The Great Humidity Mystery


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Old 05-24-23, 11:20 PM
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The Great Humidity Mystery

Hi all,

I live in an apartment and we have some really strange humidity problems. The humidity in the apartment tracks with the weather-- a few hours before it rains and for several hours to a few days afterward the humidity will spike into the 60s or 70s. Two years ago we had a moldageddon, and that's when we realized it.

The apartment management can't figure out what's going on and neither can we, so we have been running a dehumidifier. None of the other apartments have a problem. We found a leaky window using a flir and stopped it up, but the shifts are still dramatic when the weather changes. Any ideas for where we could look? When it isn't raining we don't have issues with cooking, dishes, etc. significantly adding to humidity -- it has to do with the weather but we can't figure out where it's coming in.

Thanks in advance!
 
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Old 05-25-23, 12:23 AM
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The humidity in the apartment tracks with the weather
Its perfectly normal for the air quality (temp/humidity) in a structure, assuming it's open to the exterior, to match the external air conditions so that does not seem unusual. Is the structure "conditioned" (heating/cooling/humidified/de-humidified) such that your not able to control the temp/humidity?

That would seem to indicate an equipment issue.
 
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Old 05-25-23, 12:32 AM
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Thanks! Yes we have central air, and maintenance investigated the HVAC and it was normal. What's especially weird is that when it rains the humidity goes up, but often higher than outdoors? Before the dehumidifier, we literally had mold growing over all our shoes, books, etc and had to throw a number of things away. Even running the dehumidifier unit we struggle to keep the humidity down at residential levels. None of the other apartments in the building have issues with humidity. What sort of equipment issue might amplify outdoor humidity for one apartment?
 
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Old 05-25-23, 04:49 AM
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When the air conditioning runs does it seem to run in short bursts or does it come on and run for a longer time with a long off period in between. Much of the time it should only run a few times an hour and maybe run for 10+ minutes. That allows it to run long enough to remove the moisture from the air. If the system is oversized it may only run for a few minutes which gets the home cool but doesn't allow enough time to remove the humidity.
 
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Old 06-01-23, 07:34 PM
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Thanks! It runs for about 10 minutes or so a few times an hour-- could there be something else?
 
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Old 06-02-23, 12:35 AM
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but often higher than outdoors?
Is the humidity actually measured or is ti just an assumption? The humidity both inside and out should be the same unless there is some conditioning taking place that lowers the inside "conditioned" air. If it is actually higher then there has to be something that is forcing the level higher like a water leak or something that adds humidity, like showers, an un-vented dryer, cooking, even large number of plants. Should be something obvious to identify!
 
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Old 06-04-23, 10:08 PM
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Thanks! We have a little hygrometer in each room, so it's measured. This weekend it clocked 68% indoors, and it was 67% outdoors. When we cook & do laundry it bumps up 1-2% but when it's about to rain and the humidity goes up outside it can jump 15-20% very rapidly and that's when we start getting mold. We found a leak in one window where you could see a trail of mold blowing in, and stopped that up, but we can't figure out why we are the only apartment with such high humidity :/ No plants bc voracious cat beast
 
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Old 06-08-23, 10:31 PM
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An update: we are in the wildfire smoke and our particle counter shot up indoors despite no open windows, filtered HVAC, air purifiers running and not opening the exterior doors. It makes me wonder if our humidity issue has to do with a leak in the windows or something. How would I track down a window leak? We have a FLIR because we are nerds and found one leak last winter using it, but not sure how in summer
 
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Old 06-08-23, 10:41 PM
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They use a candle to detect air movement!
 
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Old 06-09-23, 04:44 AM
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The FLIR will need a temperature difference to tell you anything. You might spot something on a hot day with the AC on but it won't show as clearly as in winter when the temperature difference is much greater.

You can use smoke. Either a smoldering cigarette or blown out match. Just make sure the AC has been turned off for at least a few minutes and you let the air settle down from walking around. It works best if you test on a windy day. A candle can also work like Marq mentioned.
 
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Old 06-09-23, 06:41 AM
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Thanks all! Is there an alternative? I'm deathly allergic to smoke, and we can't have open flames.
 
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Old 06-09-23, 08:55 AM
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If you want to spend money there are air flow fog machines ($35 Amazon) that produce a fog similar to used in nightclubs and plays. I think the liquid used to make the fog is glycol and glycerin which I believe is not an allergen though I suppose it could trigger asthma if you are quite sensitive.
 
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Old 06-09-23, 09:58 AM
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Thank you! How would I use that-- do I bring it outside and see what comes in, or put it next to the window and see if it moves?
 
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Old 06-10-23, 06:39 AM
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Is there a make-up air vent someplace? Perhaps connected to the return of the furnace/air handler? (This was done years ago) Someplace outside air is being pulled into the building.
 
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Old 06-10-23, 08:37 AM
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Thanks Tolyn! What would that look like? Our HVAC closet is locked, would I be able to tell without looking in it?
 
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Old 06-11-23, 06:15 AM
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Does your apartment have its own furnace/air handler? Do you have your own water heater or is that provided by the building? What state are you located in?

Usually, there will be a vent on the outside of the building or roof that runs into your apartment, into the mechanical room, or runs directly into the return of the air handler/furnace.

Do you have an exhaust vent over the stove that vents outside or does it just recycle the air in the kitchen?
 
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Old 06-29-23, 07:23 AM
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Okay I've done some investigating. I'm not sure what exactly is in the HVAC closet, but we do have a shared boiler. There are little vents on the roof above each top story apartment. Our stove seems to just recycle air but does not have a carbon filter so I'm not sure.

One thing I can say is the wildfire smoke is back and our indoor particle counter has jumped WAY up. Something is definitely letting air in and not filtering/cycling it back out.
 
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Old 07-12-23, 03:08 PM
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Okay, back with more data! Three days ago it rained, so I grabbed 3 snapshots roughly 24 hours apart. You can see how the humidity jumps up with the rain, but then never comes back down again. We are running a 50pt Honeywell dehumidifier in the living room (IN) and it fills up and we have to empty it 3x/day to keep the levels even just in the 60s, we can't seem to get it lower. It's only a problem in the summer. Any ideas?



 
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Old 07-12-23, 03:53 PM
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I didn't see it anyplace in this thread, what is your location? (State/City) Can you post pictures of your HVAC system? Is the boiler for heat, hot water, or both?
 
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Old 07-12-23, 04:19 PM
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I'm in MD, and the HVAC is locked in a closet so I'm afraid I can't give a picture. I don't know if the boiler is for heat; they did mention something about the heat being in the HVAC once, and it gives that burning-hair smell when we turn it on in the fall (so not a steam system.)
 
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Old 07-12-23, 06:45 PM
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I would assume you have central air conditioning correct? Or is it just a window unit?
 
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Old 07-12-23, 09:19 PM
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Yes that's correct-- central air with a thermostat
 
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Old 08-16-23, 09:12 PM
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Just wanted to check and see if y'all have any thoughts. We are emptying our humidifier 3-4 times per day and struggling to keep the humidity below 70%
 
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Old 08-17-23, 12:53 AM
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we have to empty it 3x/day to keep the levels even just in the 60s, we can't seem to get it lower. It's only a problem in the summer. Any ideas?
IMO there is no problem this is just a normal situation, warm summer muggy weather, higher humidity levels, doesn't seem any more unusual than what I experience around our MI home & basiement in the summer.

 
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Old 08-17-23, 04:32 PM
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Sadly without actually seeing it, I am out of ideas.

The only suggestion I have is to call an HVAC company on your dime and have them check out your equipment and situation. This company should not have any affiliation with the building/property management.

 
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Old 08-30-23, 04:58 PM
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Thanks all. I've lived in humid places all my life too but have never had to throw out everything I own that's organic because the entire house is growing mold. It rained yesterday and the humidity jumped, but today the exterior humidity is 47% on our meter and 83% indoors. It's definitely not the great outdoors, or indoor appliances; we are the only apartment with this problem. And sadly our HVAC closet is locked so we can't even look in it ourselves. If y'all think of any other ideas I'm game
 
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Old 09-17-23, 12:03 PM
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we struggle to keep the humidity down at residential levels.
I think residential levels vary widely, depending on outdoor humidity as well as indoor activity such as cooking, showering/bathing, washing clothes, opening doors to outside, etc.

I'm a fanatic of sorts about monitoring both the outdoor and the indoor temperature as well as indoor humidity levels. It's kind of like a hobby to me! I have numerous thermistors to sensor and measure the indoor and outdoor temperatures, including even the temperature in the attic! And I also have multiple hygrometers to measure the indoor n outdoor humidity.

I've noticed two things about the indoor humidity level:

(1) The hotter it gets outdoors, the lower the outdoor humidity gets. Here is the Dallas area the humidity can plummet from 97% down to 25% on a day that starts out with a high dew point and very humid and then gets up to 100+ later in the day.

(2) I found that typical of all sensitive hygrometers is that it doesn't take much to really increase the humidity measurement. I can casually breathe out one time from 12" away and within a few seconds the humidity will increase 8 to 10%. If I put my hand within an inch of the device without actually touching it it'll increase 5% or more.

Below is a picture I took recently of a Hygrometer/Temperature monitor with convenient magnets on its back attached on a return air vent. When I took the picture it was a typical 100+ summer day. Notice the 12% humidity range of 45% to 57% - it literally jumped about 10%+ by me just touching the monitor with my hand for a few seconds.

 

Last edited by Kooter; 09-17-23 at 12:52 PM.
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Old 09-17-23, 01:31 PM
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It's a great point! Do you have a good sense for how to track down where humidity might be coming from? I can't currently close the guest bath door because it's so swollen, and I can close other doors that sometimes swell up, so not sure if that's a sign of some sort. I really don't want to have to lose my library to another moldageddon -_- I'm in the Mid-Atlantic so humidity is kind of a given, but I've lived here all my life and never had this problem with consistent high humidity to the point of doors not closing and mold on clothing before.
 
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Old 09-17-23, 03:15 PM
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tetrapteryx - Just a guess, but I'd look into the source of your high humidity coming from below - from the ground, not coming from within your apartment, or coming from the ambient outside air penetrating through your walls or coming from windows.

What level is your apartment on? How high above ground level are you? Do you know anything about immediate surrounding area; like if there are high water tables or underground creeks/streams or culverts nearby or under the building?

I had a friend years ago that owned a condo in which an underground stream or vein of water flowed under his building. The underground water vein was thought be to about 20 feet deep underneath his building, but surfaced to ground level some few hundred yards away.

With none of the other apartments having this same problem you do, that is likely a clue that in some way your apartment location is somehow different. Is the other apartments not having this same problem you have pretty much a fact, or just supposition?

What you are describing is indeed mysterious, but like most mysteries there's usually a transparent explanation once the onion layers are peeled away.
 

Last edited by Kooter; 09-17-23 at 05:00 PM.
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Old 10-11-23, 08:49 PM
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Thanks again! I return with more information!

We are several floors above the basement, and several floors above ground level.

We gave our next door neighbors one of our little humidity monitors, and their humidity hasn't gone above 60, despite similar work from home schedules as us, similar cooking, dishwashing, etc.

We have 2 different kinds of hygrometer in the apartment because it seemed so ludicrous we wanted to double check.

Today the humidity outdoors was 30% and still pushing 80 indoors, so we opened the windows to vent the humidity, and it dropped way way down. Within 3 hours of our closing the windows, the humidity was back up near 80% in the main bedroom/bath, which we had not entered after closing the window. The door to that bedroom stays closed to exclude the cat, and it is always the most humid. Last fall, I found some kind of mildew growing in an airflow pattern in a bottom corner of the window casement and used foam and caulk putty to seal it.

What is the mechanism by which an apartment vents humidity? Could there be something wrong with our bathroom vent that's letting humid air in?
 
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Old 10-12-23, 04:58 AM
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"...bathroom vent that's letting humid air in?"
Since it sounds like the outside humidity tends to be lower than the inside, if air were flowing in via the vent it would be to your benefit and lower the humidity inside your unit.

Humidity leaves by direct air exchange. Essentially air leaks like the one you sealed. Much also passes through the walls.

Since you've tried so many things I would wait for a nice cold spell that will have rain and rent or borrow a thermal (FLIR) camera. Turn on the heat inside. Then go through the apartment looking at all the walls & ceilings. Water and air leaks will be quite visible and may give some clue to where all the moisture is coming from.
 
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Old 06-06-24, 06:06 AM
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Solved!

Hi all!

I wanted to thank you again for all your help and let you know the answer, as we just found it this past week!

Turns out that the sealant on one of our windows was old, and when it rained or got damp created a reservoir that kept the apartment humid and caused gunk to grow in and leak from the casement. Management had the window re-sealed, and instantly the problem was gone! I didn't know it could work that way, but you learn something new every day.

Thanks again!
 
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