Renter blames allergies on the season, then checks a vent and finds 'move out immediately' mold

A renter said their worsening allergies seemed seasonal at first, after noticing heavy buildup around a floor vent and posting photos to the r/hvacadvice subreddit. They wrote that the filter looked normal, prompting them not to inspect the vent earlier, but commenters urged urgent testing and faster action from the landlord. Users warned the material could be “move out immediately” mold and described the growth as significant for a floor register. The article notes that a clean HVAC filter doesn’t guarantee the rest of the system is problem-free, since filters mainly protect equipment. It also says renters should document issues, notify landlords in writing, and request professional inspection, while homeowners may reduce energy waste with efficient HVAC upgrades.