Is it Bad to Leave the Windows Open When the AC is On?

South End Plumbing, Heating, & Air Expert Tips

Running the AC and having the windows open at the same time generally isn’t a good idea. In short, it’s a waste of the air conditioning and can impact the air quality inside a home. Opening windows defeats how an air conditioning or HVAC system functions. When windows are open, the airflow of the system won’t work as it’s designed. Air escapes and untreated air – both for temperature and cleanliness – comes in.

What’s the AC Doing Because the Windows Are Open?

The AC Works Harder

With open windows, most of the air coming out of the AC into the home is exiting the home. The design of an HVAC system is to have a circulating air flow. Now, you’ll probably have to readjust the AC to get it to a cooler temperature. You could believe the air is cooler outside, but this is often deceptive. Ultimately, your AC unit will be inefficient, then could even fail, due to nonstop use. Even in the short term, running the AC more than it needs to leads to higher electric bills.

Wear and Tear

The air from outside brings dust and higher humidity into the house. These additions, especially at very high levels, can wear and damage parts of the system, even a thermostat. Layers of dust and particulates can gather and be a problem for thermostats, filters and other HVAC parts. Plus, you and your family are breathing more of the dust, pollen and humidity in.

The AC system will have to work more on cooling and filtering or treating the air, which isn’t entering the system as it’s designed for. By putting all this added work on the HVAC system, expect your utility bills to be a lot higher. Some might say the added cost is worth it. They may not understand how substantial those costs could end up, though. The more stress on an AC, the worse it functions and has parts break. You end up with more repairs at some point. You maybe even reach the point of the worn parts or components not being cost-effective to fix.

Air Quality

When you leave the window open, not only does air escape from your house, dirty air comes in. This means you and your family are breathing in unclean air that is being recirculated in your home by the air conditioner. The resulting dust can additionally hurt your cooling and heating system by coating its components and coils and hampering the system from working as it’s built to.

Unexpected Issues

It’s possible a sudden, surprise rain – which never happens on hot days in the Carolinas – could cause a sudden mess just inside an open window.

Leaving windows open may clog filters. Now, you’ll need to change them more frequently, if you remember to change them at all. An old, clogged filter will work less effectively than it’s supposed to and a very dirty filter can actually make a home and the air dirtier with more problems than no filter at all.

Dirt and other particulates in the air can create failures and more expenses. Dirt can cover the evaporator coil which then slows air cooling. Old or filthy filters decrease the airflow through the air handler, which forces the air conditioner to run longer. An evaporator coil can even freeze and ice over. This can cause a blown compressor, and a huge headache for you.

Better Ideas Than Opening Windows

What are some better ideas rather than opening windows and running the AC, especially overnight?

Since it cools off a bit in the evening and night, you might want to open a window. You might think it’s saving a little money. This usually isn’t the case. There may be factors and side effects you wouldn’t know or expect. Evening air is generally more humid, so the higher moisture is coming in. This changes how the house feels. It changes how the HVAC system has to run. An HVAC’s airflow is mostly trying to take moisture out of the air.

Using Curtains or Blinds

When you see the sunlight coming in, it is making a room or area of a house hotter by the minute. You can put up, then remember to use, curtains and blinds. Keeping your rooms shaded keeps them cooler. In hot areas, this may not make much of a distinction. It functions by decreasing the sunlight from heating the inside of the house.

Tinted Windows

Tinting home windows can be a good idea alongside curtains or blinds. If you have tinted windows and curtains, they can go a long way in helping you keeper cooler temperatures in some rooms or areas of a house.


There is an unlimited choice of material you can utilize to protect your walls, floors and roof covering. Insulating may cost money up front, but it is a long-term solution with multiple benefits. Insulation works by preventing heat from entering a structure while preventing cool air from escaping the house. With proper insulation throughout a house, the air conditioning system reaches the temperature you’ve set more efficiently.

The Right Temperature

What temperature is the right setting, even on the hottest days? Personal preference is always different here, but 78 degrees is typically the balanced and efficient setting for an AC during the summer. You should be able to change it 2-3 degrees either way with very little difference in cost and function. It is effective in cooling the air, as well as using power efficiently. Just remember it’s best, nearly all the time, to keep the windows closed.


At South End Heating and Air we are Charlotte’s affordable AC experts. Call us anytime for a free consult and free estimate. We’ll evaluate your system and help make recommendations for optimum value. After all, we want to keep you cool all summer long and warm in the winter. Just schedule a visit with one of our technicians to talk about how we can help. Would you like to learn more options our techs can help you with? Give us a call 704-684-5339.

South End Plumbing, Heating, & Air Expert Tips

We're ready to help with all your needs!

Book Online Book Online