Indoor Humidity Rising

[jm123]

The indoor humidity in my air conditioned home as risen recently. I'm in a very dry climate (outdoor humidity in Southern AZ is about 5% right now) but noticed over the past couple of days the indoor humidity rising. Could this be caused by HVAC condenser/evaporator problems?
Thanks!

[newoldtech]

If your air conditoining is maintaining the proper temperature in your house its probably working fine. The only problem could be if the unit is oversized it might not remove the humidity fast enough. Try lowering your thermostat a little and see if that helps.

[mjk_na]

Originally posted by jm123
(outdoor humidity in Southern AZ is about 5% right now)

Do you need relative humidity lower than that?

http://www.air-conditioner-selection.com/comfort-zone-air-conditioner-sizing.html

[jm123]

The unit is cooling the house fine and not running any longer than it used to. The indoor humidity is a comfortable 35%, but it never used to get that high. I was just wondering if it’s normal for an HVAC system to put that much more moisture into the air.
Thanks!

[plain spoken]

Cooling system have no way to add moisture to the air. They normally remove moisture, but in and of themselves can not add what is not already there. In other words they can not make water. They can distribute moisture from other sources, maybe a shower fan not working, clothes dryer not venting, stopped up drain line etc. If you have a humidifier on your system, sounds like you should, maybe it is stuck on.

[teddy bear]

Adults add .25 lbs./person of moisture per hour. One lb. of water raises the %RH in 1,000 sqft, of space 8%RH. Your outside dewpoint is 27^F. At 75^F inside, 27^F dp = 25%RH. Add a little inside moisture and you will have 35%RH. Appears normal to me. Let me make this clear. A dehumidifier will not help. Now that was not so hard to say. TB

[hetrola]

Do you have your fan on continuously. If so the the moisture from the coil could be blowing back into the house in the off cycle.

[hetrola]

Just at a home the other day similar scenario.
Didn't know what was adding humidity.

A 50 gallon fish tank was the culprit.

[jm123]

Thanks for the replies! We don't run the fan continuously and haven’t recently added any obvious sources of moisture. Another mystery of desert perhaps...

[mjk_na]

Did you change the usage duration of the AC unit?

Do you have a humidifier?

[drk]

35% RH I would not worry about that!!!

[lonnirat]

Originally posted by drk
35% RH I would not worry about that!!!

Ditto.

[beenthere]

When did you have it serviced last.

If the indoor coil is getting dirty, then it may not be removing as moisture as it use to.

[jm123]

I’m not so much worried about the 35% RH as the reason for the increase. It has never been professionally serviced since the initial installation six years ago when the house was new and the only maintenance has been the monthly filter cleanings. Probably time to get the coils cleaned… Thanks!

[kevinmac]

I agree on the dirty coil, it may be keeping water from properly draining off the coils, and not removing what it should. The other thing is make sure the condensate line is free and clear to allow condensation to drain properly.

[teddy bear]

At 35%RH, the coil is not getting wet. 75^F, 35%RH requires a <45^F temp coil temp to get wet. TB