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Old 10-26-2008, 10:58 AM   #1
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Humidity with A/C


Does anyone know the approx. max % of humidity that should be present in a home if the A/C is working properly and has been on for two days. Cycling properly. I would think this should be a very low number.
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Old 10-26-2008, 11:47 AM   #2
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Humidity with A/C


Assuming the ducts and unit is properly sized, around 40% at a temp of 75%

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Old 10-26-2008, 11:48 AM   #3
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Humidity with A/C


I believe the "comfort zone" for RH is between 40-60% for those months when you use your AC.

This is from my Aprilaire Humidifier Manual
Outside Temp | Recommended RH
+40F | 45%
+30F | 40%
+20F | 35%
+10F | 30%
+0F | 25%
-10F | 20%
-20F | 15%
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Old 10-26-2008, 11:56 AM   #4
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Humidity with A/C


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Originally Posted by Winchester View Post
I believe the "comfort zone" for RH is between 40-60% for those months when you use your AC.

This is from my
AprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAshraeAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireApril aireAprilaireAprilaireAprilaireAprilaireAprilaireA prilaireAprilaireAprilaireAprilaireAprilaireAprila ireAprilaireAprilaireAprilaireAprilaireAprilaireAp rilaireAprilaireAprilaireAprilaireAprilaireAprilai reAprilaireAprilaire
Humidifier Manual

Outside Temp | Recommended RH
+40F | 45%
+30F | 40%
+20F | 35%
+10F | 30%
+0F | 25%
-10F | 2
Ashrae

0F | 15%






Winchester that is a chart for winter humidification. The OP is asking about summer cooling.

The numbers I posted are the inside design temps that an a/c should maintain according to ASHRAE standard and ARI.
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Old 10-26-2008, 11:58 AM   #5
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Humidity with A/C


LOL you get a cramp in your finger?
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Old 10-26-2008, 08:17 PM   #6
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Humidity with A/C


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Originally Posted by hvaclover View Post
Winchester that is a chart for winter humidification. The OP is asking about summer cooling.
You don't think I'm aware of that? You mean you don't see temps in the negative zone and run the ac?

Give me a break....I supplied what I've read on the comfort zone (40-60 RH summer) and then gave winter RH as because that's the season most of us are seeing here in the U.S. I was just trying to be informative to RH for the whole year. After all, if the question is what RH should be with the AC who's to say he/she knows what it should be in the winter?

I haven't been around here long but I have certainly noticed how you (hvaclover) like to jump on people's posts. Ease up some, if we're reading the posts we're either interested in the answer or just trying to help.
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Old 10-26-2008, 11:27 PM   #7
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Humidity with A/C


I am only answering the question that is asked. And this was concerning summer RH not winter humidification.


In summer ac we are DE-humidifying air in summer, removing moisture, not adding it.

Your chart is only accurate for the winter months.

When an a/c is sized it is done so to maintain the DESIGN TEMP AND RH, for indoor conditions which is 75*f @ 40 to 45% RH.

And as far a jumping on posts, if I can expand or correct an inaccuracy I will.

After all it is my job to do that. But you are welcome to your own perceptions.

I just want to help where I can, like we all do.
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Old 10-27-2008, 08:36 AM   #8
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Humidity with A/C


Depends on the outdoor temps and humidity.
Along with how much infiltration your house has.
And how closely sized your A/C is.

I would say 55%RH is an upper limit, and that would be for milder temp days, that the humidity is high.
45% is a lower limit.

I use 45 as a lower limit. Only because in order to go any lower. Your A/C has to run the blower very slow(or the stat set very low), and loses efficiency trying to remove more mooisture when the humidity is that low.

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