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Old 07-19-2020, 10:48 AM   #1
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Still getting duct condensation


Posted before about having our ducts sweating. We had to pull the ceiling off the laundry room for a leak, and that's when we noticed the pipes sweating. Not sure if it started because of the extra moisture from the leak, or was always happening (think we would have noticed), or was just happening from them being exposed.

Turned off AC for a couple of days to dry out and got all the ceiling redone. Thought it would be sealed now, but started AC back up and there's more water. I put the dehumidifier in the electrical closet, which seems to have gotten rid off a lot of the moisture (you can see in the 2nd diagram that the elec closet is open to the ceiling space). But still getting some in the area further from the dehum. especially in the next room over (which would be to the top of diagram 1).

We also had a yearly AC service call a few weeks back, and the tech said the system is running as it should, and shouldnít cause condensation problems. I requested a temp check of the supply and return, and they were good (I set the AC to ~72, the supply was somewhere around that and the return was in the high 50s I think).

I guess this is conditioned space, but it's sort of in between. The crawl space was wrapped in plastic and has a dehum and sump pump, but of course is more humid than the house.

Iíve read about ∆T, relative humidity, static air pressure, dew points, and on and on but donít know what steps to take. Maybe some kind of dehum in the ceiling? Did some quick searches and the ones I found were for basements and crawl spaces, and were probably oversized for what I need, and thus were $$$.

Thanks for the help!
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Old 07-19-2020, 11:55 AM   #2
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Re: Still getting duct condensation


idk, but i get it. all of my ducts are in the unfinished basement. 72d basement and 80d house. and the ducts drip when its hot outside = a/c on more often.
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Old 07-19-2020, 12:21 PM   #3
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Re: Still getting duct condensation


Air dew point temperatures of the several spaces described, including crawl space and duct surface temperatures will be minimum information to avoid anything but guessing about condensation.
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Old 07-19-2020, 02:10 PM   #4
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Re: Still getting duct condensation


Do you have duct sweating or pipe sweating ? They are all caused by lack of (or no) insulation. The large AC line should be insulated from condenser all the way to air handler.
Ducts should also be insulated all the way. hand touch the duct outside, you should not feel cold anywhere. Find out where the condensation is, and check the insulation inside that area.. This is a very common issue, but the theory is very simple, If keep it warm (not cold), you won't get condensation. Do not try to dehum the area, that is not the way to handle this problem.
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Old 07-19-2020, 05:18 PM   #5
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Re: Still getting duct condensation


First off, it's definitely the ducts. None of them are insulated. When I repairing the ceiling, I considered it, but they way they were up in the framing, along with electrical and plumbing, etc. seemed like I wouldn't be able to get them wrapped properly. I was worried if I just did parts I might end up making things worse or getting soggy insulation or something.

I tried to get some temps. Since the ducts are back in the ceiling, it's hard to get good readings. I put one of our temp monitors up in the ceiling and turned off the dehum to get an accuract reading. After a couple of hours, the living room was 73 deg with 58% hum. The ceiling area just off the elec closet was 70 deg with 71% hum. I have a little probe thermometer, not sure if that's really accurate for this, but I held it up to the outside of a duct and got around 65 deg. Supply plenum temp was around 56 deg and a supply register across the house was 61 deg.

If not using the dehum, what's the best way to fix? I mainly put that in just to stop as much condensation as possible to save the ceiling, and it seems to have worked for now. But I'm sure I need a long term solution.

Thanks!
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Old 07-19-2020, 05:49 PM   #6
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Re: Still getting duct condensation


Solve for dew point by plugging in your temperature and relative humidity numbers then you'll know at what temperature the ducts will sweat.


http://dpcalc.org/
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Old 07-22-2020, 09:59 AM   #7
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Re: Still getting duct condensation


Quote:
Originally Posted by SeniorSitizen View Post
Solve for dew point by plugging in your temperature and relative humidity numbers then you'll know at what temperature the ducts will sweat.


http://dpcalc.org/
Thanks, I played around with some numbers, and I'm guessing that my temps and RH from the ceiling area must be off, or the ducts are colders than the reading I got. Otherwise, the dew point should be around low 60's, which is close to what I found.

Knowing the dew point, what steps do I take? Warm the ducts by adjusting AC temp? Lower the humidity or temps in the ceiling somehow?
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Old 07-22-2020, 11:07 AM   #8
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Re: Still getting duct condensation


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Originally Posted by bcemail View Post
Knowing the dew point, what steps do I take? Warm the ducts by adjusting AC temp? Lower the humidity or temps in the ceiling somehow?
Being insulation can't be considered, either of the 2 options you mentioned should benefit. Try one method then the other and choose which you prefer, OR a combination of the two may be desired.
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