Completed maintenance on attic system gas furnace. Checked all components for proper operation. System is in horizontal position with flue running out through roof, causing condensation to drip through flue pipe and into draft inducer. Cleaned orifice leading to pressure switch hose. Would recommend customer consider replacing this system due to its fair condition. System could be upgraded to a high efficiency system helping them save in their heating costs. Replaced filter, filter size 20x20x1. Cycled and tested, system working properly at this time.