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New construction Zone 4C. ERV? HRV? Or just bath fans?

joenorm | Posted in General Questions on

I am framing a 1400 sqarefoot house at the moment and am wondering about an HRV, ERV, or just using an exhaust fan in each Bath?

The Lunos products look pretty cool, but as other have noted pretty expensive.

The layout of the house is two beds, bath, kitchen, and living on the main floor, and the mater bed with another bath as the second story. House is a rectangular box with shed roofs.

Now is the time to decide on this, as I can run whatever mechanicals necessary.

I’m wondering if there is a “go-to” solution for a house this size? Or are bath exhaust only fans acceptable?


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  1. Expert Member
    RICHARD EVANS | | #1


    I think the problem with Exhaust-Only is that you are then relying on the holes and gaps of the house as your source for supply air. It's hard to predict where these gaps are and this can lead to comfort issues and potentially moisture issues.

    As an example, suppose the exterior walls/ceiling of your master bedroom are really air tight. Very little supply air will make its way into your bedroom. This might lead to elevated CO2 levels at night. Perhaps the supply air will find its way through a gaps in your foundation which could lead to infiltration of moist, dank air into the home. You can control this by adding small intake holes in your bedroom, etc. These are probably less risky in your climate than a colder climate but still an imperfect solution.

    I think balanced ventilation is the way to go. It also requires less wall penetrations than a bunch of bath/kitchen fans.

  2. Expert Member
    Akos | | #2

    Exhaust only doesn't tend to work well for the reason Rick pointed out. It would also mean your furnace fan needs to run continuously to mix the air and ensure proper air changes in closed rooms. If you set it up carefully, it can work but even then not well.

    A better exhaust only setup is system example 3b from:

    With that setup, you are already running ducts, so the cost adder for a full ERV/HRV is not that much.

    For smaller house, you can't beat the cost and performance of the Panasonic Intellibalance unit. With an ERV, if you find your house is too humid in the winter time, you might have to run it on boost for the colder months.

    1. joenorm | | #4

      Where would be the best place to locate the supply and exhaust ports in a 3 bed, 2 bath, 1400sqft home?

      1. Expert Member
        RICHARD EVANS | | #5


        I have the Intellibalance unit that Akos described. So far it's been great. Panasonic makes a special port that serves as both an exhaust and a supply apparatus:

        This requires that only one hole be made. I would reccomend putting it on the gable side of the house and close to where you intend to out the unit. I would avoid having it too close to the ground.

        In a perfect world, you have two separate ports- one for supply and one for exhaust. These would be separated by at least 10 feet. I'm not sure how effective the combined supply/exhaust unit truly is. I hope to test our indoor air quality levels at some point...

      2. Expert Member
        Akos | | #6

        I would check your codes. Our requires supplies in all bedrooms, living space and basement. You need returns in the laundry, bathrooms and kitchen. Kitchen one is important as cooking releases a lot of VOC and fine particulates, a range hood captures most but not all of it.

        The return flow left over for bathrooms is usually only enough to properly clear one bathroom. The better setup is to hook up the ERV to one bath with a boost switch and install and exhaust fan in the other one.

        1. joenorm | | #7

          So with the Intelliballace do you simply make as many "splits" in the supply line as needed to get to all the bedrooms and living?

          Could this unit be placed in a Crawl Space?

          1. Expert Member
            Akos | | #8

            Pretty much. A main trunk (5" rigid or 6" if flex) and branches for each room. Our code requires 10CFM/room and 25cfm for the master, so if you have simple runs, you can do it with 3" pipe which would fit into a 2x4 wall.

            The return side pretty much the same, I would upsize the return from the kitchen (5") and bath (4") as most of the flow should be from there.

            If you crawl is conditioned, no problem going in there. Keep in mind that you need to change filters on the units, so should be somewhere accessible.

            These units are also pretty slim, you can probably mount it in the ceiling of a central closet, laundry room or hallway and run your ducting from there. Might be simpler runs.

  3. exeric | | #3

    Hi Joe,
    I concur with both replies. If you are in the construction stage it only makes sense to build as tight as can be reasonably done and then compensate for it. That means an ERV or HRV. You won't be sorry.

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