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Community and Q&A

ERV ducting

| Posted in Plans Review on

Can anyone tell me if the supply duct design is optimal for this ERV install? The wye seems to limit airflow to the 45 degrees elbow compared to splitting it 50-50 with Y. 

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  1. trojax | | #1

    Looks like the diagram doesn’t attach correctly.

  2. woodguyatl | | #2

    I am experienced with dust collection not ERV so take this FWIW. For the low volume of an ERV there likely no advantage either way. In general, the wye in the drawing is likely preferred since it adds less resistance to the longer ongoing flow which will naturally have more total resistance due to the longer pipe.

  3. Expert Member
    Akos | | #3

    What flow rate is the unit and what size and length are those duct runs?

    Generally you need some way of balancing airflow, this is much easier than with dampers near each register than with duct design. Duct design should aim to get it close, but you want to set it to design values when commissioning the system thus some means of adjustment are always needed.

    Since the rooms are not labeled, it is hard to guess where things are going but it looks like all the stale air pickups are in the bathrooms. Cooking is usually one of the largest sources of indoor air pollutants, so you want a largish (~65CFM) pickup there. I think this missing in your drawing. Once you add in the kitchen pickup, a typical ERV has enough capacity to clear one bath really well and two so-so, unless very large it won't do 4 baths+kitchen. Generally best is to put the ERV pickup in the most used bathroom and a standard exhaust fan in the rest. Simpler on the ducting as well. Don't forget a small pickup (10CFM) near the dryer, another source of indoor air pollution.

    1. exeric | | #4

      I agree about dampers. I would just use adjustable registers to even out the flow. Range hoods should always use their own dedicated exhaust fans because you don't want grease getting into the heat exchanger in an ERV. I think it can also be used as the primary reducer of cooked food odor. Install the ERV exhaust registers in the bathrooms with showers. No more than two showers for a 100 cfm ERV with two exhausts. Even that might be pushing it. Of course, use a boost switch in the bathrooms.

      1. Expert Member
        Akos | | #6

        Range hood is a range hood, it is a must in any house and should be ducted outside. The ERV pickup in the kitchen isn't for the range but for the general area. It should be kitty corner from the range, at least 8' away, well out of the way of any grease. No range hood has 100% capture efficiency, a lot escapes into the room/area, you want to have a way of exhausting this as soon as possible.

        In my own home, with an OK range hood, it takes about 2h to get pm2.5 levels down to baseline with the ERV. Nobody would keep the range hood running for that long to clear the air.

        Even something simple like making toast spikes pm2.5 levels. A range hood won't deal with that but an ERV would.

    2. charlie_sullivan | | #5

      That's the first I've heard a recommendation for exhaust near a dryer. A quick Google finds some articles with concern about fragrance in laundry products emitted outdoors from the dryer vent, but not particularly a issue indoors near the dryer. I guess a ventless heat pump dryer would put some of those fragrances into the indoor air. Some might be in the condensate, but I wouldn't count on that--better to use unscented laundry products in general but especially with a heat pump dryer. A gas dryer would also be a combustion gas concern if it didn't vent properly.

      Which of those is your concern?

      1. Expert Member
        Akos | | #7

        No dryer is air tight, even inside the dryer the connections leak. Besides VOC a lot of microfibers get exhausted, plus some lint always escapes the lint trap. I have a intake filter on my pickup next to the dryer and it needs a lot more cleaning than the other ones. That is with a taped and sealed exhaust connection, tighter than a typical home would have.

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