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Community and Q&A

Makeup Air for an Electric Dryer

KevinChan02169 | Posted in General Questions on

Hi Guys,
I just moved into my new construction house, and I’ve having issue with the dryer sucking out sewer gas from the trap when it is running. The house is extreme tight according to the HERS rater. It’s test at 0.74 ACH at 50 pa. The dryer is located at the finished mechanical room in the basement, which is also finished. Does anybody install a make up air for electric dryer? If so, what model? Thanks in advance.

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  1. Expert Member
    NICK KEENAN | | #1

    If you're sucking the water out of traps I would agree with your diagnosis that makeup air is needed.

    I'm trying to think of an elegant way and failing. You can put a current sensing relay on the dryer motor like this:

    Then install a motorized damper like this:
    You'd also need a 24v power supply. I'd try putting the relay and power supply in the dryer for a neat appearance.

  2. Expert Member
    Akos | | #2

    Say your place is 2000sqft. That means at 0.75ACH, you are looking at around 200CFM at 50PA. This is pretty close to the flow rate of a dryer.

    50PA is around 0.2" of wg, so there is no way it will suck air through a typical P trap which would normally have at least an 1" or 2" of water in it.

    My guess is your floor drain P trap doesn't have a primer and has run dry. I would re-fil the traps and see if the smell goes away.

    Sometimes also the lid for a sump tank is not well sealed. If you have one, I would check that as well.

    1. henryrose | | #3

      My house is currently not at all tight. I recently noticed a bad sewer smell in the basement. Two or three cups of water poured down the basement floor drain did the trick. Since water rarely enters that drain, it does dry out over time.

      1. Expert Member
        BILL WICHERS | | #4

        I make a point of pouring water down unused and lesser used traps every other month or so. Basement drains are especially important to check, but rarely used showers and bathtubs are another. I use a small watering can that I usually use for houseplants to pour water down those drains. It's quick and easy, you just need to remember to check every now and then :-)


      2. Expert Member
        MALCOLM TAYLOR | | #5

        For traps that don't get used, topping them up with mineral oil stops the water below from evaporating.

    2. KevinChan02169 | | #6

      Thanks. After checking, just found out the sewer pump lid wasn't close properly due to concrete went into the screw holes. I cleared that and see if the smell comes back tomorrow.

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