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Community and Q&A

Choosing Mechanical Ventilation Equipment

chicagofarbs | Posted in General Questions on

Hi All –

If you have followed some of my previous posts, we are pursuing a major exterior retrofit to fix a rehab gone bad by the previous builder/owner.  We will be providing continuous air and insulation layers on the exterior resulting in a much tighter home.  Since enclosure tightness will be improving significantly, we are looking at our options for mechanical ventilation.

In a situation of a full interior rehab, I’d prefer to follow the Passive House design guidelines for a full balanced ERV with kitchen and toilet exhaust connected.  Because we are not gutting the interior, I think it will be difficult to provide a fully ducted system that can capture all the toilet exhausts together effectively.

We do have a closet space that repeats on each level (3 levels total) where we could in theory wall mount a unit and run a vertical chase with small ducts bundled together to supply to each level.  Then run the main exhaust point on the top level, kind of like a whole house ventilation concept.

We have a flat roof, so not a lot of attic space to maneuver in.  3 floors, approx. 1,000 sf per floor.

Alternatively, I was looking at the Lunos product on 475’s website:  While a bit pricey, this would allow us to put in a few individual HRV systems that can be located in the spaces we occupy most frequently (living/kitchen, master bedroom, open rec room in basement).  Has anyone used this product?

I searched the forum a bit for Lunos and it seems most people were considering it in a new construction situation.  Limiting factors seem to be price and that it does not recover as much latent as a true ERV.

Alternatively alternatively, there is the Panasonic individual option:, but it would need to be ceiling mounted.   I do like that it is an ERV, because we are climate zone 5A.  3 of these could do the trick if we locate them well.. maybe in the hallway ceiling adjacent to a bathroom on each level to try and tie in the toilet exhaust?

Has anyone performed this successfully?

Any thoughts/inputs/recommendations are very welcome!


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  1. charlie_sullivan | | #1

    The Lunos products are a good alternative to consider. I haven't personally used them but have heard good things. I considered them for retrofitting my house but needed extensive filtration on the input because of neighbor's smoky wood stoves, which is more practical with a central system.

    If I understand right, the specific panasonic ones you linked don't have defrost, so they need to shut off at low temperature. Some larger Panasonics do have defrost provisions, I think.

    1. chicagofarbs | | #2

      Hi Charlie -

      Good to hear that people seem to like the Lunos. Going to need to look into if the humidity in a Chicago summer could be problematic. We are currently running 2 plug-in dehumidifiers due to our enclosure taking on so much moisture, hoping we can discontinue running those if we tighten up the enclosure and provide mechanical ventilation.

      Good note on the defrost for the Panasonic. I'll have to look more into that.

    2. rondeaunotrondo | | #18

      Lunos now has MERV13 filters (prev 8-9). Still would need better filtration for smoke likely.

      Charlie, you run a Zehnder correct? With HEPA. How’s the smoke?

  2. pjpfeiff | | #3

    I'm using a pair of Lunos in a renovation. In fact...just got them operating a few hours ago. I'm using them in the "attic" we just finished (more of a second story in an old Cape Cod), which I assume it is fairly airtight due to our efforts, whereas the rest of the house is assumed to be pretty leaky. My work-from-home station is in this space and I had noticed the air seeming a little stale so ventilation was probably a good idea. I'd say the air quality seems to be improved, but it's probably a little early to make a call.

    I took some measurements with a high-quality (fast/accurate) cooking thermometer. With outdoor air at 34 deg F and indoor at 71, the end-of-cycle incoming air was 54 deg F (so you can assume the average incoming temp is probably ~62.5 deg). That's on the high setting, which is the only one I've used so far. It can also probably be credited with the few degrees of drop in dew point I've logged. I consider this a good thing right now because I have previously observed moisture on the spray foam against the roof. (I asked a question about that on this forum and the consensus was that what I observed was probably an outlier, but lowering the humidity up hear a bit gives me a little peace of mind). We'll see just how low it goes, though...I may cut back on the ventilation if it starts getting too dry.

    One other thing to note is on a BS and Beer episode someone was saying real-world efficiency of these units is much lower than the claimed efficiency. I want to say they were seeing something like 50% due to wind pressure being not insignificant compared to the fan pressure.

    1. chicagofarbs | | #4

      Hey Paul!

      Thanks for the response.

      Any chance you’re going to track CO2 in that space? I think that would be a good IAQ parameter to track. You could get the Awair Element or similar to track a number of IAQ parameters for pretty cheap.

      I wouldn’t be surprised by the real world lower efficiencies. I’ll try and dig up that BS AND BEER episode. If you have a link handy, please post it !

      1. pjpfeiff | | #7

        Funny you should ask--I was just looking at CO2 sensors. So thanks for the suggestion! I'm still undecided as to whether I will get one or not. But anecdotally, the air definitely feels fresher and my wife said she no longer smells something that I never smelled in the first place.

        The BS and Beer episode is the one on HRVs and ERVs, about 36 minutes in here (but probably worth watching the whole thing):

        1. chicagofarbs | | #8

          I’ve seen a handful of specialists post about this one :

          SAF Aranet4 Home: Wireless Indoor Air Quality Monitor for Home, Office or School [CO2, Temperature, Humidity and More] Portable, Battery Powered, E-Ink Screen, App for Configuration & Data History

          We have the Awair Element and I was given a Kaiterra SenseEdge to test. The Awair is definitely a very nice residential/consumer product that I would recommend.

          Thanks for the BS link, I’m going to watch it when I have some Thanksgiving downtown.

          1. pjpfeiff | | #10

            Any idea what the uncertainties are for the Aranet4? I'd assume similar to Awair, but I can't find the numbers anywhere (and I tend to operate on the rule that if a sensor does not have stated (and believable) uncertainties then I should probably stay away from it).

          2. pjpfeiff | | #11

            All right, I sprung for an Aranet4. Early results are that on the main level (where no one is currently...but where one adult and one child were earlier) the CO2 reading is ~700 ppm and up in the vented space where I spend all day is ~820 ppm. Not sure how much that tells us, but at least CO2 levels seem to be in the acceptable range. I guess I'll try turning the Lunos off for an hour or two and see if anything happens...

          3. chicagofarbs | | #12

            Eagerly standing by for more data !

          4. pjpfeiff | | #16

            All right, not sure I have very useful numbers... But I'd say that when I come into the space (with fans on) the ppm CO2 goes up by ~150 ppm. The short experiment of turning fans off for an hour or two didn't seem to budge the numbers much. Maybe stack effect was still exhausting air through the ERVs? I turned them off but didn't close them. Anyway, I probably need to leave them off for the better part of a day (and close them...and maybe seal off the door to this area?) to get a good baseline. The air quality is subjectively better enough, though, that I don't really want to turn off the vents... In fact having this ventilation makes me want to add balanced ventilation to the rest of the house.

            Also take into account my comments in post #15. The space is bigger than what I think Lunos are meant to treat. It's something like 13000 cu ft of air. The effective volume could be considerably larger accounting for air coming up from downstairs. Or it could be smaller with one knee wall basically closed off, two closets with doors closed, and a space cut out of the bathroom (albeit with the door normally open). None of those spaces are sealed off, but I have to imagine their air isn't mixing in much with the rest of it. Anyway if we go with the 13000 that still means just about 1/11 of the total volume exhausted every hour.

          5. chicagofarbs | | #19

            Thanks for the update, Paul.

            Interesting to hear you wish you installed balanced ventilation for the rest of the house!

            Trying to ventilate existing homes is tough :(

  3. user-5946022 | | #5

    The Panasonic can be wall mounted. Check the spec sheets. The issue is they want both ducts going DOWN when you wall mount it. However, supposedly they have email approving a wall mounted configuration where the ducts go from the unit up to the ceiling.

    1. chicagofarbs | | #9

      Wall mounting 1 unit to serve the entire house makes sense to me.

      Wall mounting 3 individual units, one per floor, is a little bit of a bigger ask, but doable.

      I wonder how difficult (and how much drywall needs to be opened up) it would be to reroute an existing toilet exhaust to the Panasonic and then duct the Panasonic back to the existing exhaust opening the toilet exhaust was originally going through.

  4. Deleted | | #6


  5. PAUL KUENN | | #13

    Hello Scott!
    You have a lot on your slate. I've used Lunos on all my retrofits and are well liked. We've lived with them for 7 years now. You do have to know you will hear traffic noise if on a busy street. Also, in high wind situations, I build a bit of a blister around them on the exterior for less blow back. I have lots of photos if needed.

    1. brian_wiley | | #14

      Hi Paul, do you find that the operation noise of them is noticeable? I’ve only seen videos of them in operation, but never heard one in person.

      1. pjpfeiff | | #15

        Yes it is noticeable, but I do run them on high because they're a bit undersized for the space. Let me describe the context: It's the attic of a Cape Cod where the floor area is roughly ~900 sq ft, but livable space is ~600 sq ft due to the sloped roofline. I have one Lunos in each gable end and my "office" is in one of two dormers. I put one of the pollen filters from 475 in the one farther from me and the stock filter in the one closer (for now). I feel like I can hear the one farther from me better, so I think the pollen filters make them slightly louder. In any case, even on high the sound basically falls into the background. If I have music on they're not noticeable. My wife and I slept in the space when we had guests and I actually found the sound soothing, although my wife did not. I think she probably would not have minded if they didn't switch direction, but then that's the whole point of them.

        On medium speed I think you would only notice it if you were listening for it. My computer, which is pretty quiet (but also closer to me), is louder. On low speed I can't hear them over my computer.

        1. brian_wiley | | #20

          Thanks for that info, Paul. My house would be on the cusp for a single pair, so I’d likely have to run them on high as well.

          I hadn’t considered the noise of them changing directions, and I’m nearly certain that’d be an annoyance for my wife. I, on the other hand, am capable of sleeping through a pancake compressor kicking on in the middle of the night.

  6. PAUL KUENN | | #17

    In highest mode, it is like someone blowing softly near the ear. Less than any fridge. Medium almost unnoticeable as Paul mentioned above. You cannot hear low. We have a small house and both are within 20' and my wife and I sleep soundly. The HPWH is louder but only turns on for 20 minutes a day during peak solar. On a side note, I have a separate 12v small pv solar system to run garden pumps and LEDs and have that run the Lunos. I through away the junk Chinese inverter it came with. At a meager 12w it certainly doesn't consume energy.

    1. brian_wiley | | #21

      That’s a great point of comparison with the HPWH. We had a AO Smith and I definitely could hear that at night when it kicked on, but it was at the other end of the house so it didn’t seem as present as something might in my bedroom. That said, it did fade into the background within a few months so maybe the Lunos would as well.

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