I am actually courteous about cleanliness, plus I make sure that our whole house is neat, organized, plus washed up. I clean up all surfaces down with good cleaner, plus our vacuum cleaner which uses a HEPA filter. I make sure to have the gas furnace professionally washed up every fall, plus the air conditioner gets tests on in the Spring. When I noticed a gross smell in the house, I had some trouble finding the source. I eventually saw that the smell worsened every time I started up the forced air cooling system. If the air conditioner ran all of the time, I ended up with a bad headache, and my daughter couldn’t quit sneezing, plus her child complained about a sore throat. However our Heating, Ventilation & A/C supplier had just recently checked, cleaned plus switched the air conditioner, I knew it was the reason for the smell plus our health complications. Washing the filter plus cleaning the supply vents did not help at all. I finally got back the Heating, Ventilation & A/C supplier to come in for another look at the cooling system. He informed me that there was most likely issues hidden in the duct system. Things, like the dust, pollen, insects, mold, plus dead rodents get inside the air duct, plus every single time the Heating, Ventilation & A/C plan operates, it spreads those smells, bacteria plus other air pollutants throughout the house. Also, the buildup of debris blocks the air, stopping comfort, placing more wear plus tear on heating plus cooling system.