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Old 10-24-2011, 12:48 PM   #1
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How much humidity in house?


I have a new home (1yr) and we are approaching winter here in Fargo. How much humidity should I have in the house?

Right now it's 50% which is pretty comfortable. But once it gets cold out the windows will start to frost over and the like so it's nice to lower the humidity down some to prevent it.

What should my target be given I want my wood cabinets and trim to last etc.

I am using a stand alone dehumidifier currently in the house.

Also does a direct vent natural gas fireplace add humidity or not?

Thanks!

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Old 10-24-2011, 01:07 PM   #2
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How much humidity in house?


This from a humidifier maker's literature. Temps are in degrees F to prevent inside condensation. To make it even easier connect an automatic control to your humidifier that has an outside temp sensor.

Edited for clarity:

Outdoor temp............Max Indoor RH
Deg F....................... to prevent condensation

+40............................45%
+30............................40%
+20............................35%
+10............................30%
0................................25%
-10.............................20%
-20.............................15%

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Last edited by raylo32; 10-24-2011 at 02:37 PM.
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Old 10-24-2011, 01:19 PM   #3
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How much humidity in house?


I wouldn't recommend dropping below 30% if you can help it. Once you get below that you are going to notice very dry on nose and throat, plants will not be happy, house may get more noticably dusty, static electricity build up could be noticable, etc. it may also dry out your wood furnishings as you have previously alluded to.
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Old 10-24-2011, 01:39 PM   #4
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How much humidity in house?


I cant imagine that high humidity in the winter in Fargo would be a problem. I would think that you would have a problem with low humidity in the winter.
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Old 10-24-2011, 05:52 PM   #5
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How much humidity in house?


Ok thanks guys...

Well I think the humidity outside is generally quite low, but it's a new house so there is a ton of moisture in it. Last year I had to wipe the windows down 3x a day, there were literally puddles on all the window sills etc.
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Old 10-24-2011, 06:21 PM   #6
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How much humidity in house?


That's not good because the same thing is likely happening in the walls. What kind of heat do you have?
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Old 10-24-2011, 06:31 PM   #7
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How much humidity in house?


Its forced air natural gas. I don't think its in the walls it's only at the windows plus if was in the walls we would water coming out everywhere.
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Old 10-24-2011, 06:45 PM   #8
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How much humidity in house?


hvac dave makes a great point humidity affects the entire house....walls, floor,furnishings, and so on in the winter months we recomend staying around 35% ....our customers live in pa
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Old 10-24-2011, 07:20 PM   #9
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How much humidity in house?


Are you asking about a direct vent, as in its combustion air is brought in in a pipe directly to it, and its vent goes directly outside?
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Old 10-24-2011, 10:41 PM   #10
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How much humidity in house?


Yes that's the one.
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Old 10-25-2011, 12:16 AM   #11
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How much humidity in house?


Quote:
Originally Posted by live4spd View Post
Ok thanks guys...

Well I think the humidity outside is generally quite low, but it's a new house so there is a ton of moisture in it. Last year I had to wipe the windows down 3x a day, there were literally puddles on all the window sills etc.
The first thing I would be looking at, is that the bathroom vent fans are running like they should, and venting moisture outside. Also checking to make sure that the dryer vent is clean and exhausting properly.

Our house is pretty air tight, from everything that I have done, and we never see moisture problems. The worst enemy in a home, is no fresh air coming into the home, and the bath & dryer exhausts placing too much moisture into the home. You can get a humidity sensing switch for the bathrooms, that will not shut off the exhaust fans, until it reaches the proper humidity level. Also, having dampers on the bath exhaust to close to keep outdoor air from entering helps, same as making sure that the dryer damper is closing as it should.

I use a Radioshack remote sensor thermometer & humidistat, with a sensor in our basement and one in the attic to monitor humidity levels and temperatures. We keep our home around 68 in the Winter, and humidity tends to stay around 45% both in the basement and main floor. When it is warmer, even with the a/c running, it spikes about 65% at the highest, but tends to stay in the low 50's.

So, the key would be to constantly monitor the moisture levels in the home, and if you do not have a humidifier on the hvac, use a room unit and run to put moisture into the home if it drops below 45%. If you have a humidifier on your hvac, get it checked out to make sure it is working properly, and not dumping too much moisture into the home.
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Old 10-25-2011, 05:15 AM   #12
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How much humidity in house?


Quote:
Originally Posted by live4spd View Post
Yes that's the one.

It won't add or remove moisture to the house.
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Old 10-25-2011, 06:30 AM   #13
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How much humidity in house?


If the humidity is high enough inside and the temp is low enough outside you can get condensation in the walls and you would likely not notice it unless/until you pulled some drywall off and found damp or moldy insulation.

Here is a good discussion of in-wall condensation. What you want to avoid is what they show in Fig G. where the wall temp gradient is such that the dewpoint occurs in areas and materials that you don't want to get damp. The factors that determine this are the wall design and the outside temp, of course, that are what they are, and the inside dew point that, that you can influence with a humidifier or other behavior.

Probably they design for this up there with the extreme low temps you get perhaps by using a thicker layer of EPS against the outside wall since this stuff won't be affected. But you still need to think about controlling the inside humidity.

http://www.tlpca.org/images/articles_condensation.pdf
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Old 10-25-2011, 09:00 PM   #14
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How much humidity in house?


interesting article. thanks for the advice guys!
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Old 10-26-2011, 10:28 AM   #15
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How much humidity in house?


A direct vent gas appliance does NOT add humidity to the house. What is does do, is reduce infiltration of outdoor (usually lower humidity) air.

With all conditions inside the house being the same, lower infiltration tends to maintain indoor humidity.

My case in point: before direct vent, static shocks. After direct vent, no shocks.

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Last edited by veesubotee; 10-26-2011 at 10:29 AM. Reason: minor edit
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