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Community and Q&A

Reducing wintertime ventilation

Steve Knapp CZ 3A Georgia | Posted in Mechanicals on

I have an Ultra Aire ventilator and dehumidifier (80 cfm) and a Panasonic ERV (20 cfm) that deliver outdoor air into my 3,200 square foot home. The Ultra Aire is installed in the basement and dumps air into a space near the central air handler. The Panasonic is on the second floor.

During the cooling season, I can easily maintain indoor humidity between 40% and 50%. During the winter, levels typically are in the mid 20% to 30% range.

If I shut off the Panasonic ERV for the winter, my ventilation rate will be about 80 cfm. Would this be adequate for two occupants? I suspect Joseph Lstiburek would say yes (or that I should reduce ventilation even more). Not sure what Max Sherman would think.

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  1. GBA Editor
    Martin Holladay | | #1

    According to the ASHRAE 62.2 formula (7.5 cfm per occupant plus 3 cfm for every 100 square feet of occupiable floor area), you need 15 cfm + (32 x 3 cfm) = 111 cfm.

    It's your house, though. You can ventilate your house at any rate you want -- whatever works for you.

    For more information, see these two articles:

    Designing a Good Ventilation System

    How Much Fresh Air Does Your Home Need?

  2. D Dorsett | | #2

    Is the occupancy 24/7 in winter or are you only home certain hours of the day?

    Dropping the ventilation rate to zero when you're away isn't usually a problem. And while you're away you're not showering cooking breathing or doing other activities that add moisture to the air, which makes the unnecessary ventilation more drying than when occupied.

  3. Alan B | | #3

    @ Dana
    Man, talk about a vacation, i can't wait to do without food, oxygen and showers on my next time off :P
    Sounds incredibly relaxing :D

    I know you meant this is just not happening in the home, but tbh i would maintain some ventilation though drop the rate greatly, VOCs and odours linger from furniture, carpets, pet dander and so forth, houses can be stuffy when you come back, i've had it happen.

  4. Steve Knapp CZ 3A Georgia | | #4

    Thanks, Martin. I will do further reading.

    Dana. We are here 24/7 except for occasional outings.

  5. GBA Editor
    Martin Holladay | | #5

    Your answer provides evidence supporting the wisdom of my advice: every family needs to determine their own favorite ventilation rate.

    If you are the type of person who is concerned that your furniture and cleaning supplies are off-gassing, it makes sense to ventilate your home for 24 hours every day.

    If you are the type of person who is worried about energy use, and who is pretty sure that your furniture isn't off-gassing much, and who is pretty sure that your cleaning products are relatively safe, you probably want to turn off your ventilation system when no one is home.

    Every family is different.

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