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Solution for whole house humidity problem, CT, Zone 5a

Jennifer M | Posted in General Questions on

Of the myriad home issues I have dealt with, the humidity problem is a constant.  While I am thankful that my house naturally falls into the 40-60% range in winter, in the summer it is regularly well over this threshold.  [I have written before about my incredibly leaky 1950’s ranch house.]

To control the moisture in the home currently, there is a Santa Fe dehumidifier running full-time in the plastic-covered crawlspace, and two Pure HEPA filter/dehumidifiers running on the main floor, along with a Panasonic WhisperGreen in the bathroom (all three running all day).  [The house is a 1400 sq ft ranch.]  There are two window air conditioner units, one at each end of the house.  All of this keeps us relatively comfortable and within the 40-60% humidity range.  However, it would be nice to ditch the dehumidifiers on the main floor.

In the winter, the windows are covered in “shrink wrap” and it is incredibly effective in terms of comfort.  The plan is to replace the windows (single pane with metal storms) after the Covid crisis, as well as add an ERV, which should take care of the humidity problem, along with other issues. 

Until then, would it help reduce the humidity to a noticeable degree if I put the shrink wrap back on the windows?  One window per room would need to be uncovered to allow for fresh air at night or on cool days; would the non-shrink wrapped windows defeat the purpose, or – as Martin pointed out in an article regarding a crawl space that could only have plastic on a portion of the floor – would the percentage covered basically equal the percentage of humidity reduced in the home?

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Replies

  1. Walter Ahlgrim | | #1

    Some things about your story trouble me.

    If your house is as leaky as you say and most 50s houses are I would expect to see the winter humidity readings to be 15 or 20%.

    Running exhaust fans 24-7 when the humidity is high outdoors than indoors is bring moisture into the house not removing it.

    Most window AC unit installs are far from air tight consider replacing them with a mini split system The DIY Mister Cool can cut out the HVAC contractors markup.

    The real question is where is all the moisture coming from?

    Has the home been tested with a blower door?

    Walta

    1. Jennifer M | | #2

      HI Walta,

      Yes, I've had a blower door test. If you click on my name, I think you can see a list of my questions here - to many of which you have provided great answers!

      No one seems to know why my home has so much moisture. After moving in several years ago, I excavated around the crawlspace and added a foundation drain, "tar" membrane over the cement block, and Roxul Comfortboard80 over that. Inside, the crawl floor and walls were covered with plastic, taped at all edges, and a Santa Fe dehumidifier was installed that has run constantly.

      The HERS rating was done after all of this.

      Eventually, I'll add an ERV with a heat coil (I really, really like the Minotair).

      So, the plastic on the windows won't be effective at stopping some of the humidity?

  2. Expert Member
    Dana Dorsett | | #3

    >"While I am thankful that my house naturally falls into the 40-60% range in winter,"

    Don't be thankful- be concerned. Anything over 40% in winter makes the house more susceptible to sheathing rot in CT's zone 5A climate, and probably leads to abnormally high mold spore counts in the indoor air during the early to mid spring time frame. Think of 40%RH @ 70F as the upper-bound target for the 12 coolest weeks of the year.

    That's a LOT of moisture for wintertime! In winter it could be easily managed by active ventilation. In summer it requires mechanical dehumidification, but the house materials can tolerate higher RH in summer, since the wood isn't accumulating the moisture from being too cold. The dew point of 70F/40% RH is about 45F, and the average temp at the sheathing in winter in your area is colder than that, so it will take up moisture. The dew point of 75% / 60% RH air is about 60F, and the average temp of the sheathing in summer is warmer than that, so the sheathing won't be taking on moisture.

    >"Until then, would it help reduce the humidity to a noticeable degree if I put the shrink wrap back on the windows?"

    Maybe, if leaky windows is the primary source of humidity in the house. But the high wintertime humidity numbers suggest there may be other humidity sources.

    1. Jennifer M | | #5

      HI Dana,

      The sheathing concern makes total sense. However, when we moved in several years ago, the siding was cedar shingle and the roof was flush with the sides of the house. We corrected that by adding a new roof with a 12" overhang (the pitch of the roof would not allow for more), and new siding (cedar clapboard instead of shingles). The sheathing looked beautiful, except in the areas of water intrusion. Before the siding went on, it was covered with Typar; behind the sheathing, there appeared to be a layer of yellow fiberglass-type insulation intact (against the plaster/drywall).

      I cannot afford to take off the siding again. Will going forward with an ERV and new windows solve this issue? I will be adding a Panasonic WhisperWarm in a bathroom down the hall; will these two Panasonic units, plus the range hood, do the job in my 1400 sq ft home?

      Perhaps I'll cover the windows this weekend (during the rain we're expecting) and see if it does help. The windows are incredibly leaky.

      Thank you!

  3. Expert Member
    Zephyr7 | | #4

    Something is probably leaky somewhere and letting humidity enter the home. What did your blower door test show you? Seal up the worst leaks first.

    An unsealed crawlspace can also let in a lot of moisture. When I sealed up my crawlspace (and I’m not even completely done yet!), it made a HUGE improvement in summertime humidity levels. It’s not fun work, but it makes a very noticeable improvement in comfort within the home.

    See if you can arrange things so that one of your air conditioners is running nearly continuously for maximum dehumidification. You’ll get better dehumidification performance with one unit running most of the time and the second only running when the first can’t keep up with cooling demand.

    A last thing to check: does your humidifier drain properly? If the condensate is not draining properly, it will evaporate back into the air and defeat the point of the humidifier. At that point, the humidifier is just acting like a small electric heater — costing you money but not accomplishing anything.

    Bill

  4. Jennifer M | | #6

    Hi Bill,

    We sealed our crawlspace with thick plastic, taped at all edges; excavated around the outside (see above for description); and added a dehumidifier. It's the coolest, driest room in the house!

    Good suggestion re: the air conditioners. I will leave one running at all times. And I'll make sure all of the dehumidifiers are working as they should.

    Thanks.

  5. Walter Ahlgrim | | #7

    Does water drip out of the window AC units when they run? Try catching the water in a bucket and measuring how much you get a day.

    How sure you are the instrument you are measuring humidity with is working accurately?

    I got to ask the silly questions sometimes people say yes anything like Pool, spa, aquariums or a marianna grow operation?

    Walta

    1. Jennifer M | | #8

      No water dripping out of the window ac units (they are Haier eco units, brand new this week). Humidity is measured by the Pure&Dry dehumidifiers, which need to be emptied every couple of days or so (the buckets). No extra water makers. Good questions! It seems that I may be measuring the humidity wrong by using the dehumidifiers, is that right?

      1. Expert Member
        Peter Engle | | #10

        If your dehumidifier buckets only need to be emptied every couple of days or so, then your house is already pretty dry. The dehumidifier setting might be dramatically inaccurate. Buy a cheap hygrometer or two and put them in centrally located places in the house to compare. You might find that the humidity is far lower than you think.

        Think of it this way. Your dehumidifiers are rated at xx pints/day. Look at the size of their buckets, and figure out if they are actually removing that much water, or just running all the time and not removing that much water.

        Another dumb question: Do you have them set to run the fan all the time, or do they cycle on/off when the setpoint is reached?

        1. Jennifer M | | #14

          The dehumidifiers cycle on/off, but once the dehum. cycle is off, the air filtration begins (same unit); in other words, a fan of some sort is always running.

          Excellent point re: the inaccuracy of the unit. I will buy a couple of hygrometers, as suggested!

    2. Robert Opaluch | | #12

      Walta,

      Each member of the family of 8 takes two long showers per day! Boil spaghetti for each meal. Laundry is dried on racks indoors, next to the wood stove's pile of logs! :-). Just kidding, sorry couldn't resist joking! :-) I apologize. You are not asking a silly question. It is possible there are some overlooked common sources of humidity indoors. Agree that the humidity is way higher than one would expect in winter, and cheap temp/humidity monitors are notoriously inaccurate with humidity measurements.

      This articles mentions various humidity sources and quantifies:
      https://www.greenbuildingadvisor.com/article/moisture-sources-relative-humidity-and-mold

  6. Expert Member
    Kohta Ueno | | #9

    I agree with all of the commenters above on trying to find the source of the moisture. Just to kick out another possibility--you mentioned that your foundation is concrete block, correct? Are they hollow-core block (I would expect so)? Any chance that the tops of the cores are open to the basement/crawl space? Pictures of the foundation interior might be useful.

    1. Jennifer M | | #15

      Yes, the concrete block is hollow. My plan is to fill the top of the cores with fiberglass insulation and caulk around this to seal (Martin wrote an article about this as some point). Thanks for the reminder to take care of this!

  7. Jon R | | #11

    > a Panasonic WhisperGreen in the bathroom

    Turn this off except when really needed.

    +1 on buying a good humidity meter.

  8. Walter Ahlgrim | | #13

    If your AC unit is running and working they are making water that must be going somewhere!
    Window units do try to evaporate some water outdoors but generally not all. But it has been years since I looked inside a window unit.

    I would not believe the sensors in the dehumidifier. I say buy 3 or 4 different makes and models of gages and believe the average.

    It is my way to ask the questions that must be asked in a way that is least unlikely to offend.

    Walta

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