High humidity

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Old 10-07-17, 12:42 AM
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High humidity

We have a new (less than a year old) 3-ton central A/C system (Lennox). We had a hurricane a few weeks ago and the power was out for a few days. No damage, but we're noticing salt shakers clogged and clumped. At first I thought it must have been due to the couple of days without A/C but then we realized some fabrics feel almost damp. So I started checking a hygrometer several days ago and it looks like humidity is varying between 70% and 80%. Last time I noticed (probably around June or July) I'm pretty sure it was holding at about 40-50% unless a door was open.

Cooling temperature is fine and consistent. Is the humidity problem likely to be an A/C mechanical problem and what would cause it?
 

Last edited by suobs; 10-07-17 at 01:02 AM.
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Old 10-07-17, 01:36 AM
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Is the AC working? Humidity is relative to AC temp, as the air cools water is removed.
 
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Old 10-07-17, 02:05 AM
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AC generally reduces the humidity within a few days of running. I lived in fla a long time ago without AC and while the humidity was brutal I don't recall any fabrics feeling damp. Are you positive no rain got into the attic? insulation can hold moisture for a long time.
 
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Old 10-07-17, 03:17 AM
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Today, 04:36 AM #2 (permalink)
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Is the AC working? Humidity is relative to AC temp, as the air cools water is removed.
Yes AC is working fine and cold. What you say is the way I thought it worked - you're saying there is no separate component that removes moisture, it's part of the cooling process, right?
 
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Old 10-07-17, 03:23 AM
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AC generally reduces the humidity within a few days of running. I lived in fla a long time ago without AC and while the humidity was brutal I don't recall any fabrics feeling damp. Are you positive no rain got into the attic? insulation can hold moisture for a long time.
Hm, you may have called it. We did lose a few shingles and noticed just last night a small leak that was in dripping onto the ceiling insulation. I am currently catching the drippage in a container above the insulation until roof repair.

Sounds like the best course is to check to see how wet the insulation is and replace it if wet and keep water off it until I can stop the leak?
 
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Old 10-07-17, 03:55 AM
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What you say is the way I thought it worked - you're saying there is no separate component that removes moisture, it's part of the cooling process, right?
Sometimes a dehumidifier is added to the HVAC system but it's not a standard item.

Sounds like the best course is to check to see how wet the insulation is and replace it if wet and keep water off it until I can stop the leak?
The sooner you remove the wet insulation the better!
 
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Old 10-07-17, 06:53 AM
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When a house is being cooled that air is heavier than the warm air outside so it pushes out the lower portions of the house and is replaced by air from the upper portions, ie the attic. All houses experience a lot of air exchange so what ever is up there is what your ac has to deal with in the house.

If enough water got in it is working its way through your insulation and may get to the drywall which gets more expensive.

Bud
 
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Old 10-07-17, 08:26 AM
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If enough water got in it is working its way through your insulation and may get to the drywall which gets more expensive.
Already got to the ceiling drywall. Just a small patch though.
 
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Old 10-07-17, 08:38 AM
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So is there a consensus that this is probably being caused by a small area of wet insulation/drywall in the attic? Not an AC problem? Obviou$ly I don't want to bring in the AC guy$ if I don't have to although they $aid something about a relay $witch.

When I first bought the hygrometer I found it interesting (I must have had fewer projects going then) that I could sit upstairs watching it and when my wife opened a door downstairs I would see the humidity change within a couple of minutes. And that was in the winter when outside humidity is fairly low.

Even so, I'm not sure I see how wet insulation in the attic increases humidity in the house. Granted there's wet drywall, but it's mostly in the attic, not the house. Not like an open door or window. I mean the attic is super-humid most of the year in Florida anyway.
 
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Old 10-07-17, 09:29 AM
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Is your upstairs ductwork in the floor or ceiling?
 
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Old 10-07-17, 09:41 AM
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@suobs "Even so, I'm not sure I see how wet insulation in the attic increases humidity in the house."
That is what I was explaining. I do energy audits and we deal with natural airflow into and out of a house. During summer conditions when the ac is running the air inside your home is leaking out the lower area and being replaced by air leaking in from above. Design standards allow homes to exchange ALL of the inside air every 3 to 4 hours and in your case most of that air is coming from the attic. Spray a strong perfume up there and see how long it takes for you to smell it throughout the house. Or search "reverse stack effect for another explanation.

Take a humidity reading up there along with the temp at the same time. Use an online calculator to determine the dew point. Use that dew point and your inside house temp to calculate what the humidity reading for the air coming down from the attic.
Temperature, Dewpoint, and Relative Humidity Calculator

Bud
 
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Old 10-07-17, 10:35 AM
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Today, 12:29 PM #10 (permalink)
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Is your upstairs ductwork in the floor or ceiling?
The ducts are in the ceilings. I should add that the roof is multilevel for a vaulted ceiling, and there are three attics, one first floor over the kitchen where the leak is, one above the second floor (these two are connected), and one above a inlaw apartment that is entirely separate but attached to the house. The whole house is on the one AC.
 
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Old 10-07-17, 10:42 AM
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IF there are any leaks in your ductwork it can draw moist are and bring it into the house. Also any metal connections that aren't well insulated can be an issue.
 
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Old 10-07-17, 01:00 PM
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During summer conditions when the ac is running the air inside your home is leaking out the lower area and being replaced by air leaking in from above. Design standards allow homes to exchange ALL of the inside air every 3 to 4 hours and in your case most of that air is coming from the attic.
I can see that. What I'm not getting is how a patch of wet insulation would increase the humidity in the attic significantly. Humidity is high up there anyway, I would say in general it's exactly the same as outside, typically >80% in summer when it's not raining. That's normal so it doesn't seem to explain my problem. Unless something changed recently like I left an attic access open increasing the leaked airflow coming directly from the attic, or there's a new hole in the ductwork, I don't see how it would change much what is pulled into the house by leakage, compared to a few weeks ago.

Take a humidity reading up there along with the temp at the same time. Use an online calculator to determine the dew point. Use that dew point and your inside house temp to calculate what the humidity reading for the air coming down from the attic.
Temperature, Dewpoint, and Relative Humidity Calculator
Today I get about 80% humidity outside, 80% in the attic, 65-70% on the first floor directly in line with a vent, and about the same on the second floor. Temp in the house is 75F so dewpoint is about 63. Temp in the attic is 87F so dewpoint there is about 80. I'm not sure these last numbers are right - not sure my hygrometer is giving relative humidity. It just says "humidity".
 
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Old 10-07-17, 02:55 PM
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You are correct that we are looking for what changed from a working system. So far we know there has been moisture added to the attic and your readings seem to confirm that the air in the attic has more moisture than the air outside. I'm assuming the attic temp is higher than outside temp with same RH. Did you dig down to the drywall to see if there is a plastic vapor barrier with a pool of water on top, just guessing.

Did you switch your ac to a continuous fan? This can re-introduce moisture that was left on the exchange unit.

Was any work done?

Bud
 
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Old 10-08-17, 01:52 AM
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So far we know there has been moisture added to the attic and your readings seem to confirm that the air in the attic has more moisture than the air outside.
Reading it over, I said humidity is the same in the attic and outside (80%). I guess you're making an assumption about temperature and working from there for dewpoint? I'll recheck tomorrow with a new hygrometer as I have some doubts about the one I have anyway.

No changes in fan.

I'm going to remove the insulation and replace it tomorrow so I should have a better idea then about any pooled water.
 
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Old 10-08-17, 07:08 AM
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In order to compare simple RH numbers they have to be at the same temperature as temp changes the capacity of air to hold moisture. I am assuming the attic is hotter than outside therefore the 80% reading represents more moisture.

Bud
 
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Old 10-08-17, 10:40 AM
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Today, 10:08 AM #17 (permalink)
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In order to compare simple RH numbers they have to be at the same temperature as temp changes the capacity of air to hold moisture.

Not sure what you mean, I thought relative humidity corrects it relative to temperature.

Anyway the latest highly scientific experimental results are in. I'm assuming the hygrometer is giving me relative humidity because the readout says percent; after some Googling I'm still not sure:

Outdoor: (relative?) humidity 54%; temp 95F; dewpoint 76
Attic: (relative?) humidity 55%; temp 100F; dewpoint 81
House: (relative?) humidity 64%; temp 73F; dewpoint 60

That looks like a difference although I'm not sure what a significant difference would be. There's obviously some error in these cheap instruments.

It's dry outside today, so maybe the attic is also starting to dry out. Removing the damp insulation as we speak.
 

Last edited by suobs; 10-08-17 at 11:35 AM.
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Old 10-08-17, 05:32 PM
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I took out about 8" of insulation that had a sort of small hole from drippage. I'll have to fill in tomorrow, didn't have any 24" ceiling insulation around. I wouldn't say it was wet - more like damp around the hole. There was some minor pooling in the backing below and about a 6" diameter wet spot on a framing member. Some problems with drywall below that but nothing major.

To go back to my original question, should I have the AC guy some out or do you think we have identified the source of the problem?

Does anyone think it could be an AC mechanical problem? I didn't see any holes in the ductwork.
 
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Old 10-09-17, 04:32 PM
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The AC guy says he thinks (it's a two-stage unit) that one stage may be down. Any thoughts on that?
 
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Old 10-10-17, 07:51 AM
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Sorry didn't reply yesterday, had to run to make eye doctor appointment, then eyes were dilated so the computer was a challenge.

Anyway, to summarize without going back and reading everything I don't see the amount of water that leaked into the attic as being a significant contributor. To increase the RH reading that much would take many gallons. The most likely cause was the time frame with power off and no ac. The house would have absorbed a lot of moisture from the air and is now slowly drying out. Keep taking readings and give it a week or two more.

As for the ac unit, I'm not an ac pro, but nothing changed and it is still cooling. An ac unit that is too big may not run for long enough periods to dehumidify as well as it should. If your unit is cycling on for short runs and cooling quickly on a very hot day it is probably a bit too big but once the house dries out it will be fine.

I don't like the excuse the tech gave you about the second stage not working, sounds like BS.

Here is the start of the doc I quickly saved before I left yesterday.
" Not sure what you mean, I thought relative humidity corrects it relative to temperature.

No, here is a definition "the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature." (reference many sources)

So, when air is heated or cooled its RH changes. The dew point is more of a constant number. Temp and RH can see-saw but the dew point remains the same."

Bud
 
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Old 10-10-17, 04:47 PM
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I don't like the excuse the tech gave you about the second stage not working, sounds like BS.
Thanks for the reply. I tend to agree. On the other hand, they may not remember until I remind them but the contract says there's a 1-year satisfaction guarantee, all parts/all labor. So I might just have them check it out before the year is up.
 
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