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No HVAC Installers Install Dedicated Ductwork for ERV??

mrigney | Posted in General Questions on

Some of you might’ve seen my previous post about communication issues with my builder about an ERV w/dedicated ductwork. We’ve had some good conversations about it, and I think have worked it out. Thanks to those of you who replied. Onto a new question.

The HVAC contractor he normally uses has never done an ERV with dedicated ductwork (and doesn’t seem interested). He’s called a couple of other companies so far and they all have said they don’t do dedicated ductwork for an ERV. I’ve even gotten in the act and called a couple over the last day. Same answer from all of them, “you don’t need dedicated ductwork; all you’re trying to do is get oxygen into your house if it’s spray foamed.” Per Martin’s article about ERV/HRV ducting (and others at JLC, finehomebuilding, etc), it seems to me that dedicated ductwork is the way to go. Is it that unusual to do dedicated ductwork for an ERV? I’m at the very northern edge of Climate Zone 3; ERVs are definitely not common around here.

And I guess my follow-up question is…how big of a deal should I make the dedicated ductwork? My builder has said he’ll make it happen, but what’s the cost going to be to wrangle an hvac company to do something they’ve never done before? If it matters, my HVAC unit is a Carrier Greenspeed Infinity (https://www.carrier.com/residential/en/us/products/heat-pumps/25vna0/ and https://www.carrier.com/residential/en/us/products/fan-coils/fe4a/).

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Matt,
    Installers of Zehnder equipment insist on dedicated ventilation ductwork. The key is to find a contractor who specializes in ventilation. We've had those kinds of contractors in Vermont for decades, but they may be rare elsewhere.

  2. charlie_sullivan | | #2

    If you go with the Zehnder system, they design everything and send you a box with all the parts that snap together. It doesn't really take any special HVAC skills so do it. A smart carpenter who's willing to take the time to figure it out can do it, and likely do it better than a HVAC contractor who thinks he already knows everything. The challenge is that you'll pay for the time it takes the carpenter to figure it out, as well as paying the premium price for the Zehnder system.

    1. mrigney | | #3

      I'll check into this. Heck...I'm fine doing the work myself if need be. Not sure how the bank would feel about that. Ha.

    2. mrigney | | #4

      Quick follow up...how much of a premium are we talking for a Zehnder roughly? House is 2100 sq ft.

      1. BurkeW | | #9

        You can fill out a form on their site and provide your project details and they will design it and send you the cost.

        I did this just to see how much it would be for our house, and it was very expensive. Somewhere in the range of 3-4x what we are paying for a non-zehnder installed with dedicated ducts.

        That said, if I could have found the room in the budget, I would have loved to get a Zehnder!

  3. Expert Member
    AKOS TOTH | | #5

    Since you have a modulating unit with an ECM blower, I would just duct to the air handler. It is a bit too late to add in the ducting and well set up with the right equipment, the ducted unit should work reasonably well.

    Important item to interlock the furnace blower with the ERV but set the blower on the furnace to run at its lowest setting (200CFM is plenty if you have a 100CFM ERV). Most ECM blowers at low flow rate consume 20W to 30W, so it is a bit more than the ducted setup but not a huge energy cost.

    Make sure to get an autobalance ERV and make sure the pressure drop in the return duct is well within the balancing range of the unit. You want to make sure that no matter what speed your air handler is running at, it doesn't cause the ERV to get out of balance.

    Provided the system is set up right and commissioned properly, you'll get a decent system that will be much easier to install.

    1. mrigney | | #6

      Thanks for the informative reply, Akos. This is helpful in evaluating the decision. Like my other post related, I had anticipated dedicated ducting for the ERV, but with drywall in now, it obviously becomes much harder. The builder has said they'll cover any drywall work/retrofitting costs, but I'm just wrestling through what the best path forward is.

      My biggest concern (probably) with a system tied into the air handler was the balancing issues when the air handler is running at different speeds. Secondly was getting fresh air/stale air where I want it to go/exhaust from. Third was the energy savings issue. I knew it wouldn't be a massive cost difference since my unit has an ECM blower.

      Do you have a recommendation on an autobalance ERV? Something like Broan AI series? I assume by autobalancing you mean that the ERV "intelligently" adjusts flow rate of fresh/exhaust air based on changes in pressure due to the air handler running at different speeds? One of my concerns as I've learned that folks around here don't do ERVs very often is making sure I do get the good install you're talking about.

      I had thrown out to "hybrid" solutions to my builder. One a literal hybrid install (dedicated exhaust, supply air to the return plenum). Another was a single(ish) point supply/return where we exhaust from one or two strategic places and supply to one or two strategic places, then late the HVAC distribute the house over time. As you can see in the attached drawings, all bathrooms and laundry room are pretty easily accessible from the attic; as are all bedrooms. The great room/kitchen are basically the two rooms that would cause major issues for running ducts.

      Again, thanks for the feedback. I'm trying to be creative and work out the best solution. The guidance/literature I get here is way more extensive than what I can find locally.

      1. Expert Member
        AKOS TOTH | | #7

        How tall are your joists? Looking at the layout, you might be easy to fish a couple ducts from the attic space into the living room and kitchen. With the bedrooms mostly accessible, the fully ducted setup might not be that hard to install. If you have build pictures showing what is between the floor joists, should be easy to select a simple run.

        The only section of ventilation ducting that needs to be insulated is the one connecting the ERV to outdoors. Any interior runs inside conditioned space can be done with non-insulated ducts. These are much smaller and easier to work with. I've had good luck with retrofit installs with semi rigid aluminum ducting (think dryer duct but longer). You can get it in long length and run pretty convoluted paths. It doesn't have the restriction issues standard flex duct does.

        Your living room would only need a 3" flex fresh air feed and you want a 5" (or two 4") stale air pickup from your kitchen area. Make sure this is at least 8' from your stove. All your bedrooms can be fed by 2.5" or 3" feeds.

        You can also use the ducting made for high velocity AC units. The ducting is not cheap but pretty easy to use.

        1. mrigney | | #8

          Oh, good question on the truss height. I don't remember off the top of my head. They were big enough to run HVAC ductwork through, so plenty tall. I have a video of what's running up there in the trusses. Didn't take any stills (got stills of the walls). I thought it might be doable with the accessibility of most rooms from the attic space. Would really only mean fishing three ducts through areas that are currently inaccessible. I suppose even those, you could run by cutting a section of the 2nd floor subfloor up, running the duct in the joists from there, then just cutting drywall where you want the feed/pickup.

          Thanks for all the ideas. Honestly at this point, my big concern is finding an installer that I trust to do the job...I think I've done more research on ERVs than most who live in my area.

          Did you have a recommendation on an autobalancing ERV (brand? model?) if I do end up ducting directly into the HVAC?

          1. Expert Member
            AKOS TOTH | | #11

            I've had good luck with the Panasonic Intellibalance. It is a high efficiency, low cost, no frills unit that just works. At 100CFM it might be too small for your place though.

            vanEE (they make the Broan units as well) AI series look nice but I haven't used that series yet. Their regular ECM units work well, are pretty easy to install and setup.

  4. BurkeW | | #10

    We went through some similar struggles in our area, where efficient building and dedicated ventilation are not the norm.

    I ended up finding a local energy consulting firm that was familiar with what I wanted. Turned out that they also had a HVAC company within the group that knows how to install a dedicated system. Beyond that, they recommended a small number of other HVAC contractors that they had confidence in.

    Maybe you can find something similar in your area? You can expand your search statewide, and even into neighboring states. The folks I worked with were very familiar with our state and a few around it.

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