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Is this too many exterior penetrations for a tight house?

brenton_roubo | Posted in General Questions on

I am building a 2800 sq ft house in Scarborough, Maine (zone 6). I will be insulating soon and I am getting my vents installed now as the siding is being done. My question is, can there be too many penetrations in the exterior wall? I have the following and it seems excessive yet suggested by previous threads. 

(1) 6” vent with for kitchen range hood
(3) 4” vents for (1 for each bath exhaust Fan)
(2) 6” penetrations (exhaust/intake for ERV)
(1) 4” vent for dryer

this just seems like it’s been a waste to make such a tight house if I have so many penetrations. Yes each of these has flaps (except the intake) to try to prevent drafts, but they certainly won’t stop all air. I will obviously see how bad it is when the blower door test is performed, but I Still feel like this is nuts. Any thoughts?

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  1. Expert Member


    Think of it this way: Tightening a house isn't to stop air entering and leaving a house, it's to allow you to decide how much and where the air will be supplied and exhausted. A tight house without the penetrations you list wouldn't be livable. Even houses built to the most exacting standards, like Passive H0use, have all the same vents.

    Do your best sealing the ducts as they exit, and use multiple backdraft preventers if necessary. Even if the air-leakage thr0ugh them is measurable, it isn't a problem the way air-leakage through building assemblies is.

  2. Expert Member
    BILL WICHERS | | #2

    I’d recommend trying to place all the campers / backdraft preventers in serviceable locations. Sometimes these things get stuck, and you don’t want to have to open up a huge amount of your house just to access them.

    Seems to me you have the vents you need. Nothing excessive, just what is required. You’re always going to need SOME ventilation after all — a perfectly sealed house would suffocate you.


  3. Trevor_Lambert | | #3

    It's pretty subjective. The ERV penetrations are non-optional, and they also don't allow any air leakage without heat exchange. I personally would forgo the dryer vent and use a ventless dryer. That is probably your biggest energy penalty. I'd also forgo the bathroom vents and tie them into the ERV. That's how many tight houses are set up, it's how our house is set up and I have never missed the ability to turn a bathroom fan on. We have a boost switch in each bathroom, but they rarely get used.

    We don't have a vent for the range hood, and I regret that decision. The HRV is not able to keep pace with the particles put into the air by the cooktop. Try to get a flapper with a good positive seal for the range hood, if that's even a thing that exists. You'll want to crack a window when you run the range hood.

  4. maine_tyler | | #4

    While those vents all make sense, I think your point:
    "this just seems like it’s been a waste to make such a tight house"

    has some salience in that IF one is pursuing EXTREME levels of air-tightness with the mindset that it's for the sake of energy savings/payback, then ventilation does seemingly make those extreme ACH figures moot.

    There was a thread a while back about whether or not air-sealing is 'mostly BS.' The consensus was that it's certainly not, but that extreme levels of air tightness (such as Passivhaus) are more for envelop resiliency (moisture concerns) vs saving that last little bit of energy.

    Indeed, what would be the point in going from 1 ACH to .1ACH if you then vent a couple orders of magnitudes*(see below response) more via your vent systems. But you also don't want moisture laden air leaking into susceptible assemblies.

    1. Trevor_Lambert | | #5

      I see what you're saying, but I question your numbers. 1ACH50 represents around 400cfm50 for an average sized house. A couple of orders of magnitude more than that would be 40,000cfm. I don't think there's any bathroom fans or residential range hoods capable of producing anywhere near that amount.

      1. maine_tyler | | #7

        Trevor, admittedly I didn't math that one out. You're right that it's unlikely to be 2 orders of magnitude except perhaps in rare and extreme cases (a SUPER tight house with some significant [over] ventilation going on). 1 OOM might not even be commonplace, but I think it could be seen in not terribly uncommon circumstances.

        To make my case, I'll use 0.5ACH50 and convert to 0.03 nat, which for a 2,000 sq.ft. house with 8' high ceilings (16000 cu.ft.) = 480CFH = 8CFM.

        Recommended ventilation levels in same house with 4 occupants (depending on chosen guidelines of course) would be 90CFM. So it's within that 1 order-of-magnitude ballpark.

        I did a calc in the comments of the mentioned 'air-sealing/bs' thread:
        where I estimated that recommended ventilation rates, using the same imaginary house, correlate to (roughly) 5ACH50. I converted from ACHnat to ACH50, which is certainly fraught with uncertainty and inconsistency. And depending on a host of variables—like size of house, height, wind, chosen ventilation rates, etc.— that number could undoubtedly change a lot. Furthermore, energy savings from heat exchangers are ignored in this scenario.

        So certainly none of it is to suggest we shouldn't build tight; only to illustrate that the upper atmosphere of air-tightness might be more for moisture reasons (if anything) than energy-savings.

  5. ssnellings | | #6

    Air sealing is about improvement, not absolutes. I can think of a half dozen penetrations my house has that yours does not - so all things considered you're still doing well!

    Your three bath fan penetrations could be combined into one penetration with some extra work on ducting design and switching to a remote fan unit, that's the only low-hanging fruit I see. I probably wouldn't do it though - it complicates a simple exhaust design in ways I don't find very interesting. Tying them into the ERV like Trevor recommends is a simpler way to accomplish a similar goal.

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