I have water leaking from underneath my funace. I have A,C. but it is not on. The amount of water is about a gallon a day. I have isolated The A. C. drain line from the furnace and I am still getting water leaking from underneath. I opened the front of the funace and there seems to be a little water on the base plate below the intake and outtake air ducts but not near the amount that is leaking. This is a natural gas furnace. What's up??

Is this a condensing furnace? Drain to the condensate pump or other drain could be plugged. Exhaust pipe could have a sag in it and water condenses and runs back to the furnace.