Typically increased condensation on windows may result from one or more of: a change in temperature difference between indoors and outdoors, increased indoor humidity, a decline of the windows' insulating qualities.

Have you been doing more cleaning lately? That will put more water vapor into the air.

How's the exhaust on your clothes dryer?

Are you cooking more? It's not just boiling down soups. A standard gas stove with 3-4 burners and the oven going can produce as much products of combustion as a 40 gallon gas water heater. Larger "pro" style ranges can produce even more. However, unlike the WH, stoves aren't vented to the outdoors. So a heavily-used gas stove can release quite a bit of water vapor (and other unpleasant things) into your home's indoor air.

Have you checked for a leak in your furnace flue and/or heat exchanger?

Most homes don't need a dehumidifier during the winter. Cold outdoor air can't hold as much moisture as warmer air. As that air infiltrates into the house and is warmed, its relative humidity gets very low. So it's possible that your situation will improve after some days.

I cleaned my clothes dryer exhaust this fall and had my furnace inspected for routine maintenance about two weeks ago and there were no issues. The house cleaning frequency has not changed nor has the frequency and cook time of home cooked meals. I do greatly appreciate the ideas.

Tons of info here on condensation if you do a search.... If the windows have not exhibited this problem (to this degree) in the past, they can be removed as a variable. Its highly unlikely that poor window performance is the culprit either way. Get a hygrometer and take some readings of the RH in the home. Then visit dpcalc.org to see where it needs to be based on the temperatures. Window treatments are big, obvious cause, but the things that others have alrady mentioned can be contributors as well.

I do have a humidifier attached to my furnace. I may try to lower whatever it is set at. This might help the issue.

Step 1 - Turn off humidifier.

Step 2 - Figure out what the humidity inside the home is right now.

That's a lot of condensation you show in your photos. FWIW, the only time I've seen similar amounts in my own home is when the indoor humidity was very high. Specific instances I can think of are a vaporizer running for a sick person in the same room, multiple showers in a short period, and unusually aggressive cooking such as boiling down soups, reducing maple syrup, or preparing a holiday meal. With that kind of condensation going on, the house should FEEL humid.

But you say this happens mostly at night. That has to be a clue. What's different at night in your house?

It gets colder at night DavidR, that and some people close their blinds. Perhaps we should consult with Watson on some additional theories.

Get something like this. Your humidity should be around 25 - 30 %

Blinds are closed at night (faux wood 2 inch). Water bill has not been higher, so I don't think there is a leak somewhere in my house causing issues. Again, showers have not been long and the fan is always running and I don't do any boiling down of broths when I cook. The showering is in the morning, not at night, so why at night does the condensation buildI have no clue. I understand that it's cooler at night, but it's still pretty cold in the daytime, too. The blinds are generally open in the day time, and there is still condensation on the window but no where near the amount that is found when I wake up in the morning.

I will be buying a temp/humidity device when I get off of work. I saw an online article about calibrating it by placing the device in a sealed bag of salt water over night in such a way that it is not submersed. Is this calibration recommended?

I use this monitor. I don't know if the circuitry is identical, but the display looks similar to the one Geoffrey pictures, except for the different "appropriate humidity" icon at the top right. I wouldn't be surprised if they come from the same Chinese factory.

The online reviews mostly say they're fairly accurate. I have 2 of them, and when they're placed side by side, they're within 2 percentage points of each other. So I haven't worried about calibration. I don't think they can be calibrated anyway.

The link is for illustration, and isn't meant as an endorsement of either the product or the vendor.

Are you closing the blinds tight?

Is your bathroom exhaust fan actually working (moving air from inside to out, not just making noise)? Somehow your house humidity is way too high. If you're running a humidifier on the furnace check to see that its control is still working (it should not run at all with that level of humidity!).

While I agree that the indoor humidity is likely too high, and the blinds should be left open an inch or two, there also comes a time when you need to look at the windows' age and condition. In my home, I was careful with indoor humidity and kept the blinds open an inch or two. I live in the same region as the OP. I had the pooling of water on the sill, and even indoor ice dams in the morning. It was the windows. They were done. The frames were rotted too. I replaced the windows. I no longer have the indoor condensation and ice dams. Not the drafts either, which I had become so accustomed to, I hadn't realized how much warmer my rooms could be. I was amazed when they were gone.

Just a quick update. Came home and there was still condensation on the windows, but not much pooling on the sill. Checked the furnace and saw the humidifier is at 35% (max is 40%). I set it to 0. Woke up this morning with some condensation on the bottoms of the windows, but not really any pooling on the sill. I also left the blinds up a couple inches last night. As the house dehumidifies from the humidifier being turned of, we'll see how wet the bottom half of the windows become.

The bathroom fans will be replaced this or next weekend. They are from 2002 when the house was built. I've been wanting to change them anyway. This just gives me more motivation to do so.

I do not think it's a window issue because it's happening on all windows.

I'll check the air return but I do not think that's the issue. All the ducts were cleaned 2 years ago and I scheduled a routine furnace check up a couple weeks ago which had nothing pop up as concerning... just a water filter replacement for the humidifier. I'm guess the maintenance guy also bumped up the humidifier, too, which led to a lot of excess humidity.

To clarify my comments above, better windows would help. The other main factor besides RH in the presence of condensation is the temperature of the surface in question. A more efficient window with fewer air leaks and a better insulating glass pack will have a warmer surface, and therefore less condensation at the same RH reading... That said, in most cases there are other issues going on with excessive condensation such as you have, in either RH that is too high for the given exterior temps, or something blocking the windows (window treatments, furniture, etc) from warming up via the heated interior air. All of the other suggestions made in this thread are possibilities that affect one of those two things (make the window colder or RH higher).

I think you are on the right track though. Again, I'd recommend getting an accurate RH reading in the home to truly assess this, as dial on the humidifier is not going to offer that. Turn that device off, make sure the blinds are open as much as possible while still providing the privacy that you need, make sure bath fans are sufficient, cold air returns and heat registers are not blocked, etc. On the bath fan aspect, if you are planning to replace them I'd recommend digging into this a little deeper as this could be an area to solve a chronic problem if the easy stuff doesn't do so. Constant run bath fans like the Panasonic whisper series have a super quiet constant run motor and a second that runs on a typical switch for showers etc. We use these in some cases where homes are sealed up a little too tight where indoor air quality may become a concern... I am getting a little ahead of things with this though, again, get an RH reading, get some warm air circulating on those windows, and see where we are at.