I will begin this article by stating that if you have condensation on the windows inside of your home, chances are about 9 in 10 that it is not a problem with the windows themselves. Condensation on the inside of your home, if not dealt with, can lead to rotting or moldy wood, bubbling vinyl, or significantly worse issues.
Because the windows and metal in your home are the coldest parts of your home, any moisture in the air is going to gather and condense there. Eventually that condensation is going to run from your windows and hardware down to the wood of your windows, eventually leading to wood that has rotted out. Is this a defect in the window? No. It is an issue with the condensation in your home.
This moisture in the air happens because of many things, showers, doing dishes, running the water, and even breathing causes moisture in the air. It gets even worse if you have a humidifier or air conditioner.
Think about it this way. If you have a glass of cold lemonade on a hot summer day, the glass will form moisture on the exterior. Even many insulated containers will have moisture on the exterior. That is not because your glass is ‘leaking’, or because it is defective, that is just physics.
I would recommend that during the cooler winter months, you will want to keep the moisture in your home at about 30-35%. If you have a higher humidity level than that (you can check with a barometer or your dehumidifier) you will be wiping moisture off of the bottom of those windows multiple times a day.
Don’t fear! If you can’t have your humidity that low for health or comfort reasons, not all is lost. The first thing is to make sure that moisture doesn’t sit on your wood. The second suggestion would be to regulate the humidity in the air with a dehumidifier. You can also install (or use) the exhaust fan system above your stove, and while running water in the bathroom.
If you have a humidifier on your furnace, turn it down or off completely. If you have window blinds, keep them open during the day, as the lack of air flow can keep windows condensing without you even being aware of it.
If you have condensation on the exterior of your windows, that is also not a defect for the same reasons. What happens is that the moisture in the air is high, and the temperature of the glass is below the dew point.
Most energy efficient glass these days can reach lower temperatures than the air next to it, causing condensation. Again, this is not a defect in the glass, but it shows that it is working because insulated glass restricts the flow of heat between the two panes of glass.