The optimum zone of the relative humidity of one's home at any given time is between 40% and 60%. This is the range to ensure that the humidity does not damage one's health or one's furnishings, in either direction.
My hygrometer notified me that the indoor RH was only 20%. This is the lowest figure that the hygrometer is capable of outputting, so the actual RH could be even lower than that. (I have not found an inexpensive hygrometer that is capable of displaying RH levels below 20%.) Naturally, this reading spurred me to turn on the humidifier.
I have an Aprilaire central humidifier next to my furnace. It is an old unit (around 25 years old), but it still functions. The humidifier control panel has a knob with a range of 15% to 45%. Because of the guideline mentioned in the first paragraph, I set the humidifier to the maximum setting of 45%. My thermostat is set to 72° F.
Here is info I just collected with the inexpensive hygrometer device (currently at 11 PM at night):
Current indoor temperature: 70° F
Current indoor humidity: 51%
Here is the current info from Weather.com:
Current outdoor temperature: 9° F
Current outdoor humidity: 81%
Now, on to the issue...
Most of my double-pane windows currently have significant condensation on them. The condensation is on the inside of the windows, not between the panes. Some windows are practically coated edge-to-edge in water droplets, requiring several paper towels to absorb it all. I wipe it off, and the condensation fully returns within an hour or two.
Gravity makes the condensation drip down the length of the window, which gets absorbed by the surrounding wooden window trim. This has resulted in trim that is pitch black in some areas, an indicator of dry rot, I assume. I touch the wood and I can feel that it is very wet.
Wanting to prevent dry rot from occurring and further destroying my trim, I tried to find a fix online. I found this article from Star Tribune, the largest newspaper in Minnesota. Excerpt:
The following list, supplied by the Minnesota Department of Public Service, is based on a double-glazed window and an indoor temperature of 70 degrees. You will notice that the lower the outdoor temperature, the lower the indoor humidity should be.
• If outside temperature is 20 to 40 degrees, humidity indoors should not be more than 40 percent.
• If outside temperature is 10 to 20 degrees, humidity indoors should not be more than 35 percent.
• If outside temperature is 0 to 10 degrees, humidity indoors should not be more than 30 percent.
• If outside temperature is 10-below to 0, humidity indoors should not be more than 25 percent.
• If outside temperature is 20-below to 10-below, humidity indoors should not be more than 20 percent.
• If outdoor temperature is lower than 20-below, inside humidity should not be more than 15 percent.
(The article did not specify, but I assume that the "outdoor temperature" is the outdoor temperature without including the windchill factor.)
Huh? I thought that an RH below 40% was too dry for one's body. But, according to the above prescription, based on the outdoor weather conditions, my current indoor RH should not exceed 30%. In some extreme cases, it should be as low as 15%.
Why does condensation form on the inside of my windows in the winter?
Why does the amount of condensation seem to significantly increase at night? My thermostat and humidifier settings are constant.
The recommended RH range for one's health or one's furnishings contradicts the recommended RH range to prevent condensation on windows. How do you choose which guideline to abide by? In an indoor environment with an RH of 30%, I would be breathing in dry air and drying out wood furnishings. Shouldn't one's health take precedence over the development of window condensation?
Is there anything I can do to stop the formation of condensation on windows, besides decreasing the indoor RH level? (I suppose that I could periodically walk from window to window, wiping off the condensation with a towel, but I'd have to do this so regularly that it would nearly be a part-time job.)