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ERV With Limited Ducts

Cldlhd | Posted in Green Products and Materials on

I have a pretty well sealed smaller single story house, I recently bought an Airthings wave plus and apparently my CO2 is higher than ideal ( regularly between 1,000 and 2,000) and even though it’s on a slab my radon is between 4 and 5. I have some cracks to seal where the foundation meets the slab but have thinking about installing an ERV ( leaning towards the Panasonic fcv-10vec2 but persuadable) and was wondering if it would be effective if I only had one intake and exhaust duct to the house. They would both be on the same end of the house sharing a wall but divided by a brick wall/ fireplace that bisects the room most of the way – it’s a combination kitchen/ living room that’s 22’x19’. There would be no ducts running to the 3 bedrooms at the back of the house but the doors are usually open. I thought maybe the air flow would “short circuit “ and was wondering if it would be worth it. I could run ducts but even insulated I figured being in an unconditioned attic ( probably about 25 degrees F right now and gets to 110 to 120 in the summer) it would kill some of the efficiency of the ERV’s temperature recovery. The ERV would be in a storage room attached to the house that shares the wall where I want to run the ducts through. This setup would be a lot easier but I’m willing to run ducts if needed. The hvac is a Mitsubishi mini split hyper heat for the previously mentioned room and hyper heat multi splits in the bedrooms ( all wall units ). Currently on the exhaust side I have a bathroom exhaust fan, a dryer vent and a range hood and no intake other than what leaks in .Any information is appreciated.

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    I'll give your post a bump.

    Non-expert here, but all the instructions I've seen include dedicated supply and return ducts. If you don't want to that, you might be better off with spot ventilation using a through wall system or something like a Panasonic FV-04 (which still requires some ducting).

    1. Cldlhd | | #2

      Thanks. I thought about that Panasonic model but I figure it only has one intake and exhaust point in the house and if I have to run ducts I might as use the Panasonic fcv-10vec2 and run ducts to multiple locations. I was planning on putting it in an attached semi conditioned storage room and running the ducts through the wall avoiding putting them in the unconditioned attic so I can avoid the efficiency hit. My storage room is around 50 f and right now the attic is around 30. Maybe I’ll upload a sketch.

  2. C L | | #3

    Not sure what you are trying to achieve.
    If you don't want to run any ducts except the intake and exhaust, consider the Panasonic whisper quiet series. About half the cost and only in and out. It draws from the room it is in, and dumps fresh air into the same room.

    HOWEVER, if you have even a relatively tight house, and your HVAC system is unducted minisplits, please consider some way to dump fresh air directly into the sleeping rooms. In that case, either use a ducted system (even if the ducts go through an unconditioned space - ERV ducts are small, and you can embed them in ALOT of insulation, so that they are not totally in an unconditioned space), or dump the ERV fresh air directly into the sleeping room.

    This is even if the way you currently use the space is to keep the sleeping room doors open. The space not always be used that way, and you increase fire safety if you keep the sleeping room doors closed. But you need fresh air.

  3. Expert Member
    Deleted | | #4

    Deleted

  4. Cldlhd | | #5

    Thanks. I guess it's hard to get across without posting a sketch of my house. But yes, I was thinking just one intake and exhaust and I know the whisper quiet is cheaper. The only downside for me was the running ducts in the unconditioned attic plus aesthetically it's a little more intrusive. With the intelliChoice 100 mounted in my semiconditioned storage room (it gets indirect heat from the house) the ducts would be in the semi conditioned well insulated storage room rather than the attic and would run through the wall. Maybe I'll run ducts in the attic and just try to insulate them real well, I just had a vision of them sitting in my 120° attic all day during the summer.... That way I could get fresh air into the bedrooms. Kind of wish I would have thought of this a couple of years ago before I remodeled those bedrooms.

    So should each room with an intake also have an equal size exhaust? I don't think I'm getting really good air exchange because according to my AirWave Plus, not sure the accuracy, our CO2 level is often up around 1500 PPM. Thanks

  5. C L | | #6

    "So should each room with an intake also have an equal size exhaust? I don't think I'm getting really good air exchange because according to my AirWave Plus, not sure the accuracy, our CO2 level is often up around 1500 PPM. Thanks"

    It depends upon how leaky your bedrooms are, how much undercut you have on the door, etc. If there is exhaust, that is more pressure on the supply and you might get less supply. You could install a transfer duct (through your attic, or if your crawl is conditioned, through there). Bedroom CO2 is my issue also...

    I still don't understand why, if you don't want to do internal duct distribution, you can't put a Whisper Quiet in your semiconditioned storage room, and run it's ducts the same way you were going to run them for the Intellichoice?
    However, I do think dumping the fresh air into the storage room is not the best idea - you need it in the bedrooms, which probably moves you to the Intellichoice.

    In your routing through the attic, can you put a return air type box up there the full width of the joist bay, and have a 4" duct come off the side, tight to the attic side of the gyp ceiling? That leaves you your insulation depth -4" of insulation over your duct if you can route the duct entirely in one joist bay. That is hardly unconditioned...

    1. Cldlhd | | #9

      Sorry I probably didn't explain that right. I was going to mount the intellichoice in the storage room and run the intake and exhaust ducts through the wall into the living space. I wasn't going to dump the air into the storage room. Basically the storage room was just going to be a place to mount the unit and run the two ducts to the outside and then run two ducts to the inside. I'll probably end up putting it out there and running ducts through the attic to the rooms. The bedrooms are pretty well sealed, I have zip system sheathing on the outside of them and closed cell spray foam inside the wall and new windows.

  6. Kyle R | | #7

    Have you considered the Lunos product?

    1. Cldlhd | | #10

      I looked into it a little bit but admittedly I’m just starting down this road. I like it but the only hassle I see is getting the wiring to it in some rooms. The 2 bedrooms have been remodeled and have closed cell spray foam , all new drywall etc. not impossible but not real eager to open the walls up.

  7. Trevor Lambert | | #8

    I wouldn't expect you to get good air quality throughout the house if you just have one supply and one exhaust. That's even if they're on opposite sides of the house. It can only be worse if they're in the same room.

    Yes, running ducts in an unconditioned space will hurt the efficiency of the recovery ventilator. But you can help that by insulating the ducts, and don't lose sight of the fact that ventilation is the primary function of the unit, the heat/energy recovery is secondary.

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