Whether or not keeping your windows closed will keep your house cooler depends on several factors. In general, closing windows during the day can help reduce heat gain from sunlight and warm outdoor air. However, at night it is often better to open windows to allow cooler outdoor air in. Strategic window use along with other cooling methods like fans, shades and AC can optimize indoor comfort.
How Do Windows Impact Home Temperature?
Windows impact home temperature in a few key ways:
Solar Heat Gain
Sunlight shining through windows heats up the air and objects inside a home. This is known as solar heat gain. The more windows a home has, especially on the south and west sides, the more solar heat gain occurs.
Conducted Heat Gain
When outdoor air is warmer than indoor air, heat will conduct through windows and raise indoor temperatures. Windows have lower insulation values than walls so heat is easily transferred through them.
Infiltration
Open windows allow outdoor air to infiltrate into a home. This brings in heat and humidity along with it. Air infiltration accounts for 25-40% of cooling demands in summer.
Ventilation
Ventilation replaces indoor air with fresh outdoor air. This dilution of warm indoor air can have a cooling effect. At night, open windows bring in cooler outdoor air which absorbs heat from indoor surfaces.
Should Windows Be Closed During the Day?
Here are some pros and cons of keeping windows closed during the day:
Pros
- Prevents solar heat gain from sun shining through windows
- Stops warm outdoor air from infiltrating and raising indoor temps
- Traps cooler air inside the home
- Reduces load on air conditioning
Cons
- Can cause a pressure imbalance leading to stuffiness
- Prevents ventilation and air exchange
- May trap odors, moisture and pollutants
- Eliminates fresh outdoor air
Overall, keeping windows closed during the hottest times of the day in summer will help block solar heat gain and keep indoor temperatures lower. Late afternoon or overnight are better times to open windows for ventilation.
Should Windows Be Closed at Night?
Here are some pros and cons of keeping windows closed at night:
Pros
- Prevents warm outdoor air from raising indoor temperatures
- Keeps cooled indoor air from escaping
- Reduces pollen, dust and outdoor allergens from entering home
- Provides added security
Cons
- Traps stale indoor air and prevents night flushing
- Inhibits ventilation and moisture control
- Can cause stuffiness and odors
- Misses out on cool nighttime breezes
In most climates, it is beneficial to open windows at night to flush out built-up heat from the day. This allows cool outdoor air to enter and absorb heat from indoor surfaces. Just be sure to close windows in the morning before temperatures rise again.
What Factors Impact the Effectiveness of Closing Windows?
Several variables impact how much closing windows helps reduce indoor temperatures:
Outdoor Temperature
Closing windows is most effective when outdoor air is hotter than desired indoor temps. During cooler weather, ventilation from open windows may aid cooling.
Indoor vs Outdoor Humidity
If outdoor air is more humid than indoor air, infiltrating air could increase mugginess. Keeping windows closed will prevent added moisture.
Window Type
Well-insulated, double or triple pane windows with low-emissivity coatings provide more insulation when closed. Old single pane windows transfer more heat.
Window Coverings
Closed blinds and curtains boost window insulation. Open curtains allow more heat through windows.
Shading
External shading from trees, overhangs or awnings blocks solar heat gain through closed windows. Unshaded windows receive maximal sunlight.
House Tightness
Well-sealed homes will better retain cooled indoor air when windows are shut. Drafty houses allow more air infiltration.
Other Ways to Keep a House Cool
Along with strategic window use, some other ways to keep a house cool in summer include:
External Shading
Install overhangs, awnings, exterior blinds and plant trees to block solar heat gain before it enters windows.
Window Coverings
Close blinds, drapes and curtains on hot sunny days to reflect heat away from windows.
Attic Ventilation
Ventilated attics allow hot air to escape, reducing heat transfer into living spaces.
Radiant Barriers
Radiant barriers like foil-faced insulation installed in attics reflect solar heat gain.
Landscaping
Shady trees and plants around the home provide passive cooling through evaporative effects.
Fans
Circulating fans move air to create a wind chill effect, cooling people through convection and evaporation.
Ventilation
Strategic window and door opening creates cross breezes for ventilation and heat removal.
Air Conditioning
AC actively cools and dehumidifies indoor air for lower temps. Closed windows help retain this cool air.
Home Insulation
Adequate insulation slows heat transfer into the home through walls, ceilings, floors and foundations.
Conclusion
Generally, keeping windows closed during the hottest parts of summer days helps reduce solar heat gain and infiltration of muggy outdoor air. This can maintain lower indoor temps. However, allowing windows open at night enables beneficial ventilation and air exchange that purges built-up heat. Strategic window operation along with solar control, ventilation, fans, and AC if needed, provide whole-house cooling. Consider your local climate and home features to find the ideal window positions for staying cool.
| Time of Day | Recommendation | Reason |
|---|---|---|
| Morning | Keep windows closed | Prevent early solar heat gain as temperatures rise |
| Midday | Keep windows closed | Block peak solar heat gain |
| Afternoon | Keep windows closed | Continue preventing heat gain as daytime temps peak |
| Evening | Open windows | Allow ventilation to flush heat buildup from day |
| Night | Keep windows open | Maximize cooling night air intake and ventilation |
| Early Morning | Close windows | Retain cooled air before heating up again |
Strategic window operation, external solar control, ventilation, fans, AC, and quality insulation work together to keep a house maximally cool. Consider your local climate, housing design and lifestyle patterns to find your ideal window positions. Monitor conditions inside and outside your home to adapt as outdoor temperatures fluctuate during changing seasons and times of day. With the right window use and home improvements, you can beat the heat without wasting energy.
Frequently Asked Questions
Should I close my windows during a heat wave?
Yes, keeping windows closed is recommended during hot summer days, especially heat waves. This reduces heat gain from sunlight, hot outdoor air infiltration and conduction. Close blinds and curtains too.
Is it bad to sleep with the windows open in summer?
It’s usually fine to open windows at night to flush out built-up indoor heat. Just close them in the morning before temperatures climb again. Use screens to prevent insects.
What happens if you keep windows closed all day?
Keeping windows closed all day traps hot air, odors, moisture and pollutants inside a home. It is beneficial to allow nighttime ventilation by opening windows in the evening.
Should you close windows when running AC?
Yes, keeping windows closed allows air conditioners to work more efficiently. Leaving windows open forces the AC to continuously cool the infiltrating hot outdoor air.
Is it better to close windows at night in the summer or winter?
In summer, windows can be open at night to flush warm indoor air and increase ventilation. In winter nights, keep windows closed to retain indoor heat and prevent cold outdoor air from lowering the temperature.
Key Takeaways
- Closing windows during hot summer days reduces solar heat gain and warm air infiltration.
- Opening windows at night enables ventilation to flush out built-up indoor heat.
- Outdoor temperature, humidity, window types, window coverings and house tightness impact window closing effectiveness.
- Use fans, ventilation, window coverings, landscaping and AC along with proper window use to maximize summer cooling.
- Consider climate, conditions and lifestyle to find your ideal window schedule for staying cool.