Furnace maintenance in Braselton, Georgia. Three systems. Changed upstairs filter provided by customer and basement filter. Tested mechanical and electrical components. Found upstairs gas line drip leg not up to code, it isn’t long enough. Found gas line going into all furnaces not up to code, flexible gas line should not be inside furnace. Recommend making upstairs drip line longer and replacing flexible gas lines with hard pipe inside all furnaces to bring systems up to code. Brought all three gas lines up to code by moving flexible gas line to outside of furnaces, putting hard pipe inside furnaces and extending upstairs drip leg. Replaced main level flame safety sensor. Systems are heating at this time.