Re: high humidity levels inside house

[Guest guest]

This is strange..have you had a lot of rain this year? Even rain

should not affect the humidity much in a controled enviroment.

Something does seem wrong.

--- In , " mccallalton " <mccallalton@...>

wrote:

>

> does anyone know why my indoor humidity is highe than outside even

> with ac running full blast??? we have replaced the systems within

the

> year and i have had service person after service person out. the

> temperature outside have been hghs of 103 and lows of arpnd 80. at

> the top of the heat, the outdoor humidity is around 20 per cent and

> indoor goes up to 70 per cent. something is wrong.

>

[Guest guest]

mccallalton,

There may not be anything wrong with your a/c even though the

humidity inside is higher than outside with your a/c running full

blast. Humidity can be difficult to understand because the most

common way of measuring it (relative humidity, or RH) is the one that

causes the most confusion.

We tend to think of relative humidity (RH) as the amount of moisture

in the air. The more moisture the more humid, right? But RH isn't

just the amount of moisture, it is actually a comparison (by

percentage) of the amount of moisture in the air to the temperature

of the air. That's why it is called " relative " because the number is

relative to the temperature; it changes with the temperature. You can

have the same amount of water but a different RH at a different

temperature. Likewise, you can have the same RH but the amount of

water vapor will be different at different temperatures.

Because...

Hot air can hold more water than cold air. As the temperature goes up

the percentage goes down. Likewise, as the air gets cooler it can

hold less water so the percentage goes up. In fact, if you cool the

air enough, the percentage will increase to 100%, which means it

can't hold any more moisture - this is when it begins to rain. The

temperature where this happens is called the dew point. Increase the

temperature back above the dew point and it will stop raining because

the warmer air can now hold the amount of water vapor that is in the

air.

The actual amount of water vapor in the air at any given time is

called the Specific Humidity, because it doesn't change. It isn't

" relative. " Relative Humidity does change because it is actually the

comparison of Specific Humidity (amount) to the temperature. Which

means the only way to directly compare the RH in two locations is if

both are at the same temperature.

Which brings us to your house. The temperature outdoors and indoors

is not the same, so we can't simply compare the RH of each.

In fact, 20% RH at 103 degrees calculates to 70% RH at 64 degrees, a

reasonable temperature for your a/c.

Because a/c cools the air at the coils to below the dew point, some

of the moisture will be removed. Without getting into another

description that is even more complex, just understand that the 103

degree air can start with an RH higher than 20%, have some moisture

removed by the a/c, and you are still at 70% RH inside.

On Aug 15 <barb123> posted some excellent information including an

article written by Dave Dombek at accuweather.com. (reprinted below).

Carl Grimes

Healthy Habitats LLC

--------accuweather----------

Dew point is simply the saturation point of the air, or the

temperature to which the air has to be cooled in order to get

condensation. It is really a true measure of how much water vapor is

in the air...the higher the dew point, the more water there is in

the air, and the lower the dew point, the drier the air mass is. In

the summer, dew point is an excellent tool to use in determining how

comfortable, or uncomfortable, it feels outside. Here is a general

summertime guideline for dew points...

Below 50: very dry

50-59: comfortable

60-64: moderately humid

65-69: humid

70-79: oppressive

80 and above: steam bath!

Now you may be wondering...how does dew point relate to relative

humidity? Well, the relative humidity is dependent on the

temperature and the dew point. The closer together the dew point and

temperature are, the higher the relative humidity is. The farther

apart they are, the lower the relative humidity is. Here's an

example of what I mean, and also an illustration why the term

relative humidity does tell you anything about how comfortable or

uncomfortable it is outside.

Let's say we've got a very humid air mass in place, and the dew

point is 70. It's daybreak, and it's very murky outside...hazy, and

perhaps even foggy. The grass, car tops, etc. are all covered with

heavy dew. Let's say the temperature at that time is 70 degrees.

With a temperature of 70, and a dew point of 70, the air is

saturated, and the RELATIVE HUMIDITY at that time is 100%.

The sun comes up, burns off the fog and evaporates the dew. There is

no front coming through that day...no air mass change whatsoever. So,

the air mass will have basically the same amount of water vapor in

it all day long, i.e., the dew point will stay close to 70. Now with

the sun out, the air heats up, and the temperature rises. Let's say

the high temperature that day, around 4pm, is 90 degrees. At that

time, the hottest part of the day, the RELATIVE HUMIDITY is only

50%!!! That doesn't tell the average person anything about how it

feels outside!!!

The dew point is a good tool to use all year long. In the winter

time, the lower the dew point, the drier the air mass is, and the

more likely precipitation will fall as snow, even if the temperature

initially is above freezing. That's because the air temperature will

cool as the precipitation initially evaporates.

The heat index is simply a combination of temperature and dew point,

and how it feels. When the dew point is relatively low...say in the

low 60s or lower, then the heat index is basically the temperature.

However, as it gets more humid (higher dew point), then it feels

hotter than the actual temperature. There really is something to the

expression... " it's not the heat but the humidity " . When the

temperature is quite hot, and the dew points are very high, the heat

index is extremely high. Sometimes the heat index can go into the

dangerous category of 110 degrees or more.

The Real Feel Temperature is something we developed in-house here at

AccuWeather. It takes into consideration other factors besides just

temperature and dew point. It factors in the time of day, the sun

angle, and amount of cloud cover, the winds or lack thereof, etc.

For example, a temperature of 90 and a dew point of 70 will feel

worse at noon or 1 pm with the sun high in the sky than it will at 5

pm or 9 am. Also, a temperature of 90 and a dew point of 70 will

feel worse when it is dead calm than if there is a 15 mph wind

blowing. The same thing goes for 90/70 with bright sunshine vs. 50%

cloud cover. For all of these examples, the heat index will be

identical...no difference whatsoever, since it is based solely on

temperature and dew point. The Real Feel Temperature, however, will

be different for each case.

I hope I answered your question. If so, please close out the

question and give me a rating. Thanks!

Sincerely,

Dave Dombek

Expert Senior Meteorologist

AccuWeather.com

-------------------------------end accuweather----------------

> does anyone know why my indoor humidity is highe than outside even

> with ac running full blast??? we have replaced the systems within the

> year and i have had service person after service person out. the

> temperature outside have been hghs of 103 and lows of arpnd 80. at

> the top of the heat, the outdoor humidity is around 20 per cent and

> indoor goes up to 70 per cent. something is wrong.

[Guest guest]

It is doubtful your absolute indoor humidity is higher than outside, but

your relative humidity may be. As air cools, its ability to hold water

decreases, thus 20% relative humidity at 103 degF may be 50-60% at your

indoor temperature. Check whether RH reads lower if the AC is set to a

higher temperature. Another possibility is that your AC is oversized for

your house, leading to poorer dehumidification.

First check the accuracy of your humidity gauge. If it is correct, you

need to look for other causes. The AC drain line might be clogged, or the

drain pan might not be placed properly, keeping water in the drain pan,

reducing dehumidification. Also, moisture might be added to the house by

some means: a lot of showers, cooking, improperly vented dryer, water line

or sewer leak, or even ground water penetration from a spring.

high humidity levels inside house

Posted by: " mccallalton " mccallalton@...

Date: Sat Aug 26, 2006 4:02 pm (PDT)

does anyone know why my indoor humidity is higher than outside even

with ac running full blast??? We have replaced the systems within the

year and I have had service person after service person out. the

temperature outside have been hghs of 103 and lows of arpnd 80. at

the top of the heat, the outdoor humidity is around 20 per cent and

indoor goes up to 70 per cent. something is wrong.

[Guest guest]

there is something wrong with something because the den area does not cool

right.

" Carl E. Grimes " <grimes@...> wrote: mccallalton,

There may not be anything wrong with your a/c even though the

humidity inside is higher than outside with your a/c running full

blast. Humidity can be difficult to understand because the most

common way of measuring it (relative humidity, or RH) is the one that

causes the most confusion.

We tend to think of relative humidity (RH) as the amount of moisture

in the air. The more moisture the more humid, right? But RH isn't

just the amount of moisture, it is actually a comparison (by

percentage) of the amount of moisture in the air to the temperature

of the air. That's why it is called " relative " because the number is

relative to the temperature; it changes with the temperature. You can

have the same amount of water but a different RH at a different

temperature. Likewise, you can have the same RH but the amount of

water vapor will be different at different temperatures.

Because...

Hot air can hold more water than cold air. As the temperature goes up

the percentage goes down. Likewise, as the air gets cooler it can

hold less water so the percentage goes up. In fact, if you cool the

air enough, the percentage will increase to 100%, which means it

can't hold any more moisture - this is when it begins to rain. The

temperature where this happens is called the dew point. Increase the

temperature back above the dew point and it will stop raining because

the warmer air can now hold the amount of water vapor that is in the

air.

The actual amount of water vapor in the air at any given time is

called the Specific Humidity, because it doesn't change. It isn't

" relative. " Relative Humidity does change because it is actually the

comparison of Specific Humidity (amount) to the temperature. Which

means the only way to directly compare the RH in two locations is if

both are at the same temperature.

Which brings us to your house. The temperature outdoors and indoors

is not the same, so we can't simply compare the RH of each.

In fact, 20% RH at 103 degrees calculates to 70% RH at 64 degrees, a

reasonable temperature for your a/c.

Because a/c cools the air at the coils to below the dew point, some

of the moisture will be removed. Without getting into another

description that is even more complex, just understand that the 103

degree air can start with an RH higher than 20%, have some moisture

removed by the a/c, and you are still at 70% RH inside.

On Aug 15 <barb123> posted some excellent information including an

article written by Dave Dombek at accuweather.com. (reprinted below).

Carl Grimes

Healthy Habitats LLC

--------accuweather----------

Dew point is simply the saturation point of the air, or the

temperature to which the air has to be cooled in order to get

condensation. It is really a true measure of how much water vapor is

in the air...the higher the dew point, the more water there is in

the air, and the lower the dew point, the drier the air mass is. In

the summer, dew point is an excellent tool to use in determining how

comfortable, or uncomfortable, it feels outside. Here is a general

summertime guideline for dew points...

Below 50: very dry

50-59: comfortable

60-64: moderately humid

65-69: humid

70-79: oppressive

80 and above: steam bath!

Now you may be wondering...how does dew point relate to relative

humidity? Well, the relative humidity is dependent on the

temperature and the dew point. The closer together the dew point and

temperature are, the higher the relative humidity is. The farther

apart they are, the lower the relative humidity is. Here's an

example of what I mean, and also an illustration why the term

relative humidity does tell you anything about how comfortable or

uncomfortable it is outside.

Let's say we've got a very humid air mass in place, and the dew

point is 70. It's daybreak, and it's very murky outside...hazy, and

perhaps even foggy. The grass, car tops, etc. are all covered with

heavy dew. Let's say the temperature at that time is 70 degrees.

With a temperature of 70, and a dew point of 70, the air is

saturated, and the RELATIVE HUMIDITY at that time is 100%.

The sun comes up, burns off the fog and evaporates the dew. There is

no front coming through that day...no air mass change whatsoever. So,

the air mass will have basically the same amount of water vapor in

it all day long, i.e., the dew point will stay close to 70. Now with

the sun out, the air heats up, and the temperature rises. Let's say

the high temperature that day, around 4pm, is 90 degrees. At that

time, the hottest part of the day, the RELATIVE HUMIDITY is only

50%!!! That doesn't tell the average person anything about how it

feels outside!!!

The dew point is a good tool to use all year long. In the winter

time, the lower the dew point, the drier the air mass is, and the

more likely precipitation will fall as snow, even if the temperature

initially is above freezing. That's because the air temperature will

cool as the precipitation initially evaporates.

The heat index is simply a combination of temperature and dew point,

and how it feels. When the dew point is relatively low...say in the

low 60s or lower, then the heat index is basically the temperature.

However, as it gets more humid (higher dew point), then it feels

hotter than the actual temperature. There really is something to the

expression... " it's not the heat but the humidity " . When the

temperature is quite hot, and the dew points are very high, the heat

index is extremely high. Sometimes the heat index can go into the

dangerous category of 110 degrees or more.

The Real Feel Temperature is something we developed in-house here at

AccuWeather. It takes into consideration other factors besides just

temperature and dew point. It factors in the time of day, the sun

angle, and amount of cloud cover, the winds or lack thereof, etc.

For example, a temperature of 90 and a dew point of 70 will feel

worse at noon or 1 pm with the sun high in the sky than it will at 5

pm or 9 am. Also, a temperature of 90 and a dew point of 70 will

feel worse when it is dead calm than if there is a 15 mph wind

blowing. The same thing goes for 90/70 with bright sunshine vs. 50%

cloud cover. For all of these examples, the heat index will be

identical...no difference whatsoever, since it is based solely on

temperature and dew point. The Real Feel Temperature, however, will

be different for each case.

I hope I answered your question. If so, please close out the

question and give me a rating. Thanks!

Sincerely,

Dave Dombek

Expert Senior Meteorologist

AccuWeather.com

-------------------------------end accuweather----------------

> does anyone know why my indoor humidity is highe than outside even

> with ac running full blast??? we have replaced the systems within the

> year and i have had service person after service person out. the

> temperature outside have been hghs of 103 and lows of arpnd 80. at

> the top of the heat, the outdoor humidity is around 20 per cent and

> indoor goes up to 70 per cent. something is wrong.

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