My laundry floor is soaked but I can’t find a pipe leak anywhere! 

I don’t believe you have a pipe leak. I think you’ll find that the water is coming from the bottom of your furnace because the air conditioner ‘A’ coil drain is blocked. “What is an A coil drain?”

The A coil (which is like a car radiator shaped like the letter A) sits in the air delivery duct just above the furnace. This evaporator coil is used for air-conditioning. When operating, it gets very cold and the air flowing over it and through the duct becomes cooled. The sudden drop in temperature causes the air flowing over the coil to give up its moisture (cold air does not hold the same amount of moisture as warm air). The moisture then runs off the coil into a drain pan and is transported through a plastic pipe to the floor drain. The more humid the day… the more moisture released!

Unfortunately furnace filters do not capture all of the finest dust. Some of this settles on the A coil and is flushed off when the air conditioner is operating. Usually this dust is just flushed down the drain. However, over time the dust can accumulate in the plastic drain pipe; eventually blocking it. Now the only escape the water has is to flow over the top of the evaporator tray and down inside the furnace, to exit on the floor.

You can overcome the problem by finding where the drain pipe exits the furnace duct. 

Usually there is a half inch plastic pipe that goes to the floor drain. Just above the pipe you’ll find a plug and this is at the level of the evaporator tray. So, by removing that plug, you can clean any debris out. Blow through the plastic tubing from the outlet end to discover if you have a blockage. If there is blockage you will need to remove the plastic pipe and blow it out.

this point you have overcome the problem of a blocked drain and your floor will dry out! But, be very careful; the water that has leaked At down inside the furnace could have caused an electrical short or rusted out the heat exchanger. Be certain that all electric wiring and contacts in the furnace are dry and the heat exchanger is good repair before attempting to start the heating system.

It may be a very good idea to call in an expert to do this job for you!

Doug Hastings
MN Home Inspector, Minneapolis & St. Paul
ASHI Certified Inspector, ACI
Kaplan University, Home Inspection Lead Instructor

Rob ‘Pops’ Leslie
Kaplan Professionals, Retired