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Old 07-01-2014, 07:32 PM   #1
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Condensation on Duct work/ Wont go below 71


Today its been about 90 degrees with about 150% humidity. My wife loves the house cold so its been set inside for 68 degrees, after about 5 hours it will not get anywhere below 71 on the thermostat. I know it will go lower as it always does on less hot days.

We also noticed we have condensation dripping from the pipes in the basement. We have a dehumidifier also running if that makes a difference or not. What can make this better? What can we do? Is their something wrong with our air conditioner? I can feel cold air coming from the registers still.

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Old 07-01-2014, 07:54 PM   #2
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Condensation on Duct work/ Wont go below 71


Your ducts have reached dew point temperature and you can solve the dripping problem by raising the temperature to around 75 and using ceiling fans. I suspect too many people don't understand as the room becomes cooler the higher the relative humidity becomes. As the humidity increases it becomes more uncomfortable so the tendency is to lower the temperature even more etc. etc.

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Old 07-01-2014, 08:36 PM   #3
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Condensation on Duct work/ Wont go below 71


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Originally Posted by Fairview View Post
Your ducts have reached dew point temperature and you can solve the dripping problem by raising the temperature to around 75 and using ceiling fans. I suspect too many people don't understand as the room becomes cooler the higher the relative humidity becomes. As the humidity increases it becomes more uncomfortable so the tendency is to lower the temperature even more etc. etc.
We usually keep it on 68 all summer, just noticed today that its been on 68 but says its 71. Got to looking around and seen all the condensation dripping. Is there anything besides dropping the temperature that can help?
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Old 07-01-2014, 09:07 PM   #4
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Condensation on Duct work/ Wont go below 71


If you insist on 68 degrees there is a few things you can do to stop the dripping.

1) install enough de-humidifiers to lower the dew point temperature below duct temperature which may need to be in the 48 to 50 range.
2) wait for the weather conditions that has a lower dew point temperature.
3) increase the duct insulation.
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Old 07-01-2014, 09:33 PM   #5
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Condensation on Duct work/ Wont go below 71


If your a/c didnt have a problem before keeping it at 68 degrees and now it wont and there is condensation dripping from your duct work, It sounds like your a/c isnt working right and its not removing the moisture from the air in the house. Have it looked at by a good a/c tech if youre not capable of doing it

What is the temperature of the air entering your cold air return, And whats the temperature of the supply air closest to your air handler, And whats the relative humidity inside your home
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Old 07-02-2014, 06:54 AM   #6
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Condensation on Duct work/ Wont go below 71


I would check and make sure that the water is draining well from your air conditioner
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Old 07-02-2014, 09:24 AM   #7
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Condensation on Duct work/ Wont go below 71


Another highly subjective and quick check is to make sure you suction refrigerant line (big one) is cold (beer can cold :-) ).
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Old 07-02-2014, 09:34 AM   #8
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Condensation on Duct work/ Wont go below 71


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Originally Posted by cincinnati guy View Post
We usually keep it on 68 all summer, just noticed today that its been on 68 but says its 71. Got to looking around and seen all the condensation dripping. Is there anything besides dropping the temperature that can help?
Dropping the temperature won't help but it will certainly make matters worse. Refer to reply #2.

And I'm sure glad I'm not paying your electric bill.
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Old 07-02-2014, 09:44 AM   #9
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Condensation on Duct work/ Wont go below 71


And as far as getting the house cooler than 71 degrees, you might have reached the limit of your unit's cooling ability at that outdoor temperature. A/C doesn't have infinite cooling abilities and depending on the particulars of your climate, house and A/C system you might only be able to drop the temp 25 or whatever degrees when it's running full tilt. That same delta on a cooler day would get you to 68 but not yesterday.

If you used to be able to keep the house at 68 on these 90+ days then you may have some issue cropping up that needs looking at.
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Old 07-02-2014, 10:12 AM   #10
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Condensation on Duct work/ Wont go below 71


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And as far as getting the house cooler than 71 degrees, you might have reached the limit of your unit's cooling ability at that outdoor temperature. A/C doesn't have infinite cooling abilities and depending on the particulars of your climate, house and A/C system you might only be able to drop the temp 25 or whatever degrees when it's running full tilt. That same delta on a cooler day would get you to 68 but not yesterday.

If you used to be able to keep the house at 68 on these 90+ days then you may have some issue cropping up that needs looking at.
And a 90 day with an outdoor dew point temperature of say 75 is a whole different ball game for an AC than a day with the outdoor DP temp. of 40 or 50.
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Old 07-02-2014, 10:28 AM   #11
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Condensation on Duct work/ Wont go below 71


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And a 90 day with an outdoor dew point temperature of say 75 is a whole different ball game for an AC than a day with the outdoor DP temp. of 40 or 50.
You mean latent heat matters? ;-)
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Old 07-02-2014, 10:42 AM   #12
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You mean latent heat matters? ;-)
Not only matters but matters a bunch.
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Old 07-02-2014, 02:58 PM   #13
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Condensation on Duct work/ Wont go below 71


Cincinnati design temperature is 12* winter and 90* summer. So your system is doing all it can at 90 plus degrees. You need to insulate the suction line to stop it from dripping.

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Last edited by Bitters; 07-02-2014 at 03:01 PM. Reason: more info
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