humidity highest in room with AC on


  #1  
Old 06-22-10, 06:53 PM
L
Member
Thread Starter
Join Date: Oct 2004
Location: PA
Posts: 2,178
Received 8 Upvotes on 8 Posts
humidity highest in room with AC on

why would a bedroom with a closed door and the AC on only in that room have the highest humidity in the house?
 
  #2  
Old 06-22-10, 07:39 PM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
Room to cold! Unit fan running all the time and putting the rh back in the air! Air leaks around unit!
 
  #3  
Old 06-23-10, 05:41 PM
L
Member
Thread Starter
Join Date: Oct 2004
Location: PA
Posts: 2,178
Received 8 Upvotes on 8 Posts
interesting, the room is about 2-3 degrees colder than the other house space and i had the santa fe running all night in the utility room and the main areas in the house got down to 50% while the bedroom was about 65% with the door closed . of course it still felt better but i just hate mysteries. then again there's the theory i'm full of hot moist air
 
  #4  
Old 06-23-10, 06:46 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,498
Received 66 Upvotes on 61 Posts
Perfectly normal!

Humidity is measured as a relative value.
It is a percentage of moisture compared to how much actual water vapor it can hold.

The warmer the air, the more moisture it can hold.
The actual amount of moisture throughout the house will be fairly even so in the colder room the actual amount of moisture the air can hold will be less so the percentage will be higher.

Make sense?
 
  #5  
Old 06-26-10, 06:59 AM
L
Member
Thread Starter
Join Date: Oct 2004
Location: PA
Posts: 2,178
Received 8 Upvotes on 8 Posts
i'm slowly wrapping my head around it
 
  #6  
Old 06-26-10, 08:09 AM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,498
Received 66 Upvotes on 61 Posts
Humidity levels have a strong affinity for an area with less moisture so levels tend to be fairly even within a home.
Because the relative humidity readings will change with temperature this quality of air will drive people crazy if they obsess over it.

Even the normal swing of temperature within a space will cause the reading to change slightly.
So, if you are trying to establish a humidity level don't worry so much about it.

If you want to dive deeper into it here is the next step:

Click image:

Image courtesy of truetex.com

Grains of moisture/lb of air is where it is at in terms of a humidity measurement.
The chart is not that hard to use.
You line up the relative reading you get and drop down at the current temperature.
The gr/lb can then be read on the right.
If you get accurate temperature and humidity readings you will then find the actual moisture will be consistent within a space.

There are several good sites where this is explained well.
A bonus of this topic is if you understand this you will have a good basis of understanding comfort cooling/heating.
 
  #7  
Old 06-26-10, 11:23 AM
E
Member
Join Date: Feb 2010
Location: usa
Posts: 564
Upvotes: 0
Received 0 Upvotes on 0 Posts
maybe cuz there is no return in that room. returns suck in air and are the only way to remove humidity. if it does not have a return, leave the door open.
 
  #8  
Old 06-28-10, 09:02 AM
L
Member
Thread Starter
Join Date: Oct 2004
Location: PA
Posts: 2,178
Received 8 Upvotes on 8 Posts
- well it's more a curiosity than obsession but with my mold issues, yes it's always being monitored. during my off peak hours I like to run my santa fe to get the humidity below 60 in bedroom /bathroom (which are always higher than other parts of the house for some reason). the funny thing is i always thought the RH comes from under my house but the part with highest RH is over the dry part of the house...the lower RH is over my 'moat'

-i have thru the wall units not central air
 
  #9  
Old 06-28-10, 09:19 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 9,457
Received 47 Upvotes on 43 Posts
The other piece of information we need is the outside temp and humidity RH. Since all homes exchange huge quantities of air, trying to lower the moisture level inside the home to below what is outside is a challenge. Now, the numbers will be confusing as GregH was explaining, but basically, if it is warm and humid outside, it will be cool and even more humid inside, less the moisture the ac is removing. 90 outside at 80% RH with 78 inside at 80% RH is a big improvement, even though the RH is the same. Taking it down to 78 and 60% RH would be a really big improvement.

So, your room to room variations may be related to the outside temp and RH and where the air is leaking in. As a reference, a really tight home will still replace all of its air every 3 hours.

Bud
 

Last edited by Bud9051; 06-28-10 at 09:21 AM. Reason: correction
  #10  
Old 06-28-10, 05:47 PM
L
Member
Thread Starter
Join Date: Oct 2004
Location: PA
Posts: 2,178
Received 8 Upvotes on 8 Posts
ok here's an example... right now my bedroom is 79/63, bathroom is 79/58, outside is 79/77, and the sensor 5 feet from my living room window AC unit thats been running for the past 4 hours is reading 78/48 (for once my bathroom is higher than the bedroom lol)

air leakage in bedroom is the thru the wall AC unit of course

air leakage in the bathroom is a thru the wall exhaust vent

oh and i have the farthest thing from a tight home lol...well 1/2 does have new windows

and i do have to recommend the santa fe compact for anyone needing a unit, when the AC is off, the RH comes down universally through the entire house. It's one powerful unit and does it rather quickly.
 
  #11  
Old 06-28-10, 06:11 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 9,457
Received 47 Upvotes on 43 Posts
Lucky, the air leakage is actually everywhere. Under the walls around the windows, plumbing under the sink, electrical recepticals, and more. When we ron a blower door test and watch with an IR camera, we see all of the leaks big and small.

Since your ac units seem to be reducing the humidity and not the temperature, they are most likely too small for the heat gain in those rooms. If the reverse were happening, the temperature was low, but the humidity was barely changed, then the ac units would be too big.

Since air sealing is easy, inexpensive, and effective, that's where I would start. It would lower your RH, lower your temmperature, and right size your ac and of coures reduce your electric bills. More insulation can help as well.

Here is a good link on the issue of air sealing, slow to open, but good:http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
  #12  
Old 06-29-10, 01:59 AM
S
Member
Join Date: May 2009
Posts: 111
Upvotes: 0
Received 0 Upvotes on 0 Posts
Excellent analysis and recommendation, Bud.
 
  #13  
Old 07-07-10, 05:16 AM
L
Member
Thread Starter
Join Date: Oct 2004
Location: PA
Posts: 2,178
Received 8 Upvotes on 8 Posts
[QUOTE=GregH;1740546]

The warmer the air, the more moisture it can hold.
The actual amount of moisture throughout the house will be fairly even so in the colder room the actual amount of moisture the air can hold will be less so the percentage will be higher.
[QUOTE]

well with it being 100 out i sure got a good example of your description last night. With bedroom door closed and the wall unit on, the temp was 75 this morning and 65% RH but the 80 degree unconditioned bathroom next door was in the 50s RH. Thankfully this has been a dry heat.

Re: the blower test i did have one done 2 years ago and followed him around checking things out. 1/2 house has new windows but what was letting in tons of air were 'broken' seals under the windows and around door frames. I pulled all the windows apart and was amazed to find that there was just an open cavity there. So i used the foam in the blue can, love that stuff, and now they are all sealed up well. Also i began putting outlet insulators all over the house because the test showed a lot coming through there.

I also bought, just for the fun of it, an infrared gun thermometer. I wanted to see how cold the hardwood was compared to a carpeted section and it's 1-2 degrees cooler without the carpet. Clearly it's in insulator against my crawlspace. The gun is also useful for wall temps interior vs exterior but i havent insulated the walls or anything yet. I really want to do the attic this year once it's fall since there's only r11 in spots.

while we are talking humidity, can mold grow in high humidity even in swealtering summer temps? i'm very aware of all this RH because i have a severe mold issue in cabinets etc and just was wondering if it's worth running the santa fe in summer or the heat will keep the mold at bay even in 80% RH
 
  #14  
Old 07-07-10, 08:20 AM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
Rh over 55% will support mold growth. Best to run ac or dehumidifiers to keep rh below 55%
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: