Were previous owners smokers? We redid a rental house & got new screens, 2 coats paint on each room, completely redid the kitchen, new cabinets, countertops, new appliances, light fixtures, etc. New floors & new carpet throughout. As we worked of course it was fall & had windows open. Right after realtor started showing the house to renters it got cold & we had to turn on heat, wow, did the house stink, we opened up that furnace door & it was dark dingy yellowed smoke, stale stink. so hours more of bleach water & cleaners before the place was pretty good. We added bowls of vinegar at night & hid them in the morning. by the time renters moved in it was pretty good. So try vinegar bowls where kids & critters can't get at them Open box of soda in closed in areas might help. Take a vent cover off & wipe out area of vent & rinse rag out in clean bowl of water, is it all brownish? Then it's probably the vents, if it is just dirty water with no smell that might not be it. I took a long skinny broom to couple of my vents a few times, got almost nothing out but I had gotten a high quality duck tape for attics & seams & so I guess nothing get in them to speak of. I have allergies big time, also clean out the area under furnace where air goes into to it from hall. I put a heavy piece of carpet pad that is covered with plastic on the floor under there & then wipe out couple of times a year by taking vent cover off. Of course no 1 smokes in my house but that area does get some dust. Yes fridge, freezers & humidifiers have drip pans that need cleaning or they can make you sick. Also if you have any drains that don't have water in the elbow sewer gas can come up & make you very sick, is there drain in center of basement floor- be sure to put gallon of water down it often or keep it covered, upstairs bathroom not used, get water in all the drains including tub or shower. Good Luck, Hope you find the problem soon.

When you catch a whiff, I'd take the trap apart and see if there is any water in it. I suspect the trap is dry and you are smelling sewer gas. Realistically, unless your directional sense of smell isn't very good, it really can't be anything else. If the trap is dry, your vent is probably plugged and another fixture is siphoning the trap. IMHO

Thank you David! When having this house renovated post purchase, much of the bathroom was gutted and the sink I had installed is one I bought new some years before and was waiting to use (American Standard Standard Collection Console sink with oval glass shelf.) Because the works underneath are totally exposed I bought the best chrome P-trap and fittings a local plumbing supply house had. In a month or so I'll have my plumber back to install a pump for my utility sink, and he will need to add another vent stack I believe, so I'll have him see if the sink is connected to the bath vent, and if the vent has any blockage. I'll ask him about the air admittance valve - thank you so much for that information!

Hi, Yes. Poke holes in a few bags of charcoal or place charcoal pieces into a nylon or breathable bag and place it in the area that was painted. The charcoal has absorbent properties that will trap smells within the microscopic air pockets within. You could also buy boxes of baking soda and place the boxes in the area. It has the same effect. If you found this helpful visit http://doveshomeservices.com