Indoor humidity, A/C, and exterior paint

[Hank]

In an archived post, I read that indoor humidity can affect exterior paint. I live in central Texas where it's very hot and humid and I have central A/C in my 16 year old house.

I turn off the A/C during the day when I'm at work as per recommendation by the local utility. This way they say I will save $ by having the A/C run continuously for a long period in the late afternoon to cool for evening rather than keeping the A/C on (even if turning it up a few degrees) and it turning on and off during the day.

The concern I have is: my house gets up to 91-94 degrees by late afternoon before the A/C turns on and ultimately cools it to 82-83. I'm concerned that these high temperatures will absorb humidity somehow.

1) Will this create extra humidity that may affect my exterior paint?

2) Could the constant (4-5 months out of the year) fluctuation of 92 to 82 degrees also cause problems to other aspects of the house?

Thanks in advance, Hank

[mark Ransley]

no and no

[CBHvac]

Thats been proven time and time again to be wrong. You set the stat, and forget about it.

Its only cooling to 82F? That is a sign of other problems that are effecting your bill... and it will not absorb humidity...while true that warm air holds more moisture than cool, the humidity levels in your home will not rise much more than what is outdoors, unless you have a water issue.

Again...extra?

Yup.. I have lived in a warmer climate than yours, where the temps regularly break

100F about mid Feb, and stay there till November. Nothing like servicing a unit that someone kept playing with the thermostat and finally tripped the compressor, or warpage of items in the home, to be blamed on the AC...Now...I still have a problem with that 82F final you posted...is that where you have the stat set at? or is that all your unit will do? I kept mine at 74F in the deserts of CA and even with it over 120F outside, it was running like it was supposed to.

[CBHvac]

Ok..just making sure. We get alot of those kind of questions and such this time of year...

Wont hurt the AC unit..it could care less if its 130 or 80 outside...or inside. However, that said, when you have a high indoor temp, and you turn it on, the compressor head pressures are higher, thus, drawing more amperage to run, and increasing wear on the compressor. Unless you have a water issue, the humidity in your home will not increase dramatically while its off...a few points, perhaps. Tons..no. Got lots of air infiltration, then it will be the same inside as out.

Your best bet, to keep the bills low, are to set it, and forget it. Its cheaper to MAINTAIN a temp, particularly a higher temp as you have it set at, than to allow it to try to run for a while trying to bring it down.

Try it for a month and see..

[Hank]

Thanks all, for the helpful replies. I wasn't aware of high compressor head pressures as described. Also, as suggested, probably the best way to know what is most efficient is to give a steady temp a try and compare. Hank

[Darrell]

====== The big "humidity factor" is your climate. If it is a high humidity climate air infiltration will raise the indoor humidity to near the same level.

How long it takes it to do that depends on your home's air infiltration rate and whether it is windy or clam.

The steady temp trial will depend on a proper sized A/C or it might do a lot of short cycling costing you a ton.

The cut-in cut-out differential on all room thermostats ought to be programmable so you could set them for long run cycles even if it meant

5 or more degrees of temp variation.

Sizing the A/C so you get real long run times is essential to control humidity, also it takes 5 to 7 minutes or so for an air conditioner to reach its cooling capacity after a normal shut-down period. Short cycles will cost you plenty of money and never control humidity!

Read my sig' page below on controlling humidity.

[Darrell]

The big "humidity factor" is the climate. If it is a high humidity climate the air infiltration rate will raise the indoor humidity to near the same level.

How long it takes it to do that depends on your home's air infiltration rate and whether it is windy or clam.

The steady temp trial will depend on a proper sized A/C or it might do a lot of short cycling costing you a ton.

The cut-in cut-out differential on all room thermostats ought to be programmable so you could set them for long run cycles even if it meant

5 or more degrees of temp variation.

Sizing the A/C so you get real long run times is essential to control humidity, also it takes 5 to 7 minutes or so for an air conditioner to reach its cooling capacity after a normal shut-down period. Short cycles will cost you plenty of money and never control humidity!

Read my sig' page below on controlling humidity.