GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Cooktop/cabinents and mildew problems

GBA Editor | Posted in General Questions on

Our house is 2 years old. We have never had problems before, but in the last 2 months our cabinets under the cooktop and down draft have collected ALOT of moisture and mildew. It is so much, I now have to leave the doors open all the time. My contractor does not know why. Does anybody have any help or suggestions. We spent a ton on our cabinents and I dont want them rotting away! THANKS so much!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Where are you located? Is the problem you describe worse in the summer or the winter?

    It is possible that the downdraft fan is depressurizing your kitchen, and that cracks under your base cabinets are allowing the entry of hot humid air into your home. But I'm just guessing.

  2. HDendy | | #2

    Maybe there's a leak in the downdraft flue/piping under there that's creating just a negative within that base cabinet and pulling moisture from cooking into it from cracks around the cooktop. Depending on the material and finish of the cabinets they could be fairly impermeable and trapping the moisture. Or, the fan is pulling more air than it can exhaust through the wall penetration and some is backing up into the cabinet. Check that the damper on the outside is functioning.
    I saw some slides a while back of moisture/mildew problems behind cabinets because the backs were acting like an interior vapor barrier, but that's not exactly what you're describing. While you're figuring it out you can put damp-rid in there to help absorb the moisture, that's just a band-aid though.

  3. Danny Kelly | | #3

    Stacy - since you have a downdraft, I assume you are on a crawl space. Your moisture is probably coming from there. Martin is probably correct - when running the downdraft, there is a slight negative pressure in your cabinet box so it is bringing in air from the crawl. Quick fix may be to go in the crawl and seal very well between the downdraft duct and the subfloor with some spray foam. Also, check the seams in your duct and make sure they are not leaking. Most contractors will not seal the joints in these systems since they are not pressurized the same way as a HVAC supply duct would be but is good practice - seal all joints with mastic.

  4. NShawhan | | #4

    Following to see if you get an answer. I had to read it twice to be sure my husband hadn’t posted it because our situations are identical. Two-year-old house, and can’t say if it’s worse at certain times of the year because it just started. We are in South Louisiana, and not on a crawl space; a pipe runs through the slab to the outside. It doesn’t seem affected by how much or how little we use the vent, and we actually have not used it much lately (been doing more outdoor cooking.). Closing the cabinet will result in dampness on the insides of the doors in just a few hours. A hanging moisture eliminator has an inch of water after two days. Also, our dryer has started doing the same thing... wet on the inside of the door, wet lint in the lint trap, damp clothes if left overnight. We resealed all the vent connections under the cabinet with foil HVAC tape but to no avail. Any thoughts?

    1. Expert Member
      MALCOLM TAYLOR | | #10


      Just to be clear, your ducts run under the floor slab in the fill, and out through the f0undation wall?

    2. beachreader | | #12

      Did you have any luck fixing your dryer vent? We’ve had the same problem and haven’t been able to improve it yet. I’ve cleaned the vent out many times, checked the damper, etc but still has condensation. I’m going to try to tape up my downdraft tomorrow.

  5. tommay | | #5

    When you cook food you remove it's water, when you boil something you create water vapor...not to hard to figure out where the moisture is coming from......are your pots and pans higher than your down draft fan? Try using covers or lids when you cook.

    1. NShawhan | | #6

      Tom May, Thanks for the reply. It’s definitely not a cooking steam issue. As I mentioned, we’ve barely used the range in the past couple weeks, because we’ve done mostly outdoor cooking, and it’s happened every day during that time. We haven’t used it at all for the past 4 days, since we discovered it, and if I close the cabinet doors for a few hours the insides of the doors will be wet.

      1. Expert Member
        Akos | | #7

        Sounds like an air leak. Most likely the damper on the range hood vent is also not sealing well.

        Since both the rangehood and dryer vent are near the bottom of the house, stack pressure is drawing in outside air through them. Once this outside air hits the colder surfaces in the house, it condenses causing your issues.

        The best solution is to air seal around the vents as well as all the seams on the ducts. Make sure the damper on both vents is working/clean.

        1. NShawhan | | #8

          Akos, sounds like good advice. We will try that today! Thanks!

      2. tommay | | #9

        I misread your comment, I thought it was a cabinet above your cook top. You say they ran the vent for your cook top and your dryer in the slab. In all my years I have never seen that done. What type of piping material did they use to do this? Hopefully you are not getting water into these lines either from the ground or from condensation from humid outside air being cooled as it passes through the piping in the slab from the stack effect as Akos mentioned. The height of the vents above the slab going to your appliances seems like it would not create to much of a draft especially in a closed cabinet and closed dryer door, unless there is something in your house creating a negative pressure causing the vents to draw air in which could be something as simple as an open window or skylight or exhausting fans. Are their dampers or flaps on the outside of the house on each of the vents that may be stuck open?

  6. beachreader | | #11

    I feel like you are writing about my house too!! I have the same problem with our downdraft and now our dryer vent as well. We are also in Louisiana, but in the NW. the downdraft is through a slab and creates all kinds of condensation / humid air inside the cabinet and some days in the whole kitchen. The clothes dryer vent runs up through a wall and out through the roof but has had a great deal of condensation lately, even fog and water droplets inside the dryer.
    Did either of you get a solution to your problems?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |