Humidity levels

[Whiskeymike]

I've seen something interesting with the humidity in my house and hoping you guys can provide some insight.

I'm in Austin, TX, and we are already getting July type heat with the last week avg 90 degrees, up to 98 and the lows have been around 70 at night. The humidity has been pretty high, although Weather.com is saying the current humidity is 59% and the average has been higher lately (60-80%).

Anyways, long story short, I have two ecobee thermostats to run two AC units, one upstairs and one downstairs. In looking at those, it reports the humidity downstairs is 59%, and upstairs is 68%. Both AC's have been running pretty close to non-stop because of the heat and I keep it around 71 degrees.

Shouldn't the humidity inside the house be 20-30% less because the the AC is condensing out water vapor? In the past, I've always seen it quite a bit lower inside than outside. Just not sure what has changed.

FWIW, I don't have a lot of house plants, standing water, aquarium, or other things besides a teenage son and daughter that would contribute to higher humidity.

Also, I had the AC repair guy out last week to service all of the units. He cleared the drains, and did normal maintenance.

 

[Brian_WK]

The lower the air temp the lower the ability to hold water hence higher humidity.

Brian

 

[Trey T]

above 60% RH is high. Does the house feel clammy during the day? Your house should be below 50% RH if your system is running constantly like that 24/7. But geez, 71degF?

Right now my area is 52% RH; my house is 52% RH @ 79degF. When I come home the RH would drop to about 45%RH @ 75degF.

 

[EOC_Jason]

If your AC's are running constantly, they sound undersized for the house (or you have other issues like people leaving a door or window open or poor insulation).

I would assume your A/C guy did a delta-t to make sure they were cooling properly? If not, you can do it yourself with a couple thermometers... If they aren't cooling enough they won't be pulling the the moisture out of the air. Or if they are undersized and your house is heating up faster than they can cool then you are just SOL...

 

[Bretny]

Your breathing, cooking and showering in the house? Your adding humid air. My house is some times more humid inside than out too.

 

[yeldogt]

That does seem odd ... are you seeing any water flowing outside?

Do you have the fan on auto ... if a single speed and set to continuous this can affect humidity.

I had a problem in my house after I did a lot of energy upgrades -- the 4T unit on the first floor was just too big for the new lower load -- so it would short cycle. But -- that's not what is occurring in your house if its running all the time.

I can easily get mine to 50% -- or lower if I allow the system overcool.

 

[bobbyjean]

are the t'stats new, do you have a rh reading from them alone,
are the air handlers located where you have access...if in attic ...check for a secure return connection...especially if it's flex duct
how about bathroom exhaust...everything working there....i find i need to take them apart every few years to clean the "mung" out.

 

[Falcon67]

I'm calling undersized unit(s). We will be running in the 100s starting today and going for maybe next 7~10 days. It rained last night, and we both shower and I water like crazy outside to keep the grass from catching fire LOL. No humidity issues - 3.5 ton heat pump unit, 1660 sq/ft. Lots of house plants. System cycles normally in high temp situations. Yes, our average RH is lower out here than Austin but we still get 50+. could be worse - you could be in Houston.

 

[Fixin'Stuff]

... could be worse - you could be in Houston.

Where the humidity is currently 96%.

My Mr. Cool mini-split for the garage will be delivered in about a week.

 

[930dreamer]

AC temp set at 72 degrees, our house RH stays right at 55%, going to be 100 today but dryer then Austin, TX. Cold and feels dry inside.

 

[Radix2]

You need to be careful comparing humidity at different temps. 50% at 98degrees is a LOT more water than at 71 degrees.

So your system is taking a lot of water out of your inside air.

Does it Actually feel humid ? (you need to be pretty dry at 71 not to be clammy) or are you just comparing the numbers and thinking it is a problem?

 

[Trey T]

I’m at an in-law’s home now and one side of the home is pushed to 72degF at night and it’s clammy as hell. Their issue appears to be overflowing of primary drain pan - I saw the secondary line dripping.

@71degF, he must be having same issue

 

[metlmunchr]

If the space temperature is holding at the setpoint, then humidity control problems are most always related to a too high evaporator temperature or handling too much air across the evaporator.

Either condition causes the same problem which is a too high discharge temperature. The discharge air is saturated (100% RH) at the discharge temp, and while the total moisture in the air remains constant, the RH decreases as the discharge air mixes with the air in the space and warms to the space temperature. The lower the discharge temp, within normal operating limits, the lower the total moisture in the air and the greater the ability of that air to lower the RH in the space.

In non-technical language, you can lower the space temperature with 60* air but you won't be able to hold the RH at the ideal 50% with that air. Assuming there's no significant duct leakage allowing the return to pull in unconditioned air, the first place I'd look is the evaporator temp which indicates a loss of capacity due to a refrigerant leak or some obstruction like a clogged liquid line dryer.

 

[justinjoyal]

If the space temperature is holding at the setpoint, then humidity control problems are most always related to a too high evaporator temperature or handling too much air across the evaporator.

Either condition causes the same problem which is a too high discharge temperature. The discharge air is saturated (100% RH) at the discharge temp, and while the total moisture in the air remains constant, the RH decreases as the discharge air mixes with the air in the space and warms to the space temperature. The lower the discharge temp, within normal operating limits, the lower the total moisture in the air and the greater the ability of that air to lower the RH in the space.

In non-technical language, you can lower the space temperature with 60* air but you won't be able to hold the RH at the ideal 50% with that air. Assuming there's no significant duct leakage allowing the return to pull in unconditioned air, the first place I'd look is the evaporator temp which indicates a loss of capacity due to a refrigerant leak or some obstruction like a clogged liquid line dryer.

Exactly what I was about to say.

I’m not sure why some are mentionning undersized units as by OP’s first post they are running constantly yes, but that would not cause high RH and he mentionned it used to be fine.

Loss of capacity is likely. Did the « repair guy » do anything other than cleaning stuff ? Did he take measurements or something?

 

[Trey T]

My in laws ran the unit constantly, seems like 24/7, like the OP. A tech came out and confirmed my diagnosis, failed primary drain line.

It was 100degF yesterday, and felt like 105degF outside

 

[Whiskeymike]

Sorry, catching up on several questions.

When I said constantly running, I should have been more specific. It's running total, probably 1/2-2/3's of the day which feels pretty constant, but I didn't mean 24/7. I also have the fans run a minimum of 15 minutes when the AC kicks on, just to continue to circulate air. It's an option on the ecobee thermostats, and it seemed like a good idea, but I don't know for sure.

My main concern was that when I looked at outside humidity and inside humidity, I was surprised that there wasn't a bigger difference in humidity between outside/inside. But point taken that humidity is relative to temperature, so it's not apples to apples comparison.

Most of the time, it doesn't not feel clammy, but occasionally it does on especially humid days.

The units are 17 years old, so it may be time to upgrade.

 

[LS6 Tommy]

When was the last time you had the units inspected? Sounds like you might have a capacity loss to me, too.
Tommy