This is a brand new house and have had this problem from day 1. There is so much suction, or negative pressure, in the cold air duct that the water from the humidifier pad is actually being sucked in the duct and then I get a puddle of water at the base of the furnace. I have tried several pads hoping that one would be better than the other, but they all have the water sucked out of them. I am able to hold the pad at slight angle and see this happen, if I let go of the pad, it is sucked back into place. It is like they put too big of a fan in my furnace or the cold air ducts are plugged.
My water PSI is 60 and the requirement is that it be less than 125 so I am good there. I have also cranked down the supply line valve to the humidifier so I just get a trickle, and that helps, but doesn't totally solve the problem.
Is there anything else I can do to fix this?

  • 1
    A diagram would help us understand how the cold air returns, humidifier pads, furnace and hot air ducts all connect together. Feb 14, 2016 at 18:16

1 Answer 1


There should be a damper on the 6" pipe from the hot air plenum to the humidifier, closing it part way will help but the most probable cause is not enough return air openings in your house. If you have wall returns, take the grills off and make sure the air is going through and nobody forgot to cut the openings in the bottom of the wall or in the ductwork itself. Also get a copy of the heating design submitted in the building department to make sure it matches what's in your house, including the furnace size. It wouldn't be the first time a furnace was put in that was all they had in stock instead of buying the correct size. Mine was replace with one at double the btu output and I had to modify the orifices to half the output to get proper heating. High efficiency furnaces with too high of an output only wastes fuel since the design only brings them up to the proper efficiency after running for 20 minutes so you don't want it with a much bigger input than called for in the heat loss design. If everything is it's supposed to be and you closed the bypass damper and still having issues, you will need to add more returns in your house, even if it's a floor return grille in your return duct, or if the Return duct running down the sie of your furnce is under 10 to 12" on the narrow side and under 23 or 24" on the width, it should be changed to something around 10 x23" to 12 x 23", if it's still bad then you are really starving for Return airs!

  • I have closed the damper as well, forgot to mention that, but I fear you may be correct on the cold air return. There was some screw-up when house was built, they had designed a chase for the duct work to get to the 2nd floor, but they forgot about steel beam and they couldn't use it. The ran it through closest and changed the location of the furnace, they put it where the downstairs bath was roughed in (nice of them). Thanks for great answer, I really appreciate the help.
    – user49185
    Feb 17, 2016 at 14:35
  • Let me know what was wrong and happy you liked the answer, it's hard to solve these troubles when I can't see it but you have enough knowledge of what went on at least. Good Luck!
    – Richard
    Feb 17, 2016 at 15:19

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