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Any problem with this plan for a retrofit HRV after blower door test?

David Schreiber | Posted in Mechanicals on

Building a new trac home in Syracuse NY. The builder is obligated to meet the 7ACH standard in the previous (?) code. At that level of leakiness a house probably doesn’t need any kind of ventilation.

I have spent the last 3 weekends at the house foaming and sealing every nook and cranny that I could find. I am starting to think that the house may be tight enough that it needs active ventilation.

Some details: fiberglass insulation, builder grade windows, lots of air sealing, 1200 cfm range hood fan over an indoor grill, 3000 sqft ranch including 1000 sqft in the basement, max of 4 occupants and 4 bathrooms, one with a 250(?) cfm fan. Hi efficiency, 2 stage gas forced air furnace.

After closing my plan would be to have a blower door test done and decide whether I need ventilation. I had an HRV in my last home and think I could buy one on line and do the installation my self.

2 questions: What reading on a blower door test would indicate the need for mechanical ventilation? Given my situation, would an HRV be the way to go or are there other options? Cost is obviously a concern and DIY friendly would be a plus.

Thanks

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    David,
    It is a code violation to install a 1,200 cfm range hood fan unless you also install a makeup air unit. I hope your builder understands that. Such a range hood fan can cause serious depressurization and backdrafting problems, especially if you have an atmospherically vented water heater, a fireplace, or a wood stove. For more information, see Makeup Air for Range Hoods.

    If you are doing your best to seal your home's air leaks, and are striving to make your thermal envelope as airtight as you can, then you definitely need a mechanical ventilation system. This article explains all of your options: Designing a Good Ventilation System.

  2. David Schreiber | | #2

    Thanks Martin

    I have read that article and many of the others that it links to but a lot of it is over my head. I will re-read it but can you speak to what result on the blower door test would indicate that I need mechanical ventilation? I am hoping the house is tight enough to require it but if it's not and it's leaky already ... then there's no point.

    Assuming that the house is tight enough to require mechanical ventilation can you recommend a strategy that would work given my needs?

    And finally, my building permit was issued prior to October 2016 so my understanding is that we are under the previous code and that no make up air is required by code. My plan on this is to close on the house, do the blower door test, see how the house feels and then decide what kind of ventilation including MUA is necessary. Unfortunately I have no confidence that my builder can figure any of this out and I dont want to pay him to implement a solution that does not meet my needs. The furnace, gas fire place and hot water heater all have their own supply for combustion air so I assume that we are not going to create an unsafe situation in the few weeks or months that it takes me to figure out what I need and implement it. Does that sound right?

    Thanks

  3. Jon R | | #3

    > see how the house feels and then decide what kind of ventilation

    I suggest that some of harmful things that ventilation removes are undetectable without instruments. And that blower door results do not correlate well to the natural ventilation rate at any given time. So continue to air seal and install a HRV.

  4. Charlie Sullivan | | #4

    What stage of completion is the house in? I am wondering whether there are things to do now before it's too late.

  5. David Schreiber | | #5

    "What stage of completion is the house in? I am wondering whether there are things to do now before it's too late."

    The house is at the sheetrock stage. However the rangehood and furnace are not installed yet. They have not done the siding yet and I was thinking that I might pick up two wall caps and have the siding guys install them. This way if I do an HRV at least the penetration to outside is there.

  6. GBA Editor
    Martin Holladay | | #6

    David,
    Two commenters (me and Jon R) have advised you to install a ventilation system. Depending on leaks for fresh air isn't wise.

    If you have come this far, and you care about this issue, you want to seal all the leaks you can find. If you intend to hire a blower-door contractor to perform a test, tell the contractor that you want to perform blower-door-directed air sealing. Be prepared with spray foam, tape, and caulk to address the leaks that the blower door reveals. Tell the blower-door contractor to schedule enough time for some air sealing work.

    If the article on GBA titled "Designing a Good Ventilation System" is over your head, then you need to hire a mechanical engineer to help you design your ventilation system.

  7. Charlie Sullivan | | #7

    If it's at a stage where adding ducts for HRV is difficult, a ductless HRV, from Lunos or Vents-us, might be attractive.

  8. David Schreiber | | #8

    "If it's at a stage where adding ducts for HRV is difficult, a ductless HRV, from Lunos or Vents-us, might be attractive."

    If I do it I would tap into the existing return trunk and rely on existing duct work to move the air.

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