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.
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 parts break. You end up with more repairs at some point. You may even reach the point of the worn parts or components not being cost-effective to fix.
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.
It’s possible a sudden, surprise rain 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.