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Community and Q&A

Water Leaking From Bathroom Exhaust Fan

emkingxx | Posted in General Questions on

Hello! We just had a new ductless mini-split installed on an interior wall. We have been using it for heating for about a month now. There is a small bathroom with an exhaust fan in the room directly behind the unit.

The other day, my husband and I noticed water leaking from our exhaust fan in the bathroom following a shower. Then this morning, my husband came and woke me up after his shower to see the ceiling. It is absolutely drenched, not just near the exhaust fan, but throughout the bathroom.

What could be causing this? And how do we fix it, quickly? I put the dry setting on the unit and left the exhaust fan on when I left for work, but clearly this is a major problem with the potential to cause irreparable damage.

I’ve perused the internet and all I could find are answers about the unit itself leaking or the area immediately around the unit having excessive condensation.


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  1. Jon_R | | #1

    I'd investigate "where does the water go if some exhaust moisture condenses?".

  2. Expert Member
    BILL WICHERS | | #2

    I would check how that bathroom fan is vented — it should be vented to the outdoors. Use the old tissue test too: see if a tissue will be held against the fan grille while the fan is running. The tissue should stay in place and only drop when you shut off the fan.

    I’d also check where the condensate line for the mini split goes and make sure it can drain ok. Condensate isn’t normally an issue when these units are in heating mode, but I’d check anyway.


    1. emkingxx | | #3

      Hi Bill,

      Do you think a very powerful exhaust fan would potentially be enough to solve the issue? I wish I was home to do the tissue test and had taken pictures this A.M. I was also looking into a dehumidifier in the bathroom itself, but it is so small that I'd really rather not take up the space.

      I also thought of maybe trying to run the "dry" setting on the mini-split while we shower, but I'm not convinced that would be long enough to make a difference.

      1. Expert Member
        BILL WICHERS | | #7

        If the exhaust fan is doing something wonky like just plowing into a joist cavity with no duct to the outdoors (I've actually seen this !!), then a more powerful fan might actually make things worse. You NEED that exhaust fan to vent the humid bathroom air to the outdoors, not back into the structure somewhere. That's what you really need to check.

        If you have an issue with the condensate line leaking into the ceiling (I've seen that too), then anything you do with the minisplit to try to dry things out will just pump more water into the ceiling since all the water the minisplit removes from the air becomes condensate that needs to go out the drain line.


  3. GBA Editor
    Kiley Jacques | | #4

    I'm going to put this puzzle to Jon Harrod. I bet he will have valuable insight. Stay tuned.

    1. Jon_Harrod | | #6

      I am going to echo the comments of Jon R and Zephyr 7. One scenario is that the fan duct got crushed during the heat pump installation, reducing airflow and allowing condensation in the duct before it exits the house. If the fan isn't flowing well, you may also get condensation on the cold ceiling. I have seen this happen a few times, where the entire bathroom ceiling turned into a condensing surface. Getting the ventilation working right and making sure you run it long enough (at least 30 minutes after a shower is what I recommend) will likely solve the problem. Dehumidifiers definitely have their place but are not a good long-term solution for bathroom moisture.

      1. Expert Member
        BILL WICHERS | | #8

        Good point about a crushed duct. I'd add to that and check that the fittings haven't come apart too. A good whack to a typical slip-fit duct can easily knock a connection apart, and its entirely possible that that could have happened without the installers of the minisplit even noticing that they'd caused a problem.


  4. kbtstone | | #5

    With the mini-split on an interior wall, where did they run the refrigerant and condensate lines? Could the installers have knocked off the bathroom fan duct by accident?

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