There is no doubt that cleaning air ducts every seven years is as necessary as changing the furnace filter every 90 days. The air ducts are a very commonplace for dust, germs, mold spores, contaminants, and pollen where is constantly re-infects the air throughout the house.
Everyone that owns a boat, like me, knows that they are a maintenance chore. My boat is a 17' bass boat, but boat lovers love them in all sizes and types. The bigger the boat, the more work it takes to keep your prize in great condition. So, boat odors are a major concern. We find a little bit of everything that can sour your boating experience.
I was called in to test the indoor air quality for a young couple buying a home from the estate of an elderly man. Their concern was a potential mold problem as the wife was allergic to mold. The house was in very good condition. However, the wife felt dizziness and fatigued if she spent much time in the home.
Algae on the north and west side of a home is farily common. In any neighborhood, you will see several home that look negected and nasty because of algae that looks card or green on the siding.