Performed preventative maintenance on Lennox gas furnace. Changed the #201 filter. Serviced the power humidifier and replaced the #35 water panel. Tested the humidifier for proper drainage and to verify no leaks. Cleaned mildew buildup from the housing. Completed all other checks on the gas furnace per manufacturer recommendations. The system is currently working properly and efficiently. Optional recommendation left to improve indoor air quality (IAQ).