gas furnace water

I have inspected many regular gas furnaces and also many condensing furnaces but this is a first for me. On a vacant new house with a regular gas furnace, 60 degrees inside and about 60 degrees outside this morning, I turned on the furnace and after just a minute or so condensate water was pouring out of the A/C condensate pipe where it terminates into the laundry drain pipe. I went into the attic and the unit was spewing water out of all crevices and a large steady stream was running out the A/C condensate pipe. This was heat mode on a non-condensing furnace.

It stopped producing the condensation after about 10 minutes. I may not always be near the unit during the first 10 minutes but have never seen a wet furnace under these same conditions. Some of the condensing units leak inside and all and have various drainage issues but not these regular gas furnaces. I have decided that the exhaust must be partially blocked. Anyone seen this before?