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Community and Q&A

ERV Return in Laundry / Mech Room

megapointe | Posted in General Questions on

I am in the process of an energy retrofit of my 1940s house in CZ5A where I’ve replaced my gas forced air heating system with a ductless heat pump. I’ll soon have my exterior walls injected with foam, attic insulation vacuumed, and the underside of my roof foamed with open cell foam. Because I’ll have a much more air tight house and my air conditioning system is ductless I plan to install an ERV soon. Finally, as part of some plumbing updates I’ve replaced my electric water heater with a heat pump water heater.

I’ve been pleased with the heat pump water heater so far but I have noticed the fan does cool off the basement quite a bit. My water heater is in my basement in a combined laundry / utility room. My plan is to put a return for the ERV in this room as it is standard to have returns located in laundry rooms. I’m hopeful that the return on the ERV will actually help to exhaust some of the cool air put off by the heat pump water heater. 

Is this logic flawed or do you think I’ll actually have luck exhausting this cool air from the water heater and laundry room before it conditions the air in the rest of the basement? I understand I can duct the cool air from the water heater to the outside but I’m hoping the ERV setup will actually help me avoid another envelope penetration. 

Thanks for any insight and comments.

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  1. mr_reference_Hugh | | #1

    Your comment

    I’m hopeful that the return on the ERV will actually help to exhaust some of the cool air put off by the heat pump water heater.

    My comment:
    I think of it this way.

    What if the only return was from the coldest spot in the house?
    The HRV would extract say 60% of the heat from that "cold" air.
    There is not much heat to recapture in that cold air.
    The HRV would supply colder air to each supply vent than it would if the air was being pulled from the "occupied space".
    The HRV would be exhausting the cold air; however, the HRV would struggle to effectively heat the incoming air that is going into the supply ducts.
    The supply air into the rest of the house would be cooler.

    The supply air into the rest of the house will be slightly cooler if you have a % of the return air coming from a cold spot.

    Your hot water tank is already using the heat in the air in your utility room to heat your hot water. By putting a return vent in the utility room, you are not increasing the heating load of your house at all, or so little that you will not notice.

    Also consider that if you ONLY have the ASHP from the hot water tank going outside and you have a really tight home, you might need to have a make-up air system??? Question marks here are because I don't know the volume of air your hot water tank ASHP is processing in a given period of time. I don't know how tight your home is.

    If you expell the hot water ASHP air outdoors, you need to consider any gas appliances you might have.Do you have any gas appliances that could backdraft and have really really serious problems for you and your family???

    1. megapointe | | #2

      Ahh yes that makes total sense and I don't know why I didn't think about it. The cold air from the utility room is going to go through that enthalpy core and effectively condition the incoming fresh air which will be slightly cooler than desired as a result. Makes sense.

      No gas appliances in the house! Part of my energy retrofit has been removing all gas appliances. Thanks for your help!

  2. Expert Member
    PETER G ENGLE PE | | #3

    You mentioned future insulation using open cell spray foam in the roof. Open cell foam is not appropriate for your climate, as it is air and vapor permeable. There are lots of reports of roof failures with open cell foam due to moisture finding its way to the cold sheathing in winter. If you are going to spray foam the roof, closed cell is the correct option for CZ5. You could also do a 50-50 split of R-value using CCSPF against the sheathing, and your choice of fluffy insulation inside of that.

  3. aunsafe2015 | | #4

    Mind sharing which heat pump water heater you bought? And whether you have any noise complaints about it?

    1. megapointe | | #5

      We purchased the Richmond model through Menards. It definitely makes some noise but I guess it doesn't annoy me as much as it does some. We have it in a laundry / utility room in the basement that will eventually have insulated walls around it so we know it will only get less noisy. The noise it makes reminds me of the noise you'd expect from an old fridge or freezer.

      1. mr_reference_Hugh | | #6

        I’m curious because I read so many posts about noise.

        Is there a reason you would not build full height walls around the unit and sound insulate the walls and the floor above.?

        Instead of venting the unit to the outside (which always remains an option for later) , just vent the heat pump into the laundry room.

        The walls would not be too expensive to build because of how small. Also curious because I was thinking of getting one myself.

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