This is my first post, so I figured I’d make it a good one. I’m a big fan of the breaktime discussions and love FHB. But I’m stumped by a moisture issue in our house.
The concern is that in the past week, there has been condensation forming on the inside of our insulated vinyl replacement windows. No big deal right? Well, this has never happened to this extent in the past two years of living here, so what’s the deal?
Here are some notes that may help solve the mystery –
– this fall I did some thorough air sealing above the bedroom areas in the attic
– there is no insulation in the walls (cir. 1959 split) and only an original to the house foil vapor barrier (retarder?) installed
– forced hot water baseboards…with a new boiler as of one week ago
– two people in the house
– the only bathroom is on the same level with the bedrooms, and it’s properly vented with a brand new Panasonic Whisper vent (works great by the way)
– the second level is kept at a crisp 61 degrees
– the problem persists in the morning
I’m thinking about abstaining from cooking and sleeping in the house for one night, and coming the next morning to see if sleeping, breathing, cooking is creating the moisture.
Also, the day of the new boiler install, the relief valve lifted on the old boiler purging a good 3 gallons into the lower level that was wet vac’d up that day. The next morning I chalked the condensation up to the boiler install and all the hydronics water related activities that day.
I’m concerned and determined to find the source b/c I’m having cellulose blown into the exterior walls on Monday. If there’s a moisture problem, I don’t want the insulation to further complicate things!
Any help, insight or similar past experiences are appreciated – I’m stumped!
Replies
"- this fall I did some thorough air sealing above the bedroom areas in the attic"
That reduces the amount of inside moist air that escapes and is replaced with drier outside air. Thus the moisture level in the house will be higher.
" the second level is kept at a crisp 61 degrees"
The colder the interior air the colder the inside surface of the window will be and thus more condensation.
Get a humidity guage.
Thanks for the reply;
I thought the air sealing may have something to do with it too. Just like you said - all that moisture laden air could escape through those gaps and cracks before...now it's trapped.
I have a hygrometer in the lower level of the house. I use it during the summer months to monitor moisture levels down there.
What would that tell me? That the upper level air is humid?
Regarding the temp; Is there a target indoor temp I should go for that will reduce the chance of condensation?
The most hygrometer measures and displays relative humidity.(Some scientific instruements can measure dew point or wet bulb and along with drybulb compute relative humidity).But using a psychometric calculator or chart you can find the dewpoint and what happens when you change tempature.Here are two online calculators.This one does not work for me, because my java is screwed up. But I think it is the right one.http://www.gorhamschaffler.com/psy.htmHere is another one. But it gives out two much information.http://www.connel.com/freeware/psychart.shtmlLook at the last one. Enter dry bulb (room temp) and RH. It will give you the dewpoint.Then in the next to last one you can enter other temps, but the same dewpoint and you can calculate the new RH if you change the temp.If you change the temp without adding or removing moisture from the air the RH will change, but the dewpoint or absolute amount of moisture will not change.
Edited 10/27/2006 2:18 pm by BillHartmann
Wow, thanks, this is interesting but I don't completely understand it...
so if I use my hygrometer to get a few humidity levels, and I plug the levels into this calculator...then what?
are you drawing a correlation between the outside/inside air temps, RH, the dew point and the condensation? Sorry, I'm just a little confused.
I'm having a combustion safety and blower door done on Monday so that should clear up any possible concerns with the new boiler.
I'm not leaning towards the boiler combustion as a source of the moisture for a couple of reasons; it's on a lower level where there are plenty of surfaces for excess moisture to condense (tiles, windows, etc.) and the temp down there is the same (separate zone.) There are multiple CO detectors throughout the house, but down there is one that has a digital display and the peak recorded level is 0. The installers ran a Testo Analyzer on the new boiler and the CO output was significantly lower than the previous boiler. Does that seem logical?
I see that the 2nd link got left off.http://www.connel.com/freeware/psychart.shtmlNow here are some typical examples.I put in 70* and 35% RH. That might be a nominal level in the lower level.It shows a dewpoint of 41.1*That is any surface that gets below 41.1 will start to get condensation.Now putting in 60* drybulb (roomtemp) and 41.1 dewpoint gives you 50% RH in the cooler upstarirs.But the dewpoint is still 41Now even with dual pain the glass in the window will be colder than the air. And even more so near the metal spacer/seal around the edges.If you keep the air in the room warmer then the glass will also be somewhat warm. So it is farther from the dewpoint.
Okay, thanks for clarifying. That makes sense.
I'll get some numbers and plug them in - I appreciate the input.
Not sure you have problem per se. Try really airing the house out today, before it rains tonight.
Between the boiler work (I assume its vented correctly), and the day/night temp. swings the last couple of weeks, and the brisk 61 degrees, its not too unusual to have some condensation.
Also, try running the heat a little to dry out the inside a little.
It's good to hear someone think this could be normal...It's making me anxious!
It's funny you mention the boiler venting. I can only lean on the installers expertise for venting it properly. Based on what I know I think it's okay. It's getting 'inspected' Monday, the same day as the insulation install.
Right now the boiler has a 5" flue that is venting into a 7" by 7" brick chimney. I'm having a 5" SS flue liner run in the chimney on Monday as well. The liner is going in b/c the new boiler is capable of lower operating temps (104 F) so flue condensation and draft could be an issue in the wrong chimney. Do you think the condesntation could be a venting issue from the boiler?
It's an oil fired system if that helps...
First of all, Welcome to Breaktime!
You didn't state this but I assumed that you have lived in this house over previous fall/winter seasons and this has not occured before.
The one thing that raised a flag for me was "with a new boiler as of one week ago", and the fact that "the day of the new boiler install, the relief valve lifted on the old boiler..."
These two facts lead me to suspect the boiler installation and/or venting could be an issue. The available combustion air, draft developed, venting and burner adjustment all need to be checked/verifed by a profession boiler tech. IF, on the outside chance that the installer did something incorrectly, or your air sealing efforts have inadvertantly caused a draft issue, the moisture is not going to kill you, but the carbon monoxide that comes with it, will.
Condensation forms when, in the "microclimate" within a centimeter or so of a window, the temperature drops below the dewpoint of the room air. The less airflow there is around the windows, the more the temperature drops. Curtains, eg, can trap air and cause a larger temperature drop. Turning off heat in the room can have a similar effect.
You need to find out what the humidity is in your house. It should generally not be above 40% once heating season approaches. Occasionally, though, in the early fall, one can have high daytime humidity and then a significant temperature drop at night, causing condensation that wouldn't occur in the dead of winter. As temperatures dip humidity should likewise, starting to go down at about 40 F outside and going down to 15% or so at zero F. (The exact recomendations for humidity vs temp depend on the construction of your home.)
If the humidity level is "reasonable" then likely the temperature near the windows is the problem. If this is occurring mostly upstairs you may need to raise the temp up there.
Okay, this is really long, and I have posted it previously, but this time of year people are starting to notice indoor condensation so maybe it might help a bit as a bit of a follow up to the great answers that have proceeded it in your thread........
The reason why there is condensation or frost or ice on the interior of your window has a really simple explanation – the surface temperature of the window is below the dew point temperature of the air in your home…that’s it…a very simple explanation.
Unfortunately, the reason why the window surface temperature is below the dew point temperature can become much more complex – but I am going to offer a few thoughts and even throw in a few numbers that I hope might help your situation.
In the summer, when you pull something cold and refreshing out of the refrigerator, and the air is warm and humid, that cold and refreshing beverage container suddenly and quite magically becomes instantly wet – just as soon as it is exposed to the air. What has happened is that the temperature of the container fresh from the refrigerator is below the dew point temperature of the air – which has caused condensation on the outside of that container.
What happens to your windows in the fall and winter is that the surface of the glass is below the dew point temperature of the air in your home – which is causing condensation on the surface of that glass.
Dew point is defined as saturation vapor density...or put in simpler terms, when the air reaches 100% relative humidity and can hold no more moisture.
Relative humidity is, well, relative.
Relative humidity is a comparison of the actual vapor density versus the saturation vapor density at a particular temperature. Put a bit more simply, dew point is 100% relative humidity or the point where the air - at that temperature - is no longer able to hold any more moisture. If the air has reached vapor saturation (100% relative humidity), then the air will release moisture...be it on the outside of that cold beverage container in the summer time, or be it on the interior glass surface of your windows in the winter time, it makes no difference. If the surface temperature happens to be below freezing, then that moisture becomes frost or even ice.
In order to stop condensation from forming on the surface of a window, you either have to lower the dew point temperature of the air in your home to a level below the dew point temperature of the window surface, or you have to warm up the window surface to a temperature above the dew point temperature of your home, or a combination of both.
Lowering the relative humidity of the air in your home MAY have absolutely no effect on controlling window condensation…and I bet that that statement is a bit of a surprise to some folks…it is true however because there are two ways to lower relative humidity – increase air temperature or decrease moisture content. If you increase the air temperature you will lower the relative humidity but you will not change the dew point - which is based on the amount of water vapor in the air and is not based on the temperature of the air.
The amount of moisture in the air is measured in grams per cubic meter, which is kind of nice for our metric folks but not so nice for our non-metric folks; but the metric version is much easier on the calculator than the English version. However, in the interest of making this stuff easier to understand for all of us non-metric types, I am going to use Fahrenheit rather than Celsius temperatures in the calculations.
Okay – consider your home at 65 degrees F and with a relative humidity reading of 40%. There are 6.25 grams of water in a cubic meter of air in your home in that particular scenario - which then equates to a dew point temperature of 38 degrees F. So at 38 degrees the air will be at 100% relative humidity or at saturation vapor density.
Now, if your neighbor keeps her house at 75 degrees, but she also has 6.25 grams of water per cubic meter in her air, then the relative humidity in her home is 29% - versus your 40%. But, and here’s the kicker, the dew point temperature in her home is still 38 degrees.
While the relative humidity in her home is much lower than is the relative humidity in yours; if the surface temperature of the windows in her home is 35 degrees she will have condensation on those windows…yet if the surface temperature of your windows is 40 degrees – only five degrees warmer – you will not have condensation on your windows.
So, while her handy humidity gauge reads (correctly) only 29% RH – she has a condensation problem.
While your handy humidity gauge reads (correctly) 40% RH – you don’t have a condensation problem…SWEET…well, for you anyway, not her.
If your home hygrometer measures the relative humidity in your home at 60% while the temperature of your home is 70 degrees, you will have a dew point temperature of about 51 degrees – meaning that if the temperature of the window surface is below 51 degrees then you will have condensation - so now we talk a little more specifically about windows.
The interior surface temperature of a single lite of glass, when the temperature outside is 0 degrees F and the inside air temperature is 70 degrees, will be about 16 degrees.
Add a storm window on the outside and the surface temperature of the inside lite jumps up to about 43 degrees – a huge improvement.
But these are center-of-glass readings and not the temperature readings at the edge of the window where condensation usually forms. A typical clear glass dual pane window is going to have center-of-glass temperature reading pretty much the same as a single pane with a storm – something that is often claimed (correctly) by folks who advocate refurbishing windows rather than replacing (something that I am not going into here – I am NOT advocating either replacement or restoration in this post. It is long enough and detailed enough already without opening that particular can-of-worms!)…
However, if that dual pane has a LowE coating and an argon gas infill then the center-of-glass temperature will be about 57 degrees – a 14 degree improvement over a clear glass dual pane or a single pane with storm window – but again, and more importantly, there will be a comparable edge of glass improvement as well, particularly if the IGU (Insulating Glass Unit) was manufactured using a warm edge spacer system. Also, the dual pane is going to have desiccant between the glass layers. Desiccant absorbs moisture keeping the inside of the dual pane system very dry.
The advantage? If it gets cold enough outside, the temperature in the airspace between the lites can get very low. By keeping that space dry, it helps to keep the dew point temperature very low as well; something not always possible when using a single pane and storm window.
Although a single pane with a good and tight storm window can help the interior lite to avoid condensation (when compared with a single lite and no storm), the storm window itself will frost up when the temperature is low enough – at a temperature usually well above the temperature that will cause the dual pane to ice up. It is unavoidable given the right circumstances
So what does a window temperature of 57 degrees mean? Well, as I mentioned earlier a home kept at 70 degrees with a 60% relative humidity has a dew point temperature of 51 degrees so it is unlikely that there will be condensation problem on those particular windows despite the relatively high relative humidity in the home.
But what happens to the dew point if you keep your home at 70 degrees and you have a 65% relative humidity? Well, for one thing the dew point has jumped up to 57 degrees which we have already noted is the same as the window temperature. For another thing, anyone with 65% relative humidity in a home at 70 degrees has way too much moisture in their air and they are in serious need of some sort of ventilation system – or at least several good exhaust fans!
Somewhere back in this post I mentioned that lowering the relative humidity in your home may not help control condensation…that is still true…IF the relative humidity is lowered because of an increase in temperature. But, lowering the relative humidity by removing water is a different story because in that case you will also be lowering the dew point as you lower the relative humidity and that WILL help to control condensation on your windows.
"Lowering the relative humidity of the air in your home MAY have absolutely no effect on controlling window condensation…and I bet that that statement is a bit of a surprise to some folks…it is true however because there are two ways to lower relative humidity – increase air temperature or decrease moisture content. If you increase the air temperature you will lower the relative humidity but you will not change the dew point - which is based on the amount of water vapor in the air and is not based on the temperature of the air. "But raising the air tempature will also raise the tempature of the surface where you are getting condensation.How much it raises it depends on the circumstances.
But raising the air tempature will also raise the tempature of the surface where you are getting condensation.
How much it raises it depends on the circumstances.
True, which is the reason for the emphasis on "may" in the original post. But ultimately, lowering the level of moisture in the home has a better chance of affecting condensation than does raising the temperature - unless the original temperature was unreasonably low.
The edge of a window can get darn cold in the winter (depending on location of course) and raising the temperature in the home may have very little effect on that edge-of-glass temperature.
Edited 10/29/2006 8:56 pm ET by Oberon