Q: We are builders in the Philadelphia area. Over the past few years, we’ve experienced several cases of what we’ve been told is "carpet filtration" — dark ghost lines that appear on the carpet under doors and around the perimeter of rooms. We tested the hvac system and found a sizeable imbalance between the supply and return sides, so we added an additional central return system to equalize the pressures. Is the imbalance the major cause of the filtration? If not, what are the causes? We have had to replace some carpet, and hope that we don’t continue to be liable for a recurring problem.
