Replies

1. 
   BillHartmann | Dec 03, 2006 03:30am | #1

   " I have the heat (gas furnace) set at 66 F and i leave all blinds / curtains open during the day, closed at night. "

   That is part of the problem.

   The one thing that is constant** is the dewpoint. Raising the tempature will reduce the relative humidity, but the dewpoint will not change.

   But what it does is also to raise the interior surface tempature of the glass, maybe raising it above the dewpoint.

   And closing the blinds still allows air to get to the window, but it is reducing the amount of heat that can get to the glass making it cooler.

   ** the only way to lower dewpoint is to either reduce the amount of moisture that is put into the house, such a only breathing outside <G> or to bring in outside air that is drier.

   "The house was reinsulated 2 years ago, and baffles were added in between every trust to increase air. I also had additional vents cut in the overhang along w/ additional vents added when I put on 3 tab shingles 2 years ago. "

   Those are all good for the attic, but have nothing to do with the moisture level inside the house other than good insulating will cause the seal the air that used to leak into the attic from the house.

   Now for other sources of humidity do you have any unvented gas heaters or fireplaces?

   When you run the bathfans is there a gap under the door so that air can flow in?

   What kind of foundation, slab, crawlspace, basement? Is there any moisture problems there or around the outside of the house?

1. 
   konopam | Dec 03, 2006 05:43am | #2

   why is this part of the problem? -- all sites tell you to open windows w/ sun close at night time

   dewpoint -- please explain how this deal w/ the inside of my house?  I am familiar w this outside

   The only reason that i mentioned my insulation and baffles was to say that I believe the house is breathing correctly -- i have read from many sites that tightly wrapped houses are a problem, I was hoping to find an answer if this was the problem

   Yes i have only a 1/4" of gap on all bathroom doors so i hope that is enogh.

   Foundation is a poured basement roughly 9' feet tall, no problems w/ water in the basement have a sump but is has not run since i have been here

1. 
   hurnik | Dec 03, 2006 06:06am | #3

   You say you have heat, (gas furnace) so I'm ASSUMING you mean it's forced air and not hot water heat?Also, ASSUMING you don't have a central humidifier, there's only a few things I can think of:a) Your outside temps are "really" cold or your outside air is very dry --relative to what's inside the houseb) You have poorly insulated windows (I'm assuming they're double-paned low-e windows with either vinyl or wood--not aluminum?)c) Poor air movementGenerally speaking, if the windows are condensing around the edges (in a double-hung window scenario, the usually spots are the "bottom" portions of each window pane), it's usually a combination of the indoor humidity being too high (to be honest, 50% is a bit high for a house even though it's "good" for humans), low outside temps with low humidity (relative to what's inside the house), not good airflow.I live in New York, and have Anderson 400 series windows. When we get a real cold snap (like in Jan where the temps sometimes dip below zero), those nights usually leave me some condensation on the windows. I have gas forced air, with a central humidifer. I have to turn the humidifer down a little (if I don't have the humidifier at all, we all get nosebleeds). Also, opening the blinds/curtains a little to let the air flow helps keep them condensation free. If you have blinds or heavy curtains, the windows don't get air flow and they will really condense.The warmer the house is, the less condensation I've noticed (could also be due to the furnace running more and thus more hot/dry air flowing). Maybe also try keeping the fan on the furnace running to circulate the air and keep it more "even" temperature?66 in the day and 61 is a bit "cool" (even for me). I've found my windows condense more at night, but I don't know if that's because I turn the heat down, and/or because the blinds/curtains usually get closed all the way.With mini-blinds, just turn them open a crack and pull them up an inch or two from the bottom of the sill and that will help a bit.If your condensation is an oval pattern in the middle of the window, then you have a defective window (at least according to Anderson's website).

1. 
   brownbagg | Dec 03, 2006 07:10am | #4

   if its natural gas then the by product of burning is water

2. 
   BillHartmann | Dec 03, 2006 08:51am | #5

   Dewpoint inside works exactly the same as outside.It is the tempature at which the moisture in the air will start to condense.AT "block" of air will have so much moisture that is evaporated into the air. At that amount of moisture will condense at a certain dew point.Now the total amount of moisture that block of air can contain varies by tempature. The warmer the more moisture. RH is the ratio between the amount that is in the air and maximum amount that it can hold.Heating or cooling (as long as there is no condensation) the air does not change the amount of moisture in the air (thus the dewpoint does not chaing) but the maximum amount of moisture and thus the RH will change.http://mcc.sws.uiuc.edu/resources_links/links_calculators.htmAbout 1/2 way down the page is a temp/dewpoint => RH calculator and a temp/RH => dewpoint calculator.Remember that raising and lower the tempature does not change the dewpoint. Add or removing the dewpoint will change the amount of humidity.I belive you said that you have 66*F and 50%RH that gives you a dewpoint of 46.85. I don't remember what you climate is like, but it will be hard to keep the glass above that.At that dewpoint if you let is cool to 61 at night then dewpoint is still 46.85, but the RH is now 60%.As I said keeping the room warmer will not change the DP, but it will help keep the glass warmer.But at that humidity level it will be hard to stop the condensation if you are in a cold area.If you can reduce the RH to 30% (at 66*F) then the DP is 33.69."Yes i have only a 1/4" of gap on all bathroom doors so i hope that is enogh."IIRC the recommendation is 1". For a week try keeping the door open about 1" while showering and run the fan for 30 minutes instead of 20 and see what the RH is after a week."why is this part of the problem? -- all sites tell you to open windows w/ sun close at night time"Well they are correct afar as heat losses go. But it also allows the glass surface to get colder. Now some types of window coverings will seal around the edges to keep the moist room air away from them (and they do a better job of reducing heat loses).

   Edited 12/3/2006 9:19 am by BillHartmann

1. 
   konopam | Dec 03, 2006 04:17pm | #6

   Thanks for the information, yes I live in Southern Wisconsin and right now it has been below 32F over the past 3 days. Furnace is gas and just to clarify I keep the house 61f while we are sleeping or gone and have it set at 66f. I dont have a central humidifier and really dont think that I need one w/ my currently level of humidityThe reason I posted this was to find ways to reduce the high level in my house so I will keep looking and take some of the information posted above

2. 
   DanH | Dec 03, 2006 04:48pm | #7

   > Dewpoint inside is exactly the same as outside.A little misleading, perhaps. Human activities (showering, cooking, even breathing) add more moisture to the air, so generally (except during AC season) the dewpoint inside is higher than outside."Tight" homes (which this one probably is not) actually need extra measures (generally an air exchanger system) to expell moisture in the winter, though more conventional homes (those built before about 1985) generally need to add moisture, to improve comfort.The OP should first make sure that any humidifier on the furnace is turned down or off (and make sure that the humidistat is in fact working correctly and the humidifier isn't running full time).Well, actually the VERY FIRST thing the OP should do is get a carbon monoxide detector, if he doesn't already have one. And he needs to check the furnace for proper operation, as a conventional open flame gas furnace with a plugged flue can add a lot of moisture to the air without other obvious signs of malfunction. (This problem is significantly less likely with high-efficiency induced draft units, as they have sensors to detect a flue obstruction.)Then the OP should inventory all the possible sources of moisture in the house. As stated, run bathroom vent fans for 10-20 minutes after a shower. (And check that the insulation guys didn't somehow block the vent fans -- they should be expelling the moisture outdoors through the wall or roof, not into the attic.)Also consider the possibility of hidden water leaks. This can most easily happen when heating pipes or water pipes are imbedded in a concrete slab, but roof leaks, et al, are also possible. And of course consider the possibility of a regular "leaky basement" as the source of the moisture.Finally understand that a standard drywalled home is a sponge, and holds large amounts of moisture in the gypsum drywall, in wood, in any interior concrete/stone/brick, etc. Any time the outdoor temperature drops suddenly it will take awhile (2-3 days in an older home, weeks in a brand new one) for the inside humidity level to drop.
   People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck

1. 
   BillHartmann | Dec 03, 2006 05:20pm | #9

   I corrected it. I ment to say that DP works the same inside as outside.He said that he understood DP outside, but didn't realize that you could have DP inside.

2. 
   Matt | Dec 03, 2006 04:56pm | #8

   Identify and eliminate or mitigate indoor moisture sources:

   Bath and kitchen fans should be used every time cooking/bathing takes place and these fans must exhaust the the exterior of the home.

   Is there moisture in the basement/crawl space?  If so, deal with it.

   As mentioned combustion appliances inside the home are a moisture source.  These should be check out.

3. 
   IdahoDon | Dec 03, 2006 11:19pm | #10

   Most of your humidity will come from the ground under the house, bathrooms and the kitchen. 

   As others have said, use bathroom fans.  If you don't have bathroom fans install them, preferably with a timer switch.

   In the kitchen many don't like the noise of the fan so they don't use it while cooking.  If that's the case replace the current fan with a remote fan so it's used more often.

   As for the water coming up from the ground, you may need to add a vapor barrier in the crawl space, if so built, or consider a surface treatment to the bare floor if built with a concrete slab.

   Best of luck

    

   Beer was created so carpenters wouldn't rule the world.