Ice formation in the interior of windows.

Without knowing anything about the windows you have and the conditions inside around the windows there is one really only one thing you can say for sure - the inside of that window has dropped below the freezing temperature. That might sound silly, but that's the only think you can tell from what you are seeing. The next real question is why am I seeing ice, and that question can have a few different answers. First off, understand that windows are insulators from the outside climate, but they are not very good at insulating (even some of the best current windows are not as good as a wall at insulating). You will almost always see the influence of the cold (or hot) at the windows. The only source of heat for your house is provided by the methods that you have to heat your home (furnace, wood stove, electric heat, fireplace, etc.). This means that the heat from your home must keep the window above the freezing point of water to keep that ice from happening. The better the window is at keeping the heat in (insulating), the easier it will be for the heat from your home to stay inside and keep the window "warm". It has been very cold lately and that comes in at the windows the easiest. The thermostat for your house is located centrally, that means it may be 70 at the thermostat but it is almost always colder at the outside of the house. 1. Old windows, poorly insulating. 2. Old/New windows that have weather stripping worn out. 3. Newer windows that are not fitting properly. 4. Blinds/drapes/shades/shutter blocking heat from getting to your window. 5. Doors closed into rooms keeping the cold air in the room before the thermostat changes temperature enough to call for heat. 6. Heat vents blocked around windows (usually underneath the window) or missing entirely from a certain area. It could be one or combination of all of these things. At these extreme temperatures, excessive humidity can also show much quicker on colder surfaces.

Hi Venky, Thanks for reaching out. Seeing ice on the inside of your windows can definitely be unsettling, so your concern is understandable. The key thing to know is that ice forming on the interior surface of a window does not automatically mean there is a leak or a failure. What it tells us is that moisture in the indoor air condensed on the glass and, during very cold conditions, froze. This usually happens first at the edges and corners of the window, because those areas are naturally the coldest parts of the glass. Windows don’t create moisture. They reveal it. In winter, especially during periods of extreme cold, warm indoor air always contains some humidity from normal daily life like cooking, showering, and even breathing. When that humid air comes into contact with cold window glass, condensation can form. If the glass temperature drops low enough, that condensation can freeze and appear as ice. This is often influenced by conditions around the window rather than a defect in the window itself. Things like tightly closed blinds or curtains overnight, limited airflow to the glass, shaded windows that receive little sunlight, or indoor humidity levels that are slightly high for the outdoor temperature can all contribute. Even a home that feels warm overall can still have colder zones near exterior windows, especially during severe cold. That said, there are situations where ice or moisture should be investigated further. We would recommend inspection if you notice any of the following: Fog or moisture trapped between the panes of glass A noticeable draft or cold air coming from the frame or edges Ongoing water accumulation that leads to staining or damage around the window If the ice is on the room side of the glass and wipes away once conditions improve, it is usually related to humidity and airflow rather than a leak. To help reduce this, a few simple steps often make a noticeable difference: Allow warm room air to reach the glass by opening blinds or curtains slightly Run kitchen and bathroom exhaust fans longer after use Temporarily reduce humidifier settings during very cold weather Ensure heat vents near windows are not blocked If you’d like, feel free to share a bit more detail about whether this is happening on several windows or just a few, and whether the moisture wipes off the glass or appears trapped. We’d be happy to help you determine whether what you’re seeing is a condition-related issue or something that needs closer attention.