To reduce fogging on the room-side of household windows, lower indoor moisture at its source and keep warm room air moving across the glass. Cold glass makes condensation more likely, so a single humidity target—or simply opening a window—cannot guarantee a clear pane in every rainy, cold-weather condition.
First, find out where the moisture is
Wipe the glass, frame and sill dry, then check where moisture returns. Indoor condensation forms when moist room air meets a colder surface; showers, cooking, indoor clothes drying and humidifiers can all add moisture to that air.
As an Amazon Associate I earn from qualifying purchases.
- Room-side moisture: Indoor humidity and a cold pane are likely contributors. Focus on moisture sources and airflow.
- Moisture between panes: This can indicate a failed insulating-glass seal. Wiping the room-side glass will not fix it; have the window or sealed glass unit assessed.
- Moisture on the outside: Exterior dew can form on high-performance windows during cool, calm, humid conditions. It is different from indoor condensation and does not by itself show that the window has failed.
Rainy weather does not, by itself, establish that rain is leaking through the window. If water appears around the frame or wall rather than as a film or droplets on the room-side glass, investigate possible water entry as a separate issue.
Reduce moisture where it is produced
Use exhaust fans for showers and cooking
Run the bathroom fan during showers and afterward, and use the kitchen exhaust fan while cooking. Check that each fan exhausts outdoors; a fan that only moves air elsewhere in the home does not remove that moisture from the building.
#1 Best Overall
- Save on energy costs during cold weather months. Duck Max Strength shrink window film is puncture-resistant and two times thicker than standard window kits to create an airtight seal inside your home to block drafts and cold weather
- Easy-to-install roll of shrink film means no measuring needed - once applied, cut film to size
- Tools needed: scissors and hair dryer. For best results apply window films indoors on clean and dry surfaces, including painted or finished wood, aluminum or vinyl
- After installation, crystal clear and transparent window film is easy to see through. Once season is over, the window kit removes easily
- Window Kit includes 1, 62" x 210" roll of shrink film and 1, 0.5" x 84' foot roll of tape; Can insulate up to 5 standard sized 3' x 5' windows
Vent the clothes dryer outdoors
A clothes dryer should discharge outdoors. If laundry is drying indoors, it adds moisture to the room air; reduce indoor drying when condensation is a recurring problem.
Adjust humidifiers and check for other moisture
If a humidifier is running, lower its output or turn it off temporarily and see whether condensation changes. Look for leaks or other persistent dampness as well: a dehumidifier can remove moisture from room air, but it does not repair a leak or a failed window seal.
Rank #2
- Designed for interior use on windows
- Accommodates up to 4 standard sized windows
- Shrinks with hair dryer and applies with included double-faced tape
- Each sheet measures 62 in. L x 42 in. W
- Helps R-value increase up to 90%
Use humidity readings as a guide, not a guarantee
The U.S. Environmental Protection Agency advises keeping indoor relative humidity (RH) between 30% and 50% where possible, and below 60% if possible. Health Canada also recommends 30%–50%. Those ranges are useful general guidance, not a promise that windows will stay clear: condensation risk also depends on outdoor temperature, glass temperature, window construction and airflow.
Natural Resources Canada gives different maximum indoor RH values for a home at 21°C (70°F), depending on outdoor temperature and window type. The figures below are that agency’s guidance, not universal targets for every home or window.
Rank #3
- This product adds a great value
- Product is highly durable and very easy to use
- This product is manufactured in China
- If you want to open your windows in the warmer months, you'll need to take it off. Otherwise, sunlight and normal stress can also make the tape fail eventually. For a good seal, it's probably best to re-apply them every year.
| Outdoor temperature | Older-generation double-glazed low-E | Double-glazed | Double-glazed low-E | Triple-glazed low-E |
|---|---|---|---|---|
| 0°C (32°F) | 50% | 58% | 70% | 81% |
| -10°C (14°F) | 34% | 44% | 59% | 74% |
| -20°C (-4°F) | 24% | 34% | 50% | 67% |
| -30°C (-22°F) | 15% | 25% | 42% | 60% |
| -40°C (-31°F) | 10% | 18% | 35% | 54% |
Use an indoor humidity meter (hygrometer) to track RH while you adjust moisture sources. Readings help show whether indoor humidity is high or changing; they cannot account on their own for a particularly cold pane or restricted airflow.
Improve airflow along the glass
Room air that can circulate across the pane helps reduce condensation. Natural Resources Canada notes that proper air circulation near windows is necessary to minimize it.
Rank #4
- Save on energy costs during cold weather months. This rolled window kit creates an airtight seal inside your home to block drafts and cold weather
- Easy-to-install roll of shrink film means no measuring needed - once applied, cut film to size
- Tools needed: scissors and hair dryer. For best results apply window films indoors on clean and dry surfaces, including painted or finished wood, aluminum or vinyl
- After installation, crystal clear and transparent window film is easy to see through. Once season is over, the window kit removes easily
- Window Kit includes 3, 62" x 210" rolls of shrink film and 3, 0.5" x 54' foot rolls of tape; Can insulate up to 15 standard sized 3' x 5' windows
- Open curtains or blinds enough to let room air reach the glass.
- Move furniture away from the window if it blocks circulation.
- Keep baseboard heaters and HVAC vents clear so they can circulate air toward the window.
Dry wet glass, frames and sills rather than letting water sit. Persistent surface condensation can damage window finishes and nearby materials.
Choose the next step based on what is causing the fog
| Approach | What it addresses | When it makes sense |
|---|---|---|
| Bathroom or kitchen exhaust; outdoor dryer vent | Moisture at its source | Use when showers, cooking or laundry are adding moisture indoors. |
| Hygrometer | Measures indoor RH | Useful when you need to see whether humidity changes as you alter household habits. |
| Dehumidifier | Removes moisture from room air | Consider for a persistently damp space after checking moisture sources and ventilation; it will not fix leaks or a failed sealed unit. |
| Open coverings and clear nearby obstructions | Air movement at the glass | Use when curtains, furniture or blocked heating and ventilation outlets restrict circulation. |
| Window improvements or replacement | Can raise the interior glass temperature over the long term | Consider only after diagnosing the window and moisture conditions; construction features matter more than a general promise of fog-free glass. |
Natural Resources Canada identifies features associated with better energy performance and less condensation than ordinary models: triple glazing, low-emissivity (low-E) coatings, inert gas between panes, thermally improved spacer bars, insulated frames and greater airtightness. Upgrading is a longer-term option, not a substitute for controlling indoor moisture or investigating water entry.
Best Value
- Save on energy costs during cold weather months. Duck Max Strength shrink window film is puncture-resistant and two times thicker than standard window kits to create an airtight seal inside your home to block drafts and cold weather
- Easy-to-install roll of shrink film means no measuring needed - once applied, cut film to size
- Tools needed: scissors and hair dryer. For best results apply window films indoors on clean and dry surfaces, including painted or finished wood, aluminum or vinyl
- After installation, crystal clear and transparent window film is easy to see through. Once season is over, the window kit removes easily
- Window Kit includes 2, 62" x 210" roll of shrink film and 2, 0.5" x 54' foot rolls of tape; Can insulate up to 10 standard sized 3' x 5' windows
When wiping is not enough
If condensation is persistent, heavy, damaging the frame or sill, or appearing between panes, investigate the moisture source and window condition rather than repeatedly wiping without a diagnosis. Surface condensation points toward a combination of indoor moisture and a cold surface; between-pane moisture is consistent with a broken insulating-glass seal and may require replacement of the insulating-glass unit.
Opening windows is not automatically helpful in rainy weather: outdoor air may itself be humid. The EPA’s moisture guidance qualifies ventilation by opening windows when it is not humid outdoors. If indoor humidity remains high, prioritize source control and appropriate exhaust, and consider a dehumidifier if the room stays damp.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
Recommended Free Tools
