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Decentralized ductless ventilation system: Zehnder, TwinFresh, or Lunos?

user-6990904 | Posted in General Questions on


Background…We are building a 2000 sq ft home at 7000 ft in Colorado, climate zone 6b, with about 7000 HDD. The house will be tight but we are NOT going for any certification. It is one story, 3 bed, 2.5 bath. My spouse has lots of allergies and is opposed to duct work. As we live with doors and windows open a fair amount of the year he is opposed to adding ductwork in the house for an HRV OR ERV. Whether that makes sense is NOT the question.

Question.. apparently several companies make decentralized ductless ventilation systems. Martin wrote two years ago about Zehnder, and also mentioned Lunos and TwinFresh. Any opinions or experience about these or others would be appreciated.

Likely there is relevant info you need to answer this question, just not sure how much to bore you with.

Thanks in advance from a building newbie, be kind please,


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  1. GBA Editor
  2. user-6990904 | | #2


    Thanks for the answer and review with links, as I missed the Lunos articles, but read the Zehnder. I think we will likely pick one, and appreciate your mention of the noise level as another feature to be attentive to.

    Again, thanks, lydia

  3. user-7005079 | | #3

    Hello Lydia,

    I am also in the process of building a house in Colorado (similar specs as yours) and are leaning towards the Lunos options. Keep us posted as to how you progress...


  4. user-6990904 | | #4


    In a separate post, Kevin Dickson wrote a piece on ductless decentralized ERV/HRV. I reached out to him. He is apparently in Colorado and involved the green building/net energy. Anyway I emailed him and he responded that he installed a twin fresh and is very happy with its function and quietness. Not sure if that helps.

    We will likely go with either Lunos or Twin Fresh, installing two in the house, mostly for winter use or when we are away. Otherwise we sort of live with open doors/windows.


  5. user-6990904 | | #5


    Here is the link for Kevin Dickson’s blog. I don’t know him, but found the info on this site and his helpful. ESP for,Colorado


  6. Debra_Ann | | #6

    If you just want fresh air, and you're not concerned with having an ERV or HRV, then you might look into the Air King QuFresh air intake fan. Variable speed options (40-120 cfm), and an option of using a filter between MERV 6-13. Can regulate intake based on temp or humidity levels. Will soon have another option for a tiny ceramic heater core to preheat incoming air during severe cold.

    I like the concept of the more affordable Twin Fresh, though I am concerned with the manufacturer being small and overseas.

  7. Expert Member


    Doesn't the Qufresh need ducts? It looks more like the in-line fans Panasonic and others make that an alternative to the ductless Lunos or Twin fresh

  8. Debra_Ann | | #8

    It can be a very short straight metal duct. We're tentatively planning on installing a Qufresh inside a closet - bringing air in through an outside wall, and out into the room at the other end of the closet. I don't want any ductwork that I can't easily clean myself, when necessary. I really like the MERV 13 filter that it can handle. And I like the variable speed fan it has.

    My ventilation exhaust fan (also variable speed) is in my crawl space, because it is required for our closed conditioned crawl without HVAC ductwork. So our fresh air is coming in at one end of our ranch, into the large main room of our house when it will be conditioned (heated, cooled, dehumidified).

    Then it's being drawn through the length of our house, then down into vents into the crawl, then across the length of the crawl space, and out the other end. I can adjust the rates of the two fans so that our house can have positive, negative, or balanced pressure.

    One of the challenges of not having ductwork is distributing fresh air throughout the house. I'm hoping our ventilation plan will help with that.

    I'd really like to use a Lunos or Twin Fresh in my bedroom, but it would draw in a lot of humid air into a room that doesn't have any way to condition it. So the fresh air will be introduced near our mini split in our main room, before it's drawn into our bedrooms.

  9. user-6990904 | | #9


    You have thought this through, impressive. I am the original poster and know very little. Thanks for another option.


  10. PAUL KUENN | | #10

    Good day Lydia!

    We love our Lunos. Very easy to install in about any depth wall. Very quiet. Our 1200 Sq. Ft. well insulated and tight (less than 1 ACH) house uses one pair and we now have no humidity problems in our cold and damp climate near Green Bay, WI. They use about 13 watts total and run at about 30cfm at full speed but we use the medium setting at 20 cfm. There's only two of us and we're only around in the evenings after work but have lots of plants and small trees (norfolk, lemon & lime) growing inside. At 20 below zero they use no external heat source and do not frost up even when we have high humidity off the big lake at those below zero temps. Proof is in the pudding.

  11. Debra_Ann | | #11

    Lydia, choices for ventilation can vary depending on climate. I believe your climate is probably drier than mine year-round, which I think gives you more options. If I leave my windows open all summer, everything inside gets very damp, as our outdoor dew point is so high. Paper wilts, and my sheets feel damp when I crawl into bed. But I don't have that problem with ventilation in the winter, because the dew point is very low then - even if the outdoor humidity is fairly high.

    I remember being shocked when I camped in the desert one year - wet wash cloths hung out at sunset would be bone dry come dawn! That would never happen here in Virginia.

  12. Jon_R | | #12

    Be careful with CFM requirements. 15 CFM of "clean" outdoor air into a closed door bedroom provides much more dilution of indoor air pollutants than 15 CFM of "dirty" air that has already traveled through much of the house.

  13. Expert Member
    MALCOLM TAYLOR | | #13

    To Jon's point: I don't know about what other codes require, but under ours fresh air must be supplied directly to bedrooms, and exhausted from the kitchen and living spaces.

  14. Debra_Ann | | #14

    Good points, Jon and Malcolm. I haven't found anything in our code requiring fresh air directly into bedrooms, but I'll ask my building inspector. That might be a requirement for ducted ERVs/HRVs. We are allowed to just use a bathroom fan for whole house ventilation (exhaust only), and that wouldn't control where air entered the house at all. To better control air quality, I prefer to slightly pressurize our house instead and filter the incoming air well.

    I would prefer fresh air directly in my bedroom, but our summer humidity is so high that it wouldn't be comfortable. In the winter, I could just crack my window open, if necessary. I plan to monitor the CO2 levels in my bedroom, and to reduce VOCs and other contaminants in the house as much as possible.

  15. Jon_R | | #15

    Debra, if you can leave the bedroom door open, then there will be so much airflow that air quality and humidity and probably temperature will be fine.

  16. Expert Member
    MALCOLM TAYLOR | | #16


    Possible code concerns aside, your approach sounds like a good idea in your climate.

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