If you are seeing condensation and mold then you have a humidity problem. Buy yourself an hygrometer (humidity gauge). The humidity needs to be below 50%.

Do you have steam heat? Houses that have steam heat can have high amounts of humidity in the winter. If not then you need to figure out where all the excess moisture is coming from.

Mike no offense meant, but around here in the deep south 50% not only makes static sparks which are just maddening, but it also makes the gear run all the time. 60% works, but I should say that is the setting on the dehumidifier, there exists better ways to measure it, I am sure. And I should also add our air can be exceptionally humid, even in winter.

Dehumidifier settings are very inaccurate. An inexpensive gauge purchased on Amazon would be better.

Are they the laser type, prong style, or do they have a wick style sensor? I have seen moisture meters for wood but they can have prongs, which seems odd for measuring a gas like air?

I like the AcuRite humitiy and temperature monitor. They are inexpensive and accurate enough for my needs. I like that it records the high and low humidity temperatures.

You've sealed up the house and in doing so the humidity has no way to escape.

If humidity is high the air has high moisture content. Then if you have a set back period in which you allow temp to fall over night, the temp in the house may be reaching dew point temperature.

Dew point temperature is the temperature at which moisture in the air turns to water. (condensation, rain etc.)

Here's an example of how this might be happening....

Looking at our moisture sensor on the thermometer this morning it reads 55%. Typically it ranges about 50%. Not as much moisture on the window this morning, but at the same time it wasn't as cold overnight. It's not window-related, right?

The windows are forming a tight seal by not allowing moisture to escape, and dry air to enter. It is not a window problem.

Your real problem is mold. If your house is so humid that mold is forming then you need to address it ASAP.

I'm guessing from what you guys are saying, I need to ventilate a bit more in the bedroom. The culprits might be the shower and the fact that it's a small bedroom with us sleeping in it (and often another 1-2 kiddies coming into our bed in the middle of the night). ‍ I'll see about adding a timer or moisture switch in the bathroom. Hopefully that'll help.

@mike Yeah, that's something I need to deal with this weekend. So far I think it's only in our pink pinstripe wallpaper (um, yeah) and window glass.

Thanks, all!

@Austin Air Companie That's a great calculator, btw. Who knew?! For others: http://www.dpcalc.org/

So this post is why Houzz should allow the awarding of gold for future purchases

FYI: my room humidity this morning was 35%. I usually try to keep it around 40% during the winter, else the windows condensate.

First lets discuss condensate. When water vapor hits a cold object it will condensate.

So the windows must be cold. Touch the windows and do they feel cold? There are only a couple ways to address. You can:

a. Try to lower the humidity more and get that dry winter air which is irritating to your throat and lungs.

b. New windows that are not cold to the touch. These are expensive and installation is expensive.

c. Interior storm windows. Fairly inexpensive and not too expensive to have installed, also possible to DIY install. I have installed climate seal storm windows. They have reduced my heating bill quite a bit and keep condensate from forming on the windows. They are also removable for summer and easy to put back on for winter, they pop on and off and seal magnetically.

alexandcynthia,

Probably the best way to understand what is happening is to pick up a thermostat that records temp, humidity levels and if you could find one that records outdoor temps too would help if this is a regular reoccurring problem.

Part of the problem may be your own habit of how you operate your heating system and in some cases your AC system.

I've seen this in a past house but only 1 time that I recall in 15 years of living there. What had happened was it was warm and humid one day and a large cold front came thru so fast that it drop the temp so fast that it hit dew point temp.

The reason why windows get the condensate is because they will always be colder part. So a window has an easier time getting to dew point temperature, which in turn will cause the moisture in the air to condensate on them.

You'll notice by using that calculator that the higher the humidity in the home, the easier it is to reach dew point temperature. This is why you need something to record humidity readings as these can change.

If this occurs only randomly it's probably not as big a problem as you might think. You may need to slightly adjust your habit of where you set your heating or cooling temp.

Probably best way to prevent this would be triple pane windows. But it still might occur under extreme star aligning conditions... such as hot and steamy one day and fast cool down cold front that comes thru your area.

This Building Science Corporation research report on relative humidity is a must-read, I think:

https://buildingscience.com/documents/reports/rr-0203-relative-humidity/view

Basically, with your humidity levels you also need to consider what's going on inside the walls.

Don't panic about condensation on the glass suspecting condensation elsewhere. Unless you have super crappy walls and great windows, it is not going to be a problem. In the olden days, between heating with open draft fire (fireplaces and wood/coal stoves and the introduction of furnaces and boilers and maybe after on the one hand, and introduction of double pane windows on the other, condensation, even ice, on the interior surface of windows was pretty normal.

Yes, reducing interior moisture by use of spot ventilation in the baths and kitchen is going to help. In very cold parts of the world, interior humidity has to be reduced to uncomfortable levels even with great windows. (Plug in dew point 0 F, temperature 65 F. The 0 F dew point would be the outdoor condition, but indoors would be even higher. Consider the temperature of the interior windows might be 30 F if it is -20 F outdoors so the interior would need to be below 27 % to avoid condensation.