After reading everybody's comments in this blog, I feel so much relief, I thought I was the only person in the world who was dealing with this mysterious odor. After much research crawling under the house and looking at the centralized area below the room that had the foul odor, we have found out that insulation is an animal attractant especially in extreme climate, whether it be hot or cold. So most likely what all of us are suffering from is in fact animals. For the longest time we saw no evidence of any kind of Critters. And then we began to hear the sound of a rather large animal scratching, and squeaking or whimpering. What was discovered was the animal was between the insulation and the bottom of the house. It was not in our ductwork as we originally thought. But after harboring for such a long time and having babies or inviting other family members in it's cozy little Hideaway, the smell of feces and urine and ammonia begins to permeate your subfloor and seep into your house. Once the animal feces covers a large portion of your insulation it compounds the problem . Cellulose insulation is paper based, but it is also treated with chemicals (borates) that suppress mold growth. Fiberglass does not support mold growth, but it gets dirty, and the dirt grows mold, and it is often paper faced and this paper grows mold. So this being said, can the chemicals in our insulation mixed with pet urine create an even stronger ammonia smell and grow mold? The answer is yes!
So what is the solution? We are still dealing with this, we have found the culprit and now we have to come up with an answer. Our thoughts are to get industrial strength aerosol bombs and place under the house between the insulation and subfloor. We have the ability to do that, not all houses will. Homes that cannot, perhaps just put the bombs under the house. But just as the pest smells permeated the house, I can only imagine the smell of the bomb will too. Then health issues are always a concern with smelling either. However, we are willing to try this & hopefully run this creature out and then begin the deodorizing process. It will be necessary to run an air filter in the house for several days possibly even weeks until we feel the air in the house is once again pure.
Best of luck to everyone out there getting rid of their pest problem. We have been dealing with this for almost a year and it is getting worse as the feces continue to grow bigger from more pest coming in to join its family member. But we say good riddance to them all. I hope this helps.