Answers

Condensation is caused by high humidity in the home. Often times when you get your windows replaced from single pane wood to a double pane vinyl - you will notice this issue. Older windows tend to have more leaks in them, allowing the excess moisture to escape - therefore it will not form on the window. . . but once you eliminate that escape, the moisture will start to sit on the window. This can be a problem if you have not treated the wood on your sills / trim work - so make sure you do that. Also, get a humidistat and you can google ways to control the humidity in your home. 

Hope this helps! 

In my personal home which has high quality windows, we also suffered condensation. We generate moisture by breathing, cooking, and bathing. If you have casement windows with screens on the inside, you might be surprised just how much those screens prevent convection airflow and keep cooler air closer to the window glass. We solved the problem in our home using a combination of 3 actions.

1) We remove our window screens every winter.

2) We open our window shades all the way every morning and leave them open all day long.

3) We have timers on our bathroom fans and run them for about 4 hours per day in addition to the 10 or 20 minutes of bathing time.

4) Bonus: We always run our kitchen vent fan when we are cooking to remove moisture (and odors) from the house.

I hope that helps. In the end, it's all physics. It's about the dew point, which is the surface temperature at which the relative humidity condenses. It can happen with cheap or expensive windows.

By the way: If there is air leakage around the window, this is going to exacerbate the problem. So doing a call-back to the installer or a 3rd party energy-rating company would help if the other solutions don't work.

Check the flashing on the windows per the manufactures specifications. do not be afraid to call the window compoany for a resource