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Community and Q&A

HVAC ductwork?

joenorm | Posted in General Questions on

I am considering installing a panasonic whispercomfort HRV(or is it an ERV?)

I was wondering about the proper duct and where to get it online?

Also, what are the preferred size and style registers?

Can they be located on the floor? or is in the wall or ceiling best?

Is the ducting small enough that I can drill through 2×10’s to run it?


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  1. joenorm | | #1

    Sorry, I meant Intellibalance.

  2. CramerSilkworth | | #2

    It's an ERV (does moisture recovery in addition to heat).

    It's connections can take both 4" and 6" duct. The 100 cfm it's rated for is a bit much in 4" (nearly 1,150 fpm, I try to keep these systems to 600 fpm) but would be ok for short runs I suppose. I'd use the 6" connections if you can (that's 510 fpm), for at least the main trunks (up until you split off with at least 25 cfm). But that all depends on how you're ducting it around.

    High in the wall or in the ceiling for the inlets & outlets is preferred. If you're including full baths in this setup, that's basically required to have any chance of getting the steam out effectively. But a floor outlet would be ok if it's not going to cause a nuisance draft.

    The ductwork itself can be off-the-shelf sheet metal from your local big box, just seal it well with tape or mastic. Or 6" flex if you can install it well (stretched tight, no kinks, etc). Or you can get fancy and use the Zehnder distribution system which is all 3" flex. It installs quickly, is air-tight and almost idiot-proof. ( There are other sources of similar products but you have to basically cobble together all the bits and pieces, eg:

    1. joenorm | | #3

      So if I have this unit installed in a 3bd/2bath, 1400 square foot home, can it take the place of both bath fans?

      I would just have an exhaust duct in each bath?


  3. CramerSilkworth | | #4

    Yes and yes. Locate the bathroom inlets/returns over the showers (or right in front of) and that should be plenty of exhaust. Could even do a third if you've got another space that needs exhaust air (basement? big storage closet?) Split the supply to the 3 bedrooms and maybe a 4th into the living room or whatever common space you've got.

  4. Expert Member
    Akos | | #5

    Not quite. The Intellibalance is not enough CFMs to clear two baths while still having a pickup in the kitchen area (you want this to remove cooking smells).

    It would do a decent job of clearing 1 bath though. I would plumb it up to the most used bath and install a standard bath fan in the other bath.

    1. CramerSilkworth | | #6

      If there's a vented range hood in the kitchen (a better way to handle cooking odors, IMHO), the 50 cfm each for the baths would be more than plenty. But if it's a recirculating range hood, yeah you'd want to pull 30-40 cfm from the kitchen as well. That'd still leave about 35 for each bath, which has been fine in many (many) bathrooms I've done with ERV systems.

      1. Expert Member
        Akos | | #7

        A vented range hood is a must. A recirc hood is only for air bnb type where you need a decorative range hood for the "look" and couldn't be bothered with punching a hole in the wall.

        Very few range hoods have good capture, a lot of fine particulate makes it past the range hood. You need some way to remove these, thus the pickup in the kitchen.

        When I'm cooking at home (vented range hood), I find that it takes about 2h for the IAQ to drop to baseline with my ERV on boost mode.

        35CFM might be enough to keep condensation at bay but not enough after taco night. Generally there is no such thing as too much bathroom exhaust, but there is too little. One area where over sizing is a good thing.

  5. joenorm | | #8

    Would there be a good reason not to use black corrugated drain pipe(without holes) as ductwork? Readily available and pretty cheap.

    1. Expert Member
      BILL WICHERS | | #9

      My guess is the “4 inch” sizes aren't the same between the two, so fittings would be an issue. That’s one issue with many piping systems: they all define their measurements differently so even if two systems are the same trade size, they often aren’t even close to fitting together.

      The other issue is that polyethylene is flammable. Most plastic systems used indoors have to meet certain standards regarding fire resistance such as the “vertical flame test”. Outdoor plastic systems don’t have this requirement.

      I would not use corrugated plastic drain pipe as air ducts within your home.


      1. joenorm | | #11

        Thanks. I read an article on here saying to use 4 inch PVC drain pipe as ducts so I figured polyethylene would be even easier.

        Points taken, will not use it.

        1. Expert Member
          BILL WICHERS | | #12

          PVC with the “DWV” mark is rated for “drains, waste, vents”. PVC is also self extinguishing and doesn’t burn the way polyethylene does. They are two very different materials.


    2. Expert Member
      Akos | | #10

      If you have no code, you can, otherwise you need proper ducting. Either way, I would not use drain pipe as the fresh air supply, it could be used for stale air pickups.

      Instead I would go with semi rigid aluminum ducting. HVAC supply places can get these in long lengths, you can do entire runs without any fittings. Way easier than rigid and only slightly more restrictive.

  6. joenorm | | #13

    Can I do all 4 inch ducting? The runs will not be very long if that makes a difference.

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