We are experiencing an odor in our laundry rooom area. It seems like the odor only appears when the weather gets colder. We experienced it last year also around the same time but were hoping it would not come back. Unfortunately it did and we are stumped as to where the odor is coming from. It also seems like the odor is more apparent with the agitation of our water. We have septic and we have checked where the septic comes in to the house and there is no odor coming from there. We have a bathroom connecting to the laundry room also with its own heat source (electric). The odor also is noticeable around the area where our thermostat is located on the bathroom wall and through our dryer... weird I know. We are at a loss so if anyone can provide any ideas or information it would be appreciated

Is there a drain vent line that is disconnected somewhere in a wall or in the basement? Is there an unused trap somewhere that is dry and letting sewer gas back through it into the house? Floor drains are bad for this.