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Exhaust-Only Ventilation – Latest update based on actual experience or testing?

lifeisgoodsteve | Posted in General Questions on

Hi All,

I’ve read a ton of the articles plus Q&A that address pros and cons of the various ventilation options.  Regarding the exhaust only, my understanding that the commentary from Mr. Nagan’s actual experience with a number of their homes was that the exhaust only was just fine.

Secondly, in other articles the bottom line seemed to be that exhaust only could work fine in small homes with open floorplans and tightness levels that are below PassivHaus.  So…

1.  Are there significant actual experiences or studies done to contradict what Joe Nagan said about exhaust only working fine in his experience in Wisconsin homes he’s seen?

2.  What is considered to be a “small home with open floorplan” in which the exhaust only might work?

A few notes:
– plans attached
– new construction is in Western MT zone 6 (dry climate in general)
– no plans right now for anyone to sleep upstairs fulltime (just guests) and office use in big flex room
– rental apartment above the garage is just there for future build out potential, but will be left unfinished now
– induction stove and electric dryer

There are enough homes and systems out there that I’m not really interested in theory, but rather actual experience and/or tests.



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  1. lifeisgoodsteve | | #1

    ps - Option 2 is to do a very simple ERV with the Intelli-balance 100 and see if can keep it simple enough I could do the install myself.

  2. Expert Member


    In his blog this summer, Doug Horgan wrote:

    "As it happens, I live in a house with exhaust-only ventilation. We use our range hood, have a timer on our bath fan and run it about an hour a day; we have a conventional dryer that blows out 180 cfm whenever it’s running. One of my epiphanies on indoor air quality came when I started using and Awair low-cost IAQ sensor to measure things around my old house, which I figured was leaky enough that there wouldn’t be big issues. So, I was very surprised to see one of my kid’s rooms reading over 2000 ppm of CO2 at night—that’s a very high level that showed we had a serious IAQ issue."

    So theory aside, the main observed problem appears to be closed off rooms at night - which is probably why "an open floor plan" is included as a requirement limiting its use.

    1. lifeisgoodsteve | | #3

      Thanks, I had read that which is a great personal experience and testing reference. It's very nice to see both scenarios tested by him, with the closed doors being a real key.

      "In the parts of the house with open doors and commonly shared air, things were fine; and they were okay in the closed-door areas when the HVAC system was running frequently, but there were many nights when the door was shut, the HVAC didn’t run much, and the air got bad in the bedroom."

      In my case the only time I close the bedroom door at night is if there are guests in the house. Assuming his daughter's room probably had no attached bath where an exhaust fan was and wonder if that would have made a difference? IF I went with exhaust only, I'd have an exhaust fan in my connected master bath where I'd leave the door open always except when in use.

      That said, it's much easier to install ducts now vs. after the fact, so I'm seriously considering my options. It is nice to hear multiple experiences so curious if others have similar experiences or tests.

      1. Expert Member
        MALCOLM TAYLOR | | #4


        Like you I also put a lot of weight on what Joe Nagan says. We use an exhaust-only system sort of by default, as 30 years ago when we built, no one thought much about house ventilation. However, we have the advantage of being able to crack windows year round as our climate is quite temperate.

        Our current building code only allows exhaust-only ventilation on houses under 1800 sf., with no distinctions as to what their layout is. No idea how they arrived at that size. Probably a fairly arbitrary cut off point.

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