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HRV in basement to remove radon, and for air exchange/ humidity control on first floor.

JDG | Posted in General Questions on

Hi, looking at a potential HRV unit in basement to help with radon mitigation, as well as first floor air exchanging to help with stale air and humidity build up on windows. 

Plan is to have dedicated ducting. 1-2 supply and return’s on first floor (through the flooring). 1 supply and return in basement all to the same HRV located in the basement. 

House is 1920’s range, ~1060 sq/ft, 2 bed/ 2 bath, recently renovate, very air tight (new windows, spray foam ridge) located in North East. Currently running 95-pint whole house dehumidifier in basement that has been effective. Basement is old but clean, unfinished, for storage, work bench and laundry. 6ft ceiling. Field stone foundation. Concrete floor that’s half level, half over ledge. Floor has been epoxy sealed and rim joists sprayed. Sealed sump pump basin with buried perforated pipe running under concrete. Basement is dry and averages around 50-55% RH. The main floor averages around 50 RH, high/ low i have seen 45-65 RH. There is nothing in the floor joists, just felt paper/ hardwood floor, no barrier or insulation. Forced hot water heating. First few inches of widows get condensation at night/morning, but is gone by the afternoon. Colder climate, windows and doors are closed most of the year resulting in stale air, so air exchanging the first floor would be nice and likely recommended due to the spray foamed attic. Unfinished Attic is also conditioned space (for storage) for potential HRV and allow supply and return in ceilings of main floor, but would be near impossible to duct to basement. 

My concern is- is there any potential for contamination the first floor supply if I have a supply and return in the basement with known radon operating through the same system? Aware the supply and returns airs don’t actually mix passing though the heat exchanger. I’m assuming no, as long as i maintain equal pressures in basement and first floor. Thank you for any feedback. 

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  1. Expert Member
    Akos | | #1

    The only change I would make is to skip the fresh air feed to the basement, all you need there is a stale air pickup near the floor. This avoid the mixing issue you are worried about plus it draws in conditioned air from the house above into the basement.

    In colder climates an ERV tends to be the better option unless you have major wintertime high humidity issues.

  2. JDG | | #2

    Thank you for the reply. I did not think about putting the return vent close to the floor. I was assuming it would be near the basement ceiling. Any concern with a single only return in the basement potentially drawing more radon up? Would two returns on opposite sides of basement help mitigate more radon or be more of a concern with negative pressure?

    Still leaning towards HRV just for the winder months to help with humidity. For the living area, is there an advantage to having HRV ducting in the ceiling vs. the flooring?

    1. Expert Member
      Akos | | #3

      It will take an awfully good isolation between a basement and living space for any reasonable flowrate to depressurize the space, I can't see this happening. Without a pressure difference, it won't draw extra radon into the space. If the space is mostly open, I can't see needing more than a single return, a 2nd one won't hurt though.

      What is the source of your winter time humidity? Once construction moisture is out, you should not have high humidity with reasonable ventilation, an HRV tends to over dry the air in the wintertime. I'm running a mid range ERV (so not the best latent recovery) and once temperatures fall bellow 20F, the house humidity starts getting too low and have to run a humidifier.

      Fresh air supply tends to be cooler in winter time, so best to supply it either close by or into your hvac return, this way it can get tampered by the house heat. Otherwise somewhere up high and away from people is the best. I would avoid above any sitting area.

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