Ask the Carpenter: Dealing with a leaking humidifier

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Q. A few years ago we added a humidifier element to our furnace. It was fine the first year, but now it leaks. The water appears to be coming from the seams on the bottom where the plastic housing would snap in. We have had our local heating, ventilation, and air-conditioning company come out three times. The latest “fix’’ is to replace a part of the frame that may have a hairline crack. The leakage lessens when we turn the humidity control down, but then we aren’t able to set the conditions in our house the way we’d like. Have you run into this problem before? Do you have any recommendations?


A. I reached out to my friend Joe Morris, an HVAC specialist. Joe told me that if it’s a “bypass humidifier,’’ someone might not have changed the humidifier panel, and instead opted to turn down the air intake (also called a bypass), making it leak less. This would be a rookie mistake.

Changing the panel should be part of your yearly maintenance; it gets clogged with calcium and water deposits. Once the panel gets clogged, it can drip into the ductwork.

He suggested having the lead technician, maybe even the HVAC company’s owner, come out to troubleshoot and clean the unit, replacing all of the parts the manufacturer recommends. Additionally, have them set the bypass to zero, the original setting, and see whether this resolves the problem.

Cracking? On this theory, Joe is skeptical, because there are no screws in these units to be overtightened, causing it to crack.

Rob Robillard is a general contractor, carpenter, editor of, and principal of a carpentry and renovation business. Send your questions to or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at