Indoor humidity above 70%

[kschwi]

This morning we received an email indicating that our indoor humidity was 76%. Since we are away this month we had our AC set 79. We lowered it to 77 and the humidity fell to 71%. Does that sound too high? Is there something wrong or can this happen from time to time?

[retiredguy123]

It's too high. My thermostat is always set on 78 degrees, and my indoor humidity rarely exceeds 55 percent. Today, it is 44 percent, and it has ranged from 41 to 45 percent during the past 24 hours. And, I don't use any humidity control. I would have it checked by an HVAC company, but you may want to remeasure the humidity with another measuring device first. Is there a window or door opened, or do you have a broken window? Do you have a leak in the house with standing water? Those are some things that could cause high humidity.

[tophcfa]

Definitely too high and a real mold risk. We keep our A/C at 81 when not there and our humidity rarely exceeds 60%, and if it does it’s only by 1-2%. It’s a good idea to keep a dehumidifier in the home as a cheap insurance policy. We keep one on the kitchen counter during the humid summer months so it can drain into the sink and set it to only run when the relative humidity reaches 60%. Prolonged humidity above 70% needs to be addressed ASAP.

[retiredguy123]

Another possibility is that the condensate drain is clogged and the supply air fan is sucking water into the house.

[Pondboy]

You’re mixing up Dew Point vs Humidity.

The long and short of it is that a “dew point” below 60 is what most people think of comfortable. The lower the number, the “drier” the air is. A dew point above 60 means more moisture in the air.

[ton80]

You’re mixing up Dew Point vs Humidity.

The long and short of it is that a “dew point” below 60 is what most people think of comfortable. The lower the number, the “drier” the air is. A dew point above 60 means more moisture in the air.

I think you have it wrong.
A dewpoint of 60F means that moisture forms on surfaces in your home at 60F. This is uncomfortable and has a relative humidity of 100 % which is high mold condition.

A relative humidity of 60 % means that the water content in the air in that house is 60% of the maximum water content that the air at that temperature can hold.

[Topspinmo]

Probably all the recent thunderstorms?

[ton80]

I think you have it wrong.
A dewpoint of 60F means that moisture forms on surfaces in your home at 60F. This is uncomfortable and has a relative humidity of 100 % which is high mold condition.

A relative humidity of 60 % means that the water content in the air in that house is 60% of the maximum water content that the air at that temperature can hold.
After my comment I looked further to find comparisons for dewpoint (F) versus relative humidity (% at T)

Dewpoint considerations are consistent with Pondboy's Post
Dewpoint less than or equal to 55F is dry and comfortable range
Dewpoint of 55 to 65 F is becoming" sticky " range
Dewpoint over 65 is oppressive

To try to link dewpoint and relative humidity I found this comparison which includes the units of measure for typical recommended AC settings
If RH is 50% and indoor T = 80F the dewpoint would be 59 F.

Hope thos helps for comparison without having water contents and graphs.

[Teed_Off]

Check the indoor RH again this afternoon when the air conditioning has cycled on/off several times. We had a foggy morning so it’s highly likely that your A/C did not run at all for several hours and the RH came up during that time.

[villagetinker]

This morning we received an email indicating that our indoor humidity was 76%. Since we are away this month we had our AC set 79. We lowered it to 77 and the humidity fell to 71%. Does that sound too high? Is there something wrong or can this happen from time to time?

Yes I would consider this too high; do you have a trusted neighbor that can inspect your house? I tend to agree with the above comments about the humidity being too high. This could be a malfunction in the AC system, possibly the thermostat. A backup in the drain line typically causes the AC to shut down. If the neighbor can arrange an inspection of the AC system, I would do that also.

[kschwi]

We lowered the temperature and it is down to 67% but that still seems high. We have it looked at on Monday.

[go4fpsb]

We were snowbirds for a couple of years and had a similar experience with too high humidity.. One reason ours was high , I set the fan to run all the time. HVAC guy told me that’s a problem so I reset it to auto and the issue corrected itself. Hope that helps you.

[Rickmartin]

You may want to check your filters inside your home. Also a lot of people don't realize the outside condensing unit coils may need to be cleaned as well. Check condenser drain line to make sure it's free of debris and draining properly.

[Rocksnap]

Another area to check. Is your air handler accessed from the garage? Check the air handler room for any condensation. I’ve seen bad door seals allow moist garage air into this room. Basically it’s like keeping a window open. The AC will never keep up removing all the moisture.

[La lamy]

It is too high, glad you're getting it looked at. A few days above 70% is not a problem, but it can be an issue long term for sure.

[zummy]

Yep, for sure

[daca55]

That is high! You want to try and keep the humidity at 60 or below to prevent damage in your home. I am a snowbird and I bought a thermostat that I can control with my phone from anywhere. I leave it set at 82 and the humidity stays below 60%. I recommend having your system looked at to make sure it’s running ok as the temps and humidity readings don’t sound right.

[Shelbyh]

This morning we received an email indicating that our indoor humidity was 76%. Since we are away this month we had our AC set 79. We lowered it to 77 and the humidity fell to 71%. Does that sound too high? Is there something wrong or can this happen from time to time?

We keep our humidity no higher than 60%.

[ehonour]

I think you have it wrong.
A dewpoint of 60F means that moisture forms on surfaces in your home at 60F. This is uncomfortable and has a relative humidity of 100 % which is high mold condition.

A relative humidity of 60 % means that the water content in the air in that house is 60% of the maximum water content that the air at that temperature can hold.
Ton80 has it mostly right. His definition of dewpoint is correct.

However, a dewpoint number makes no sense at all unless you also know the actual temperature, because what matters is the difference between temperature and dew point. If the difference is zero, as in his example (i.e temp=60 deg and dp=60 deg), then you have water condensing on surfaces. In that condition, the relative humidity is 100%; the air is holding all the water it can possibly hold.

You can have temperature of 105 deg and dewpoint of 80 deg and still feel very dry, with the sweat rapidly evaporating from your skin. (RH of 46%) Or temp of 40 deg and dewpoint of 40 deg and feel oppressively humid. (RH of 100%)

What matters for comfort is relative humidity, not dewpoint.

Concerning the OP question, an indoor RH of over 70% is pretty high. It's not yet mold territory, but something's not right.

[CybrSage]

My thermostat has a max humidity setting, it recommendeds the himidity be set at 65. The AC turns on if it is higher than that.
I have the AC set to 87. I doubt it actually ever gets that high due to needing to reduce humidity.
It is an Ecobee and is wifi enabled.

[MrFlorida]

Way too high, get it looked at.

[gobuck827]

Ton80 has it mostly right. His definition of dewpoint is correct.

However, a dewpoint number makes no sense at all unless you also know the actual temperature, because what matters is the difference between temperature and dew point. If the difference is zero, as in his example (i.e temp=60 deg and dp=60 deg), then you have water condensing on surfaces. In that condition, the relative humidity is 100%; the air is holding all the water it can possibly hold.

You can have temperature of 105 deg and dewpoint of 80 deg and still feel very dry, with the sweat rapidly evaporating from your skin. (RH of 46%) Or temp of 40 deg and dewpoint of 40 deg and feel oppressively humid. (RH of 100%)

What matters for comfort is relative humidity, not dewpoint.

Concerning the OP question, an indoor RH of over 70% is pretty high. It's not yet mold territory, but something's not right.

This is not correct per the National Weather Service, but what would they know? :shrug:

"Dew Point vs. Humidity


The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.

The higher the dew point rises, the greater the amount of moisture in the air. This directly affects how "comfortable" it will feel outside. Many times, relative humidity can be misleading. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. It would feel much more "humid" on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.

So if you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

General comfort levels USING DEW POINT that can be expected during the summer months:

less than or equal to 55: dry and comfortable
between 55 and 65: becoming "sticky" with muggy evenings
greater than or equal to 65: lots of moisture in the air, becoming oppressive"

Dew Point vs Humidity (https://www.weather.gov/arx/why_dewpoint_vs_humidity#:~:text=The%20higher%20th e%20dew%20point,relative%20humidity%20can%20be%20m isleading).

[G.R.I.T.S.]

I would have someone go inside to check it out.

[LeRoySmith]

Ton80 has it mostly right. His definition of dewpoint is correct.

However, a dewpoint number makes no sense at all unless you also know the actual temperature, because what matters is the difference between temperature and dew point. If the difference is zero, as in his example (i.e temp=60 deg and dp=60 deg), then you have water condensing on surfaces. In that condition, the relative humidity is 100%; the air is holding all the water it can possibly hold.

You can have temperature of 105 deg and dewpoint of 80 deg and still feel very dry, with the sweat rapidly evaporating from your skin. (RH of 46%) Or temp of 40 deg and dewpoint of 40 deg and feel oppressively humid. (RH of 100%)

What matters for comfort is relative humidity, not dewpoint.

Concerning the OP question, an indoor RH of over 70% is pretty high. It's not yet mold territory, but something's not right.


I believe you are correct. Most of my education in this area was to keep machines happy but your explanation lines up with everything I learned.

[Topspinmo]

True temperature at location? When I tested Variable thrust jet engines when used wet bulb procedures. Basically we had thermometer that we could wet cloth then spin it close to intake of engine, after minute or two the water evaporates and gives true ambient temperature at that location. On hot dry day this was important to find WOT EPR/PT7 setting based on temperature and barometric pressure. Used those numbers on chart that gave takeoff rated thrust. Based on that setting RPM, EGT, and fuel flow had to be in parameters.

As for humidity in my house runs between 46% to 51%, when A/C kicks in it bring humidity down. Air handler fan speed has lot to do with it also.

[mraines]

This morning we received an email indicating that our indoor humidity was 76%. Since we are away this month we had our AC set 79. We lowered it to 77 and the humidity fell to 71%. Does that sound too high? Is there something wrong or can this happen from time to time?

I generally keep my temp at 79 and my humidity hovers around mid 50's. 71% is way too high. Is your home site built? You might need a dehumidifier.

[Blueblaze]

Instead of leaving the A/C on all the time in our rental, we have a dehumidistat that turns the A/C on only when the humidity exceeds 60%. The A/C is set for 82. We live here, so I check on it regularly in the summer when it's vacant. I have never managed to catch it when it's running, which tells me that the humidity almost never hits 60% indoors. The electric bills agree.

If you leave it on all the time and yours hit 60%, its probably broke, and like others have mentioned, the drain is the most likely culprit.

[LeRoySmith]

wet bulb procedures. Basically we had thermometer that we could wet cloth then spin it close to intake of engine, after minute or two the water evaporates and gives true ambient temperature at that location. .

Those are called Sling Psychrometers. The original kind are pretty expensive (I think in the neighborhood of $150) but you can get cheap digital ones that work pretty well for $25. If you get one spend a little extra and get a psychometric chart (and instructional book). You will learn all you ever care to know about water content of air and how it behaves in concert with temperature.

[Topspinmo]

Those are called Sling Psychrometers. The original kind are pretty expensive (I think in the neighborhood of $150) but you can get cheap digital ones that work pretty well for $25. If you get one spend a little extra and get a psychometric chart (and instructional book). You will learn all you ever care to know about water content of air and how it behaves in concert with temperature.

I couldn’t remember name, thanks.


Those was used on dinosaur jet engine’s mainly P&W J57s TF33s. Been 35 years plus since I ran jet engine on trim pad or test cell.

[Maker]

The humidity reading is too high for normal AC operation. Either the AC is broken (not removing moisture), or some other source is sending excessive water into the interior of the house. Some ideas of things to check...

Verify the temperature and humidity reading with a separate gauge. The Ecobee could be bad. If incorrect, power cycle it and recheck.

Flush the AC drain line. It could be blocked but still flowing a little bit, leaving excessive water to go right back into house. Good PM even if not 100% clogged.

Search for a slightly open window or door allowing outside humid air to get in.

Make sure AC fan is not running constantly.

Make sure all bathroom and stove exhaust fan are off. If running it pulls in outside humid air.

Look for a water leak causing water to be sitting and evaporating. Clothes washer, sinks, toilets, dishwasher, doors, windows, lanai, faucets, AC heat exchanger unit in the garage (or laundry).

Run irrigation zones and look for a geyser shooting water into soffit, forcing water into the attic, then drains onto ceiling. Also look for a head spraying onto windows or walls.

If you have access to a thermal imaging camera, look for issues with wet areas that should be dry.

Make sure toilets and all drains have water in their traps. Beware of a sewer gas smell allowing it, and moisture, easy path into interior.

If you have a thermometer, measure the air temperature from the vents when running. Should be cooling enough to get below the dew point so that moisture condenses (thus lowering the relative humidity). My place controlled to 75 has discharge air at 48 to 52 degrees. RH is 50% to 60%.

Go outside and inspect compressor. Look for all fins to be clean from dirt, fuzz, bugs, insects, pollen. A GENTILE hose spray will wash off lots of gunk. Also away from landscaping blocking air flow. Make sure no plastic bags have been sucked against it. Listen to it start - does the motor zoom right on in less than a second, or are there squeals, multiple start tries, lots of banging, sound like it's struggling to get going, surging, chugging?

Let us know what is found.