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Community and Q&A

LG Split HVAC with dehumidifier

Rhonda Carpenter | Posted in PassivHaus on

We built a PassivHaus with a Silver rating. We are in the South so it is hot and humid. We have a mini lg split with a dehumidifier and an ERV system on our 2200 sf home. We have been in the home for 4 months now and cannot get the humidity under control. It is currently between 71-80% at any given time. Seems to increase when we turn on the dehumidifier (80%). Our smoke alarms have started to go off when it gets that high. My shoes have molded and the sheetrock tape is bubbling off. The temperature in the house is lovely, but it feels and is wet. We do not have any condensation in the house. We FINALLY have an appt with the contractor who installed the system. What is going on here? I want to be armed with as much knowledge as I can before they come. I hope I have provided enough information.

Thank you.

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  1. Steve Knapp CZ 3A Georgia | | #1

    Rhonda. Where in the south exactly? Was the house exposed to the elements during construction? What type of foundation do you have? What type of ventilation system do you have? What does your HVAC contractor say about the humidity issue?

  2. Rhonda Carpenter | | #2

    We are in the piedmont region of NC. Yes, it was exposed to the elements. We have a concrete slab foundation (and exterior walls). In the foundation is gravel, styro insulation, and concrete (all ~2 ft deep). We have an ERV system with duct work (that's really all I know). Our appt with the contractor has not yet happened. They were not returning calls or emails. It has been quite the ordeal.

  3. Steve Knapp CZ 3A Georgia | | #3

    Others will comment I'm sure. If I were you, I would buy an inexpensive EnergyStar dehumidifier and run it to bring down the humidity. That will give you more breathing room to sort out why your home is not performing well. High humidity in a tight structure is risky. Once mold and mildew are established, they can be hard to eliminate.

  4. Rhonda Carpenter | | #4

    Thank you Steve. I appreciate the advice and agree.

  5. User avatar GBA Editor
    Martin Holladay | | #5

    As far as I know, there is no such thing as a Passivhaus with a Silver rating. The "Silver" designation must refer to a different program (not Passivhaus) such as LEED for Homes.

    What brand of dehumidifier was installed?

    Is it a stand-alone dehumidifier or a ducted dehumidifier?

    Where is the dehumidifier located?

    Are you emptying the dehumidifier bucket by hand, or it is connected to a drain?

    If you are emptying the dehumidifier bucket by hand, about how much water is collected daily?

  6. Jimmy Nguyen | | #6

    Hi Rhonda,

    I posted about this very issue just yesterday too. I have an LG minisplit and you can run it in dehumidify mode. It's the little rain drop icon when you click through the mode button on your handheld thermostat. When I run it in this mode - the humidity can get down to as low as 52%. It usually stays in the upper 50s. However, it does mean your house will be a bit cooler. When running in dehumidify mode, my house gets down to 72 degrees. It may cost you more to run it in this mode too. Check out this old thread about this issue in HVAC talk -

    Someone suggested that right-sizing the indoor units would solve the problem. Others said that this is a normal problem with minisplits because they are built to run constantly and some of the moisture from the evaporator coils is put back into your indoor environment from the continuously running fan. An expert like Dana may be able to answer this definitely. I'm actually going to call LG tech support today and can you everyone an update on what they said.

  7. Rhonda Carpenter | | #7

    Martin, you are correct re: our house is not a passivhaus silver. We did get a LEED Silver rating ....just trying to let everyone know it is passiv and was tightly built, etc. Sorry for the confusion.
    We have LG Split HVAC w/ Dehumidifier ducted and connected to a drain. I think the location is in a spot above 2 closets.

    Jimmy, when we run the dehumidifier, the humidity goes up and the smoke alarms go off. The humidity in the house has never gone below 71%. Thanks for the thread. I called LG and was told that my dehumidifier will not get the humidity down to normal due to it being so high and that this was not what they were for. What??? They were of no help. Perhaps I should call again and get another tech person.

  8. Steve Knapp CZ 3A Georgia | | #8

    Rhonda. Perhaps your home was built to the Earthcraft Silver standard. If so, find out who rated and certified your project. The builder should have provided paperwork showing that your project met minimum requirements for that level of performance.

  9. User avatar GBA Editor
    Martin Holladay | | #9

    The minisplit manufacturer (LG) was correct when they told you that just because your minisplit has a "dry" mode does not mean that your house has a dehumidifier.

    Your house does not have a dehumidifier. It has an air-to-air heat pump with a "dry" mode, sometimes called a "dehumidifier" mode. This appliance is not a dehumidifier.

    Go out and buy a dehumidifier. They cost $250. In a couple of weeks, everything will be better.

  10. Rhonda Carpenter | | #10

    Martin, I am on it! I can't lose any more shoes! Thank you all for your help!
    Steve, I have the certificate somewhere!

  11. Rhonda Carpenter | | #11

    I will post again once the contractor comes out in a couple of days. I think it is crazy that we have to buy another device to control the humidity. Why wasn't this thought of before??? It's not our contractor's first day. It was certainly my first day building this home, but not his!

  12. User avatar GBA Editor
    Martin Holladay | | #12

    I don't know much about the expertise of your builder or the expertise of your Passive House consultant (if indeed you had one).

    But it is fairly well known that tight homes in your climate will need a dehumidifier, at least during the first year of occupancy, to handle construction moisture.

  13. Rhonda Carpenter | | #13

    Martin, he is a certified green builder. I hear what you are saying though. The builder seems perplexed about this issue. I don't think it has helped using green wood inside the house...from the trees cut down on our property. I think that was a big mistake! I have learned many lessons. Apparently, still learning them.

  14. Steve Knapp CZ 3A Georgia | | #14

    Rhonda. My builder was a certified Earthcraft builder, and I imagine yours is as well. That certification and a dollar will get you a cup of coffee. Some builders are more into the marketing than the science. If he is "perplexed," I think your guy is definitely in the former category.

  15. Rhonda Carpenter | | #15

    The builder is guessing that the mini needs refrigerant or makeup damper is stuck open, or something to do with the ERV. The builder and contractor will be out there tomorrow.

  16. User avatar GBA Editor
    Martin Holladay | | #16

    The ERV cannot be used to lower indoor humidity levels. If the weather is hot and humid, then operating your ERV makes the situation worse indoors -- it raises the indoor relative humidity. The more you run the ERV, the worse things get.

    You should minimize use of your ERV during hot, humid weather. You want the least amount of mechanical ventilation consistent with occupant comfort and health.

  17. Rhonda Carpenter | | #17

    My builder did say to not turn on the ERV in the bathrooms. We have done that.

  18. User avatar
    Dana Dorsett | | #18

    Seriously, when outdoor dew points are in the mid- 70s F it's time to turn the ventilation to it's minimum rate, or even completely off, to let the AC & dehumidifiers dry out the place. You'd still want to use exhaust ventilation for the kitchen & bath while in use, but the latent load you're letting in with ~75F ish or higher outdoor dew points is huge, even with an ERV cutting the load in half.

    Unless there is a requirement that the ducted system have outdoor make-up air, closing the damper is the right thing to do. If that were your only ventilation that might not work, but if it's pulling in air every time the air handler is running it's adding moisture to the house when it's sticky outside, not removing it, and the hotter it gets outside, the more humidity it's pulling in due to the higher air-volumes or duty cycle.

  19. Steve Knapp CZ 3A Georgia | | #19

    Do you have Panasonic ERVs by any chance? Are there exhaust fans in the bathrooms?

  20. Rhonda Carpenter | | #20

    Dana, thanks for the information. Steve, I do not know the brand of ERV, but I will find out. The ERV system is in the bathroom (from what I understand). We can set it for 3 hours or less.

    More to come tomorrow.

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