Freaking out - window condensation

[duncanshannon]

hi-

i've been working on my house this summer (new siding, new windows).  My windows are getting pretty wet from condensation and i'm starting to kinda freak out. It started as soon as it got 20's/30's.  Now that its in the single digits, the condensation is starting too pool up on the window sashes (which i havent finished yet...)

How in the world do I get that to stop / happen less?

Some probably relevant points:

1) whole house has had new siding applied, including tyvek.  It did not have house wrap before.  (build rite sheating). 
2) whole house has new windows - high quality, qualified for tax rebate levels of efficiency.
3) condensation is the worst in the master bed/bath - not a big surprise i guess.  We have a timer on the fan and it runs for 60 minutes (so prob. 50 mintes past the end of the showers) every day.
4) I still have some walls w/o insulation / vapor barrier and sheetrock.  Master bedroom only has about 1 16" wide (8' high) section that needs insulation and vapor barrier.  There is a 10' area that has VB on, but no sheet rock.
5) high efficiency furnace.  Says humidity is within 5% of target (which changes based on outside temp).

With the change in temp from 20's to 10's/single digits, i've noticed more condensation on the windows in the rest of the house.

its obvious that its the worst in the bed/bath area. thats to be expected right?

it seems reasonable that the lack of finishing the interior wall could be a factor. is it much of one?

Email into the HVAC guy... to see what else I should be doing from his pov.

my major concern... could it be an indication that i screwed something up on the window installs?  They all have the window flashing tape (top and two sides) over the nailing fins and I have Great Stuff filling the void between the 2x6 and the window (where practical... some a couple areas got pretty tight, so not sure how much made it in).

ive got a new indoor temp/humidity guage for the bedroom en route (thanks amazon prime). 

its a pretty heavily discussed topic on the internet... not a ton on how to remediate it.

thanks...

thanks...

[Squirl]

I'm no expert, I would wait for others to weigh in in addition to my comments.

It sounds like you did something right on the window install.

Condensation is humid air hitting the ice cold glass.  Just like a glass of ice on a hot day.  If your windows were leaking air the water vapor would go right out the window or any other crack or crevice, and the air around the windows would be cooler.  It sounds like you sealed them properly.

The master bed bath is taking the hot humid air from the shower and venting it into the bedroom? Even if not, as long as you leave the bathroom door open this would lead to more water vapor in the bedroom and bathroom.  Does the bathroom have a window to the outside?

My guess would be this is more of a vapor issue. Either to much getting in, or not enough getting out.  Is the house too tight and needs more air exchange?

[duncanshannon]

My guess would be this is more of a vapor issue. Either to much getting in, or not enough getting out.  Is the house too tight and needs more air exchange?

That makes the most sense.  The only thing that confused me was the furnace thermostat saying that the humidity was at or within target based on the exterior temp.  35% or so today.  I ordered the thermometer/humidity gauge to put it in the bath/bedroom - to get another reading.

There is a window in the bathroom.

There is a newer fan too. It was oversized for the room.... it does share a common exhaust thru the room (two bathrooms next to each other, two fans that join in an upside down Y in the attic).  I've been wondering if the shared exhaust reduces the effect of the fan in that room.

w/r/t to more air exchange... that makse sense too. When they installed the new system there was no house warp and old windows. now its wrapped and new windows. seems reasonable that perhaps something needs to be adjusted there.  I do leave the FAN on the furnace either low or medium at all times to circulate air.   I did close soome of the runs upstairs to force the warm air to come out on the main level and rise up (so it wasnt too hot upstairs).

hrm....

[bayview]

   I am assuming you have double pane windows . . .    Single panes always get condensation.

   New construction takes time to "dry out".   We purchased a de-humidifier to handle the extra humidity.

//

[John Raabe]

It does seem like you must be getting higher humidity than you expect (higher than 35%). Does the bath vent fan go through the attic and out to a roof or wall outlet hood? IE: does the moisture get all the way to the outside?

If the windows are well rated they must be dual-glazed, argon-filled and perhaps Low-E. You should have a "u-value" of perhaps .4 to .3 (lower is better). The frames, if metal, should be thermally broken between inside and out. If not then you will get condensation on the inside of the metal frames (no matter how efficient the glazing).

Wood, vinyl and fiberglass window frames should be well enough insulated that they will not condense water vapor under normal conditions.

[rdzone]

Here is a good site to explain window condensation.

http://madisonvinyl.com/vinyl-window-condensation.php

[Okie Bob]

I had the same concerns John discussed. First, I'd check to be sure the bath fans truly exhaust outside per John. And second, I'd question the windows, again per John. Double pain, gas filled windows should NOT show any condensation. And, I'd get that one wall insulated, water vapor or not.

[Don_P]

Have you been able to independently check the interior relative humidity? My guess is the furnace's humidistat is out of calibration.

[PEG688]

  Maybe you tighten up the house and you now have some existing  exhaust fan that isn't vented properly.

I'm pretty sure the windows are installed right, like DonP,  I question the furnace sensors , and /  or the unfinished work you have may be allowing moisture in faster than it can get out, so it condenses on the glass which would be the cool-ist surface it hits.

  I'm  not a fan of plastic vapor barriers, I think they trap more moisture than they prevent. From remodels I've done I've seen to many poor results with plastic involved to have any faith in that system or practice.   

[duncanshannon]

Thanks for all the replies - i was getting really stressed worrying about damaging the windows!

Don was right... as far as i can tell the furnace humidity sensor is off.  It auto adjusts based on the exterior temp, but another sensor showed it was higher than the thermostat was reporting.

I manually adjusted the setting to be lower.  that and opening some more air flow in the room took care of it. Whole house is better.

PHEW.

thanks a bunch!

[Don_P]

I had a little reminder the other day that sensor location... or things you don't normally think about can really blow a sensor's mind.

We have a cheapo digital indoor outdoor thermometer/ hygrometer sitting on the kitchen windowsill. It reads the temp inside and out and the relative humidity inside. I had closed the kitchen window but hadn't latched it and it was open the smallest crack. The cold outside air was flowing by the hygrometer sensor but the room temp was still about 65 degrees. Although it was damp outside, high relative humidity for that temperature, it was about freezing. The little instrument was computing RH from the indoor temp. I looked at it and it was reading 4.8%... around here the leakiest of farmhouses, something was wrong. I shut the window and it climbed to 50%.