Since moving into our house we've had a nasty, hard to describe not quite sewage smell in and around our house.

It comes and goes. Seems to be related to cold and/or wet weather though we haven't really tracked that. Late last spring we flushed out the vents with a jet nozzle garden hose and put on a it worked beautifully for awhile. Now the smell is back. Do you think I need to have the vents jet cleaned professionally? We had a parade of plumbers out here. We had the sewer pipes camera inspected, nothing. We had the brand new septic re-inspected, nothing, etc. etc. Plumbers had all kinds of suggestions that we followed but none of them mentioned the vents - we KNOW that's what it is. Help!
  8 answers
  • KMS Woodworks KMS Woodworks on Feb 15, 2012
    When we have cool and damp weather we often get "down drafting" ...this is obvious as in this weather we are running the wood stove. We can see blasts of smoke that sometime descend to the deck then dissipate. These temperature "inversions" may be happening to you. You need to keep in mind that any vent stack is a direct air path to the septic system...and it will smell. having worked on many roofs you will notice this when up there. Why this is getting into your home is more of a you have a forced air HVAC system? and if so to you have combustion venting near any plumbing vents?

  • Donna McCrummen Donna McCrummen on Feb 15, 2012
    Yes, KMS we have forced air but the handler is on the other side of the house. Now that you mention that it could be down drafting in through the bathroom fans. That is where the smell is. How would I check that and fix it?

  • KMS Woodworks KMS Woodworks on Feb 16, 2012
    If the bath fans are running, they will pull air from inside the bath and vent it out through the roof or soffit type vents...If your fans are quiet enough you could run them during these cool periods. most homes "breath" to some degree and if the pressure in the home dips due to HVAC demand, open doors, drafting etc. Air may be pulled in these vents when not being used. Sometimes even the use of a range vent can cause a negative pressure situation in a home. Air will get sucked in by what ever means taking the path of least resistance... You could test this with some incense sticks at your bath vents... Test in a few configurations... Static with nothing running Range hood running HVAC running and then repeat with bath vents running ( this will be a bit like a DIY blower door test)

  • Donna McCrummen Donna McCrummen on Feb 16, 2012
    Thanks KMS - I've read so much on this subject but still don't understand the negative pressure thing. Will explain the testing further. I assume I'm watching the smoke from the incense stick right? What am I watching for? Air blowing in or out? What will it tell me?

  • KMS Woodworks KMS Woodworks on Feb 17, 2012
    The smoke will flow in the direction of the air flow...say a bath vent fan is running...the smoke should get sucked in and out of the room. when the vent is not running.... if the smoke flows back at you or down from the vent then air is coming in the vent instead of out.

  • Donna McCrummen Donna McCrummen on Feb 17, 2012
    I see - if the smoke is coming in I can assume I have a backdraft problem. Since the fans exhausts are very near the vent that could be my problem. I will have to move the exhausts or simply block the fans off.

  • KMS Woodworks KMS Woodworks on Feb 18, 2012
    adding a back draft type damper could help as well.

  • MarcioWilges MarcioWilges on Feb 02, 2015
    Yes, airflow is one of the things often overlooked by architects unschooled in the science of moving air around the house. While your bathroom vents are very efficient at the removal of obnoxious odors from the bathroom if there positioned incorrectly they can also function in the opposite manner, moving bad air from the outside in.