Humidity Levels/ Central AC

[Luca]

What is the appropriate humidity level for a centrally air conditioned house when the system is operating properly, in the South ?

[JJ]

Luca wrote in news:m13s94t803jtvck5jdgflmddu8odtt0c9n@

4ax.com:

When it's dripping water, it's working.

[mm]

The impression I got here is that if your AC is too big, it will cool the house before it can get rid of the humidity.

(This surprises me -- I would have thought it would be the same no matter the size of the AC -- but no one who knows anything has contradicted anyone who said this. I certainly don't know enough to contradict anyone.)

And then you will be left with a cool but still damp house. Now I would think if you already have an AC that is too big for your house, there would be a way to solve this problem,, but I don't remember that being discussed.

So I am going to give my usual type of suggestion. Get a decent** hygrometer and take it with you when you go to friends' homes, or even to work and shopping maybe (unless there is some reason why such places are different) and the homes are comfortable, see what their humidity is, and then measure yours. There must be a pretty broad range of what is comfortable, and if you go to enough friends, you'll learn what is comfortable for you.

**It might not even have to be accurate, since the goal is not to measure things and keep records, but to compare the readings at your friends with your own house. To do that it only has to repsond to humidity and go up when it's higher and down when it's less.

[Luca]

I have no doubt it is working.

If my question is read carefully, the reader will ascertain that I was asking what the appropriate level is, i.e hygrometer reading.

[jmeehan]

I suspect there is a little more to the story than this.

Is there an existing problem? If so what is the problem?

In general, the proper sizing and installation of an A/C unit is critical for comfort and the prevention of mold etc. Having a good tech who is familiar with the local conditions and construction is very important.

What is the story? Why do you have a question? What is the real question?

[Luca]

There is no more to the story. I am just a careful home owner who is new to the South, and it's climate. I want to be sure the humidity level in my villa is not too high. There is no problem as I can see. The HVAC unit is 8 yrs old and serviced regularly. I am getting a consistent reading of 60%, and want to know if this is appropriate.

[hallerb]

=BF=BDWhat is the real

quoted text -

sounds a little high, are you certain your measuring dvice is accurate?

[Art Todesco]

Does sound a bit high. Here in the Chicago area, when my AC unit was way too small (it would run for 10 or 12 hours on a 92 degree day) the humidity was very well controlled at about 30 or 35%. After putting in the next size unit (36K --> 42K BTU), it went up a little, but, of course, ran much less. After adding much insulation and new windows, it went up even more, maybe around 40 - 45%. It still feels ok. I'm especially interested in this thread because, after living in this area all my 60 years, I am building in the western mountains of NC and I am curious what to expect in the south.

[Nate Nagel]

Depends on where he is. I opened some windows last night (because it was a frosty 61 degrees outside when I went to bed) and this AM it was about 75% RH in the kitchen.

nate

[Luca]

I am in the coastal SC area and the outside humidity this time of year is at least 80%.

[CJT]

I don't know the answer, but FWIW I'm in Austin, Texas, and our indoor humidity tends to fluctuate around 45% in the summer, as measured by one of those little Radio Shack meters. I suspect as you move towards the coast (e.g. Houston) that value would rise a bit, and further inland (e.g. Amarillo) it would be lower.

And different houses, local weather and thermostat settings surely will result in some differences, as well.

[amdx]

The answer is your personal comfort. I find if I cool the house to 80* and have the humidity down to 40%, I'm comfortable. If the humidity is 60% I need to have it 74* or 75* to be comfortable. I'm not happy with my air conditioner and it's humidity control. I bought a dehumidifier and run it to bring the humidity down to the 40%. This is not a happy solution because the dehumidifer produces a lot of heat and the room it is in gets very warm. The next post will probably say, "your air conditioner's too big, get a smaller unit". Well it might be or maybe not. I don't think it short cycles, but that is on my list to monitor. The air conditioner is old (between 17 and 35 years). If I buy a new more efficient one it will take many, many years to break, considering the $4,000 to $5000 that it would cost to install. I'll get a new one when I'm forced to. Mike

[Art Todesco]

Mike, As you don't want to replace now, you might try to lower your blower speed. Of course, you have to make sure it doesn't ice up. I have an older AC unit which is too large, due to better windows and insulation. I have lowered the blower speed which takes our more moisture and also makes less noise.

[jmeehan]

quoted text -

Generally 40 - 60% humidity is considered good. Too dry and you can experience problems and mold start just above 60%

Note: tools to measure humidity vary greatly. Some are not very accurate and others are poorly calibrated. Since you are close to that 60% area, I think I would want a second opinion (different kind of meter) check. Remember that as you get close to the design limit of the A/C unit, you will be getting lower humidity and you will get less reduction of humidity when you move either direction.

[amdx]

Hey, thanks for the suggestion, I'll look into that. Mike

[ransley]

Humidistats of the analog type are rarely accurate new, they have to be calibrated, if they can, many cant. Digital are usualy better. To calibrate a analog-dial type wrap it in a moist rag for 30 minutes and set to 95%. Go to a store that has a big display of dial units and you will see them all at different settings, maybe 15% off, each other for name brand Taylors. If you are to humid feeling maybe get a dehumidifier as your AC is likely to large. I tried a lower blower speed but I just use a dehumidifier now. A lower blower speed can freeze your coil.