I have a one year old home which this past summer, I was getting a sewage smell. At first is was only happening on a windy day. I'm on septic system, my floor drains in basement are always full with water. I was getting the smell in my sons room through the return air grill.. After I figured that out, I blocked it and the smell moved to the hallway return air grill. A couple of time in the summer after somebody uses the washroom, the smell got so bad that we had to leave the house for a bit. Now that the summer is gone and winter is here, I do not smell it anymore. I do know that when I go on the roof, you can smell the sewage smell really bad. Somebody told me to put a 90 degree pipe on stack to prevent the wind causing downdraft. That helped a bit, but the smell was still there. I had everyone look at this, even the plumbers. Everyone is stumped on this one. The plumber thought the smell was coming in through the HRV (which doesn't run in summer). We blocked that off, but the smell was still there. Sewage tank is completely sealed with caulking. The other thing we noticed is that it also happens when my wife does laundry. Let me know what you think. This is really bothering me because I've been working and trying to figure this problem out.
