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Community and Q&A

Creating Conditioned Space for HRV

armindilo | Posted in Mechanicals on

When I bought my house 3 yrs ago the existing air exchanger was in the attic. It was not functional, and the ductwork was a mess. I removed the ductwork and stuffed the remaining holes with plastic bags and insulation (temporary measure!), planning to install an HRV properly in the future.

Well, the future is now approaching and I’m looking at my options. I’ve looked through just about every applicable HRV/ERV/HVAC on here, so I am well aware that the HRV can’t go in unconditioned space, and ideally the ducts wouldn’t be either.

The problem is, there is nowhere else to reasonably put it. The little bit of basement I have would require putting the outside intake/exhaust right beside the neighbors driveway or in an area that gets covered in snow.

So having said that, what can I do? I’m thinking maybe build a small “room” in the attic, properly air sealed and insulated from the rest of the attic. And then run the ducts in the attic, buried under blow in cellulose.


Central Newfoundland, zone 6/7.
Electric heat, no existing ductwork.
2 storeys + finished basement.
The basement has a small utility/laundry room, the rest of the basement is a separate apartment.

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  1. Expert Member
    Michael Maines | | #1

    Your situation is one where Lunos units make sense: They aren't inexpensive but they solve the problems you are facing and are very efficient. If you compare their cost to building a conditioned chase in your attic, you might find that the Lunos is the better value. But they aren't perfect; you can hear the fan change directions every 70 seconds, though it's quiet; they let in sounds from outdoors, and most homes would need more than one pair to have adequate airflow. If those are problems for you, then go with the conditioned chase in your attic.

    1. armindilo | | #2

      That's an interesting option. Wiring them would be a major hurdle in this house; there would be a lot of drywall and vapour barrier repair. And for adequate airflow I would probably need 3 pairs. (4 bedrooms, 3 bathrooms, and a laundry room on 3 different levels of the house).

      Thanks for the link. I don't think I'll go this route, but I'll keep in my back pocket in case the HRV is not feasible.

      1. this_page_left_blank | | #4

        You'd need more like 8 or 10 pairs. $15,000 better spent on something else. Actually could be $21,500, depending on options.

        1. Expert Member
          Michael Maines | | #5

          A typical 2000sf, 3-bedroom house needs about 60 cfm: Three pair of Lunos E2 provide that amount of air flow. The product cost for three pair is $3360. Compare that to buying and installing a central system with ductwork, which will be in the $5K to $10K range, or higher.

          1. this_page_left_blank | | #7

            He's in Canada, so I got the prices direct from Lunos Canada. $1500 for the most basic options, which doesn't even include smart control, up to $2150 per pair. 60cfm wouldn't meet minimum code for a two bedroom house here in Ontario, not sure about Newfoundland. Code aside, best practice we should be aiming for 600ppm CO2, maybe 800 at worst. The latest studies show that 1000 is too high. Based on that target, 60cfm is good for 2 adults and maybe a small pet, regardless of number of bedrooms.

          2. Expert Member
            Michael Maines | | #8

            Reply to #4: as far as I can tell, both Ontario and Newfoundland use ASHRAE 62.2-2016 for homes. For a 2-br, 2000sf home, that would be 83 cfm, which can be provided by four pair of Lunos E2 or three pair of Lunos E2-60. Still comparable or less in cost than a central, ducted system, especially if a newly insulated space needs to be created.

            If you don't want to use Lunos, then don't use them. I rarely do myself. But they are problem-solvers for specific situations, including this one. In any case, nowhere near 8-10 pair would be required unless you need to ventilate every room, which of course is best practice but not always necessary.

    2. richard_r | | #3

      The new model e2-60 is supposed to be quieter and has overlapping fan blades to reduce the outside noise.

      1. Expert Member
        Michael Maines | | #6

        I hadn't seen those, nice. Two of them would meet IRC airflow requirements for a typical home, though you may want more so each space is ventilated.

  2. Expert Member
    Akos | | #9

    Zone 6/7 and electric heat.

    I think what you should think about is ducting in cold climate heat pump. That will easily cut your heating bill by about 2.5x.

    Once you have the ducted heat pump, it is easy to connect to it an HRV/ERV and use the heating ducts for air distribution. This will take up space, no way around it. Some slim ducted units can be installed in vertical orientation (ie Fujitsu, Carrier/Midea) which can fit in the back of a closet. With some careful layout the HRV/ERV can be installed bellow the unit and plumbed into the return.

    An ERV tends to be the better option in cold climate as it doesn't need a drain and will spend much less time in defrost than an HRV. It also removes less moisture in the winter which is a good thing for a house that is not super air sealed.

    1. armindilo | | #10

      My future plan (2-3yrs) is to install 2 ductless mini-splits. I would do it now, but it will require changing my electrical panel, or adding a sub-panel (which has it's own set of problems due to space limitations). It will also require some work through the basement apartment, and I want to wait until there is no tenant there so that I can do a full reno on the basement, including upgrading all the copper to PEX for the whole house. It will also require some landscaping changes in the yard because of where I would need to to put the outside units. In a perfect world, I would do it all at once, but time and money....

      I am undecided about HRV vs ERV. As it is now, with 5 people in the house, we don't have an issue with dry air in the winter, and sometimes we are even running a portable dehumidifier; However we also aren't getting a lot air changes. From a quick look at an online calculator, brining in -10°C/75%RH air (typical winter day here) and heating it to 22°C brings it to 14%RH, which might be a bit too dry. Maybe an ERV is best. Not having a drain might matter, but where I am thinking of putting the unit in the attic I am pretty confident I can drain the HRV to the tailpiece of the bathroom vanity directly below.

      The major issue with any options I've looked at is the layout of the house and the lack of space. I really don't want vertical chases intruding into the rooms that they would need to go through because those rooms are already limited on space. I'm not against opening walls and putting rectangular ducts through them, but most of the walls that would make sense for that are load bearing, so I can't just cut a chunk out of them. And I'm also not really willing to give up the storage space in the bedrooms; the bedroom closets are already smaller than I'd like them to be (mostly 4' wide). If I didn't also have to run ducts, I would consider taking up closet space for an HRV, but between losing the closet space and the massive intrusion for ducts, it just doesn't seem worth it.

      I could possibly mount an ERV on the highest point on the wall above my open stairs. It would be a bit of an eyesore, especially since it would cast a large shadow from the window, but it would be possible. I would still end up having to run the ductwork up through the attic though, but that would be better than having the ERV and ductwork both in the attic. I hadn't really considered that option before because I was factoring in the drain for an HRV, which wouldn't be possible in that location. But now looking at just an ERV, it could work.

      And, actually, thinking about the ERV/drain thing some more, I may be able to bump it up into the attic area without building a separate "room" up there. I may be able to put one between the ceiling joists/bottom chord of the joists, again running ducts through the attic. (framing, vapour barrier, insulation, drywall as required to maintain proper barriers.)

      Thank you for your post. It has tweaked my brain to think of some options I hadn't considered.

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