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Community and Q&A

Lunos e2 ductless HRV system vs. ducted system

Courtney McCracken | Posted in Mechanicals on

I am building a net zero house, 2000 SF, 2 stories. Can you tell me the pros and cons of the Lunos e2 ductless HRV system vs. a ducted system? The rep told me that 3 pairs of the Lunos e2 would be about right.

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  1. GBA Editor
    Martin Holladay | | #1

    Here's a link to a relevant article -- I don't know if you've read it yet, but if you haven't, it's a good place to start: Designing a Good Ventilation System.

  2. Brian P | | #2

    I'm not a building professional, but have looked into ventilation systems during various stages of our (now completed) very well air sealed net positive house. A few initial points:

    you should provide your location so those giving advice know your climate
    there are other aspects of your house that may affect ventilation systems...what is your heating plan? range hood type in kitchen? # of bathrooms/showers?
    you don't want to mess up this you'll need to do tons of research on your own until you fully understand ventilation systems and/or you may want to hire an independent consultant to help out

    A ventilation system need to accomplish two main goals: lower volume continuous ventilation for fresh air and higher volume as needed ventilation for showers/etc.

    The Lunos e2 can accomplish the first, but what about the latter? I'm assuming houses with a Lunos e2 system will also need bath fans (Panasonic WhisperGreen). In a really tight house, that could introduce make up air issues for the +/- 100CFM bath fan(s) you'll need. For material costs, you're now at least $3k+ for the Lunos and then +/- $500 for bath fans and parts. You're also now looking at 8 holes in your walls (6 for Lunos and assuming two bath fans).

    A well designed ducted HRV can handle both low volume continuous and as needed boost ventilation. High end (Zehnder) HRV systems can run well over $5k, but you can get other quality HRV systems for under that. Two holes in your walls, one supply and one exhaust for the HRV.

    Again, I'm not a building pro and the Lunos system looks cool...but from my perspective, it seems like a well designed and competently installed ducted HRV might make more sense.

    1. Valli Geiger | | #16

      I have an interest in well designed, highly efficient small houses. I ended up building a post and beam SIP panel 1050 sq ft house. Ducted HRV's are a huge expense and really awkward in a post and beam, cathedral ceiling house. We used two Panasonic Whisper Comfort ERV's, one for the main living space and one for the bedroom post and beam frame.

      The Lunos would have been a much better alternative if it had beed available when we were making these decisions. Easy installation, no need for ductwork and its inherent issues over time and brings HRV, dehumidifying as well. Wish we had known about it.


  3. Brendan Albano | | #3

    Lunos does have a product for bathrooms: although although other issues Brian brought up are still totally valid.

    It seems to me that the main pro of the Lunos is no ducts. Is this a big benefit for your design aesthetically or practically? Are you heating or cooling with a ducted system, or would the Lunos mean you had no ducts at all?

  4. Brian P | | #4

    The eGO does up to 27CFM in exhaust only mode. It will take an extended period to clear moisture out of a bathroom during showers...whether that is just a visual issue or an actual moisture issue, I don't know.

    For a full Lunos system in a 2000 sq ft house with two bathrooms:
    -cost is now at $4600 for just the units (3 pair e2 and two eGO)
    -eight 6" holes in the wall that need flashing and siding detailing
    -electrician time for power and connecting units

    Not trying to bash the Lunos system, just thinking through the full costs and issues versus a ducted HRV.

  5. Kevin Dickson, MSME | | #5

    Home Depot is selling something similar to the Lunos for $431:

  6. Courtney McCracken | | #6

    Thanks very much for the replies. Excellent points, especially that it is a very important decision and therefore should be made conservatively. And many more holes in the envelope. This probably won't change the answers but the house is in Mystic CT, has 2 full baths, heating and cooling by 2 mini splits (so no ducts except the HRV), range hood in kitchen (not sure if it will have makeup air capability). Just trying to save money. I guess I'll stick with the HRV/ERV.

  7. Kevin Camfield | | #7

    I am looking at Lunos also for a 2,200 ft2 home in the Pacific Northwest. I am planning a house using mini split heat pumps and no ductwork. I plan to shoot for Passive house levels of air tightness but not PH levels of insulation. It looks like Lunos has several options for ductless systems including passive vents and all-in-one type units. I am planning to have a rain screen on my house and I'm thinking the air inlets can be installed to draw air from within the rain screen so they do not have to penetrate the siding. This would be good from a water leakage standpoint and since we are on the water where the wind can get strong, I'm thinking it will be good also from a air pressure standpoint.

    Does anyone have any experience using these units?

  8. GBA Editor
    Martin Holladay | | #8

    You don't want to pull air from a rainscreen gap for a Lunos fan. For one thing, these fans reverse direction -- so you would be dumping humid indoor air into your rainscreen gap (during the exhaust phase), and the humidity would condense and freeze in the rainscreen gap during the winter. Bad idea.

    The Lunos fan is designed to penetrate through the siding to the exterior.

  9. Stephen Sheehy | | #9

    Courtney: A big consideration is the layout of the structure. Is there room for the many ducts needed for a traditional hrv? Our house has a large utility space running the entire length of the house, so installing hrv ducts was simple. Drilling lots of holes through framing might be problematic.

    We also have a mechanical/laundry room where we could locate the hrv unit and the inlet and outlet. Reducing the number of penetrations is certainly a consideration.

    A benefit to using Zehnder is that Zehnder will design your system and once it is installed, commission it. In early 2015, it cost about $6k installed.

    You can get MERV 13 filters for our hrv, which helps maintain indoor air quality. The filters are replaceable in a few seconds, which is also nice.

  10. Steve Vigoren | | #10

    Courtney, two story house would give you the opportunity to use floor trusses which give you room for ductwork between floors. You don't say whether 2,000 sq. ft. per floor or total. A utility/laundry room is a nice place for a HRV to live, as mentioned. I built a one story with nine foot ceilings in the front south facing half, and lowered the ceilings to eight feet in the back half, which gave me space for my HRV ductwork. My HRV lives in my cistern (water tank) room which is a room between my house and attached garage.

  11. Expert Member
    Dana Dorsett | | #11

    BTW: The TwinFresh Comfo units Kevin Dickenson referred to in response #5 are similar to the Lunos in some respects, but they don't seem to be operated in coordinated pairs to minimize pressurization/depressurization of the house. They seem to assume that the heat exchanger effect of all the air leaks in the house are about the same as the ceramic core in the ventilator unit?

    At any rate, the cost of a SINGLE TwinFresh Comfo at HD pricing is $431, or $862 for two, whereas Lunos are sold in pairs for $1055 at 475 High Performance Building Supply. The Lunos e2 cost $200 more, but is balanced ventilation, unlike the TwinFresh Comfo. The TwinFresh Comfo can operate up to 10 units in series (with only one connection to the AC power), but it does not appear to be designed to pressure balance the house like the Lunos.

  12. Kevin Camfield | | #12

    I doesn't really freeze where we are especially right up against the house, but it still is probably not a good idea to dump the hot, moist air up against the back of the siding. There is a lot of wind at our location. Will the air pressure difference overcome the fans in the Lunos?

  13. Expert Member
    Malcolm Taylor | | #13

    Check your building code. ours precludes ventilation intakes or exhausts from terminating in concealed spaces.

  14. Kevin Camfield | | #14

    Thanks. It sounds like it's generally a bad idea even for intake only. It would be hard to see if something bad were happening in the concealed rain screen space.

    Based on some very good feedback on this site and a couple of good articles by Martin, I'm leaning now towards just using the Panasonic fans in the bathrooms and a 100 cfm range hood. The architect currently has a total of 4 fans specified with a total airflow of 300 cfm. I will probably add a couple of the Lunos passive air vents. These are rated for up to 15 cfm each at 8pa. The balance of the air I assume will come from air leaks. I'm thinking of targeting for 1.0 ACH 50 and will look to use air sealed propane stove and fire place.

  15. Expert Member
    Malcolm Taylor | | #15

    I'm afraid I haven't been any help to your more central question, which was about how to terminate vents in a windy location. I don't know enough about the pressure differentials created by wind around a structure to know if one spot is better than another, or if baffles work. My only relevant experience has been with directional chimney caps - and they don't seem to. Maybe others can chime in.

  16. Jon R | | #17

    Old question but relevant to others: I'm pretty sure that under reasonable wind conditions, the Lunos fan pressure will be sufficient to maintain most of its air flow. Under extreme wind conditions, you will have so much flow through leaks that it doesn't matter what the Lunos does.

    There is some (how much??) advantage to locating erv/hrv vents low, away from corners and on other than the prevailing wind windward/leeward sides.

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