Why the inside of the glass gets wet
Natural Resources Canada explains that condensation often occurs in colder weather when moist indoor air meets cooler surfaces, forming water droplets or even frost. The risk increases as the weather gets colder or indoor humidity rises. On a window, it can form on the glass, the frames and sashes, and near the weather seals.
NRCan says occasional condensation does not pose a problem. Excessive condensation or frosting is a sign to reduce moisture production or increase ventilation.
Check the moisture in the house
NRCan’s first steps for reducing indoor moisture include running kitchen and bathroom fans during use, venting the clothes dryer outdoors, not drying laundry or storing firewood in the house, and disconnecting humidifiers. If you have a heat recovery ventilator (HRV), make sure it is on.
A hygrometer can help you monitor humidity. Also note when condensation appears and in which rooms.
Look at air flow at the glass
Air moving across the glass helps keep it warmer, which is one reason heating vents and electric baseboards sit beneath windows in many homes. NRCan notes that deep sills, closed drapes and blinds, and nearby furniture can block that air and let cool air pool at the window.
Check what sits in front of the windows that fog most, and keep registers and baseboards clear.
Household humidity or a window problem?
- Across the house: NRCan treats excessive condensation on the inside of double-glazed windows, outside the kitchen and bathroom, as a sign of too much moisture in the air.
- Along the glass edges: NRCan notes that traditional aluminum spacers contribute to condensation along the edges.
- On the frame or sash: look for rot, mould or staining, worn weatherstripping and air leakage around the frame.
- Between sealed panes: NRCan links this to a broken seal and says it is best corrected by replacing the glazing unit.
Note which windows are affected and where the moisture forms.
When replacement is worth discussing
NRCan describes two approaches: reduce humidity and improve ventilation, or raise the window’s surface temperature by installing more efficient windows. Replacement is worth discussing when frames are in poor condition or condensation persists after household moisture has been addressed. BC Housing notes that a more airtight home may need additional ventilation, and NRCan warns that condensation can get worse after replacement because the old, leaky windows were helping to reduce humidity.
Ask any installer how the proposed windows address the pattern you have noticed and whether ventilation should be reviewed too. Lipstick installs Canadian-made All Weather At Home windows, with dual- and triple-pane options, Low-E coatings and argon fill. Explore our replacement windows in Prince George, or request a free estimate.
