Replies

1. Expert Member
   NICK KEENAN | Dec 05, 2021 10:27pm | #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:
   https://www.supplyhouse.com/Aprilaire-50-APR-Current-Sensing-Relay-24V

   Then install a motorized damper like this:
   https://www.supplyhouse.com/Fantech-ADC4-4-Normally-Closed-Shut-off-Damper-with-Motor-24V
   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 | Dec 05, 2021 11:53pm | #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 | Dec 06, 2021 06:57am | #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 | Dec 06, 2021 10:10am | #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 :-)

   Bill

2. Expert Member
   MALCOLM TAYLOR | Dec 06, 2021 12:41pm | #5

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

2. 
   KevinChan02169 | Dec 06, 2021 11:10pm | #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.