Cleaned & checked gas furnace. Inspected heat exchanger & flue venting. cleaned burners & flame sensor. Checked voltage & amp draw of motors. Test capacitor. Found basement pressure negative (-.005 inches water column) due to leaks in return-air ducting and return air vents blocked by curtains and dirt. Moved curtains. Adjust Blower: 3.0A . Inducer: 1.0A . Adjust Gas pressure: 3.6 inches water column. Temperature rise:48 . Supply: 115 . Return: 67. Basement: <-.001”. Suggestions: clean return air vents and keep curtains away from return air vents. Humidifier: $716