Inside Condensation - Wood Stove?

[SLOBuds]

We have a small cabin in central California. Every morning we get a large amount of condensation on the inside of the windows. There doesn't seem to be condensation on the walls. No fog or water on the inside mirrors. But all of the windows are completely dripping wet.

The amount of water seems abnormal to me. It's not just a little bit of 'fog' - very large droplets.

Is something causing this which I should be taking action against?

I have a wood stove that is vented to the outside. And I have what seems to be normal wall insulation. And the windows are covered on the inside with 'duet' blinds plus sheer curtains.

Thanks.

Martin Petersen

[chrisjbell]

Hi Martin -

Do you have single pane windows? Those will tend to really draw moisture out of the air and create condensation on your windows. Even double panes can do the same, but single panes are notorious for that kind of behavior.

My guess (note: just a guess [img]/forums/images/icons/wink.gif[/img]) is that you have a nice warm interior and a chilly exterior and you're just getting moisture from the temp difference. Cabins (as opposed to houses that are more frequently sealed and insulated) also tend to have more air exchange between inside and outside so I expect you are getting a fair amount of outside air (at this time of year generally high in moisture) coming in and when you heat it up with your wood stove it creates condensation on the windows.

I tend to heat my wood stove up pretty good. I really like a warm house [img]/forums/images/icons/smile.gif[/img] and keeping it stoked for a few hours makes it nice and toasty. But my house is so well insulated, with double pane windows, that I have a pretty low humidity level and try to offset it with a kettle on the stove filled with water.

Of course, I could be totally wrong [img]/forums/images/icons/tongue.gif[/img]....

[beenthere]

Chris
Your explanation was good (regards the window panes) but 'not so good' when explaining the moisture in the air. Cold (outside) air holds less moisture so the 'relative' humidity is high. Warm (inside) air holds more moisture so the 'relative' humidity, especially when adding heat, is usually low in the house in the winter (and, like you, we add moisture to bring the relative humidity up).

However, for the same reasons, when the inside warm air gets over close to that window pane (uninsulated, single pane, whatever), the air cools and can't hold the moisture, so it condenses on the glass.

Dry wood picks up moisture when outside in the cold air because the relative humidity is high, and the same wood will dry out when brought inside a heated house because the warm air has a low relative humidity.

When a cold front (cooler air) moves through and hits warm, moist (high humidity) air, often it causes rain or snow. Same principle.

Hope this helps. Martin needs to keep the warm air inside his house from reaching the window panes, or add storm windows on the outside, or lower the humidity in the house. He didn't say if he was running a humidifier, nor whether he was venting the clothes dryer, or the shower. There are several things in a house that will add moisture to the air.

[Al_Wa]

<font color="blue"> Cold (outside) air holds less moisture so the 'relative' humidity is high. Warm (inside) air holds more moisture so the 'relative' humidity, especially when adding heat, is usually low in the house in the winter (and, like you, we add moisture to bring the relative humidity up).
</font color>

I think this is a little "upside down". The higher the moisture content the higher the relative humidity.

Relative humidity may be defined as the ratio of the water vapor density (mass per unit volume) to the saturation water vapor density, usually expressed in percent:


Relative Humidity (RH) = (Actual Vapor Density)
--------------------
(Saturation Vapor Density)
X 100%

Relative humidity is also approximately the ratio of the actual to the saturation vapor pressure.


RH = (Actual Vapor Pressure)
--------------------------
(Saturation Vapor Pressure)
X 100%

Actual vapor pressure is a measurement of the amount of water vapor in a volume of air and increases as the amount of water vapor increases. Air that attains its saturation vapor pressure has established an equilibrium with a flat surface of water. That means, an equal number of water molecules are evaporating from the surface of the water into the air as are condensing from the air back into the water.

[Hakim]

Hey you guys!

I never expected I was going to get a distance learning Engineering Degree in Water Vapor --- but I did! Thanks!

I used to have this exact same problem in three different houses in NY. I never was able to solve it. Now I almost feel like moving back there, just to try out all my new "knowledge."

All kidding aside, you all are making really terrific contributions to our CountryByNet.com knowledge base. Thanks, sincerely, and keep up the good work. [img]/forums/images/icons/grin.gif[/img] [img]/forums/images/icons/grin.gif[/img] [img]/forums/images/icons/grin.gif[/img]

[beenthere]

Al-WA
Upside down?

My point being that relative humidity is "relative" to what moisture the air will hold at a particular temperature. The same "moisture" in a specific volume (i.e. cu.ft.) of warm air will cause a higher relative humidity if that air is cooled (and the moisture will condense out as the temperature gets colder, because cold air cannot hold much moisture).

Dew point, wet bulb temperature, dry bulb temperature, etc. are all things involved in measuring the relative humidity.

The reason for a vapor barrier on the warm side of insulation in a house has to do with warm air on the inside, and cold air on the outside, and keeping the moisture from passing to the cold air, thus avoiding condensation and getting the insulation wet (then it is no good as an insulator). If no vapor barrier, the moist air reaches the siding and condenses, causing wet wood, and then rot and decay. Venting the moist, cold air helps some. Carpenter ants are a good sign that there are moisture problems in the wood in a house, caused by poor venting and poor vapor barrier. Carpenter ants only go to wet wood. (sorry this got so far off track)

[Pat]

Hakim, Just in case you weren't copmpletely confused by the preceding, allow me to complete the job! The glass is cooled by contact with the cold external environment. If you are single glazed then the problem is worse but even double glazing can have the problem, just not so bad. The temperature of the glass goes below the dew point and water condenses out on the cold glass surface like it does on a glass of ice water.

Essentially, YOU, are the problem. What can you do to alleviate the problem? Quit breathing and stop perspiring! Cooking, bathing, etc. also contribute to inside moisture. There are downsides to this condensation, stuff like rotting out window sills. Not all the condensation is always visible, some of it may be behind lose fiting window triim etc. Water and wood equals rot!

If you have a vent free propane or natural gas heater GET RID OF IT! If you don't have a range hood that vents to the outside, install one and always use it at least on low every time you light a gas range/oven or cook on any stove, gas or electric. If you drink hot beverages or coffee or tea, make them under the range hood to remove the steam from the cabin. If you don't have a good exhaust fan in the shower area, install one and ensure it vents to the outside, not the attic. Install a timer to operate the fan in the bath area so you can give it a twist and let it run 10 minutes or so after you finish bathing. It takes longer to get rid of the moisture than most folks think.

If you occupy the cabin enough to make it practical consider installing an ERV or HRV (energy or heat recovery ventilator) so you can get more air changes without throwing away so much conditioned air. Of course if you don't have A/C and the cabin leaks air like a sieve in winter, then you don't need one untill after you tighten up the cabin by caulking things up.

Burrning more wood, more hours of the day will help but not eliminate your window's night sweats. Not heating the cabin sufficiently at night while it is occupied is a major contributor to condensation. The water source is your human activity and biofunctions. The condensation is due to sufficiently cold windows and moist inside air. Consider getting more energy efficient windows. A good dual or even triple glazed window with argon fill, full thermal breaks (if aluminum) will reduce the problem and perhaps eliminate it in conjuction with other moisture control measures like bathroom exhaust fan with timer and a range hood.

It is a good news bad news story. During the day the cabin air is likely already pretty low in rel humidity. Maybe lower than is comfortable (dry chapped skin, nose bleed, whatever) but at night when it cools off the relative humidity soars a bit, especially as a previous poster pointed out, against the chilled glass. Heavy drapes are often used to insulate windows. It helps warm the room at night but will allow the glass to chill easier and condense more water.

You con't need to buy Pella or Anderson windows at thousands of dollars to get good windows. Shop price, warranty, and performance... NOT NAME. I'd start with the cheapest and most likey to solve the problem fixes. Range hood and bathroom exhaust fan with timer. That can really help. If it doesn't help eough then you need to run more heat at night and or get higher performance windows.

Good luck,

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[Hakim]

Pat,

Thanks for the post-grad short course! [img]/forums/images/icons/grin.gif[/img]

Seriously, this info will save anyone a ton of time and expense "trying out" various solutions. I wish, I had all this when I had my farm house and later on, a big log house. Would have saved me untold aggravation.

Thanks again for your informative posts.

[Pat]

Hakim, I am pleased to try to help you and only regret that due to my other commitments that I can't take the time to make a field engineering visit and stay in the cabin for a few days to study the problem and ensure a more complete recommendaton.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[egon]

Heck; I am still not sure what the problem is, but move to a cold area with dry air and these problems will almost go away by themselves.

Better yet; move into a breathable tent with a fly. Solve all the problems.

Egon