru the roof since I do not want risk drawing asphalt shingle gases into my home. One option I am closely looking at is having it on the external soffit pointing down but I see at least one ERV manufacturer advising against it (I wonder why). Does any one see a problem with this approach?

TIA.

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Replies

  1. Richard Beyer | | #1

    There's very little a diamond core bit can not drill through, ICF included. Therefore, your options are not limited aside from location.

  2. GBA Editor
    Martin Holladay | | #2

    Venkat,
    Richard has given you good advice.

    Here is some information from a useful article by Armin Rudd of the Building Science Corporation:

    "Running ventilation ducts through the eave soffit is not recommended. If the outside air intake or exhaust outlet are run through the eave soffit instead of through the sidewall, specific care must be taken to:
    1. not crush the ventilation ducts between the wall top plate and the roof sheathing;
    2. leave the full depth of ceiling insulation in place; and
    3. fully terminate the ducts through the finished soffit to outdoors so that air flow is not restricted and air leakage to/from the attic will not occur."

  3. fitchplate | | #3

    Don't put any air intake/exchange port downhill of radon vent pipes.

  4. srivenkat | | #4

    Thanks for the info and suggestions. I am planning to locate the intake into the generally prevalent winds here on the back/pond-side (ERV in the front garage) of the house, which pretty much constrains me to a soffit intake thru the attic (subject to Armin Rudd's cautions posted by Martin) as the remote wall of windows pond-side is inaccessible.

    Flitch:
    I am going to locate the intake it at least 20 ft away from the Radon vent. I am curious though: doesn't Radon dissipate into the atmosphere (upwards)? Or did you mean to say "downstream wind" from the Radon vent?

    TIA.

  5. GBA Editor
    Martin Holladay | | #5

    Venkat,
    Flitch Plate's opinion that rooftop radon vents are dangerous is a minority viewpoint that is not held by any other radon mitigation expert in the country.

  6. GBA Editor
    Martin Holladay | | #6

    Venkat,
    An ERV should never be located in a garage, because of the danger that garage air will be pulled into the ventilation ducts.

  7. srivenkat | | #7

    Martin,

    The RecoupAerator ERV is supposed to be a totally sealed unit and so the risk seems tiny/minimal, but thanks for the caution.

    BTW, I am planning to have the ERV exhaust stale air into the garage. I am not drawing stale air from the bath rooms into the ERV, so the Garage shouldn't be smelling bad.

    Thanks,

    venkat

  8. JHRockwell | | #8

    What is your climate zone? Assumedly, your garage is outside your thermal envelope. It is poor practice to locate an ERV/HRV outside the building's thermal boundary. Why make the heat exchanger core fight against seasonal climate extremes? Also if your distribution ducts must run the gauntlet from the garage to the conditioned space, concerns arise over air sealing and insulating them, and MOST importantly, fire separation between spaces.

    No ERV is perfectly airtight. Will you store lawn mower near the unit? The possible introduction of deadly pollutants (including odorless, colorless carbon monoxide) is reason enough to re-locate the ERV.

  9. srivenkat | | #9

    Martin and John,

    I think it's getting pretty difficult for me to ignore multiple warnings about locating the ERV in the garage. With some more work I am hoping to be able to locate the ERV in the mechanical room in the basement. I am still constrained to run the fresh air intake via the soffit, attic, garage into the basement mechanical room.

    Any negatives to exhausting stale air simply into the garage instead of extending the exhaust pipe via the garage and attic to the exterior?

    I am in Zone 5A and the garage is outside the thermal envelope.
    TIA.

  10. GBA Editor
    Martin Holladay | | #10

    Venkat,
    Your exhaust duct termination has to be outdoors, not in your garage. If your ERV's exhaust ducts will be pulling stale air from your bathrooms -- and most do -- then building codes require that the exhaust be ducted to the outdoors. Venting to a garage would be a code violation.

  11. Peter Hastings | | #11

    This may be a new topic, if so I apologise in advance. I'm currently planning a house which has, for site reasons, a long E-W axis and very little N-S depth. I was considering the inlet and exhaust arrangements and wondered about the advisability of the following. Run two ducts N-S across the buidling. Fit one duct with a non-return damper at each end which allows air to exhaust and similar dampers in the other duct allowing air in from outside. Irrespective of which way the wind is blowing, air will always tend to be sucked out of the exhaust duct and blown into the inlet duct. Connect the middle of each duct to the appropriate ports on an HRV or ERV and you should be able to reduce (although not eliminate) the need for fans to circulate the air. There would need to be a motorized damper to tame the thing in windy conditions, of course. Comments ?

  12. GBA Editor
    Martin Holladay | | #12

    Peter,
    If your plan is to disable the fans that come with your HRV, then I don't recommend your plan.

    Duct systems have static pressure, and so do the HRV filter and the HRV core. The static pressures are high enough that it will take a fairly stiff wind to overcome the static pressures and deliver much fresh air to your house. That means that your ventilation rate will vary with wind speed.

    On windy days, your house will be overventilated. On still days, your house will be underventilated.

  13. Peter Hastings | | #13

    Martin,
    Thanks for a prompt reply. I was not intending to disable the fans in the HRV, but simply to arrange the ducting to assist them - hence the 'not eliminate' caveat. The motorized damper would be needed to prevent over-ventilation on really windy days.

  14. srivenkat | | #14

    Peter,

    This reminds me somewhat of "Passive HRV" that I read about recently. If you google the term you will see many products including Nu-air (uses the furnace fan) and Ventive solar updraft chimney that does heat exchange but as Martin mentioned some of these may not work all the time.

    venkat

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