Windows, Doors, & Envelopes: How They Impact Your A/C Unit

San Antonio’s heat wave is already setting records and taxing the energy grid, making it more important than ever for homeowners to ensure their A/C units are operating at maximum efficiency. One major culprit of an inefficient A/C unit is a leaky building envelope. In this article, we’ll explain how you can examine your building envelope, specifically windows and doors, and provide some improvements you can make to them to help keep your A/C unit running efficiently all summer long.

What is a Tight (or Leaky) Building Envelope?

As your A/C unit runs, it draws air in and pumps conditioned air into your home. When air is drawn in, your system pulls air from anywhere possible—doors, windows, floor or ceiling registers, light switches, attics, and other areas where gaps in walls occur that can allow air to “leak”. Air leaks can make it difficult to maintain the desired inside temperature and force your A/C unit to work harder than normal.

When a new home is built, it’s required to undergo an energy audit that tests how tight the building envelope is, or how much air infiltrates the home. Since energy efficiency wasn’t a primary concern in the past, older homes tend to have leakier building envelopes. Regardless of the age of your home, examining the tightness of your building envelope can give you the information you need to make any necessary improvements to your building envelope to ensure A/C unit efficiency.

What Problems Do Windows and Doors Pose?

Unlike walls, windows and doors are a unique part of your building envelope as they may let light in or be opened. When properly installed and maintained, they can improve a home’s energy use. However, over time, or when installed improperly, they can cause your A/C unit to perform inefficiently.


There are two primary ways windows can cause your A/C unit to be inefficient: broken seals and radiant heat.

1. Seals

Single-pane windows have plastic glazing strips that seal the glass to the window frame which, with age and exposure to the elements, can corrode and allow air to flow freely around the glass. This is called air infiltration. If you feel air coming into your home around the window while your unit is running, this is likely the culprit. It is well worth it to replace these types of seals and it can easily be done on your own.

Double- and triple-pane windows are more energy efficient as they have more seals but, when these seals go bad, they can cause both fogging between panes and air infiltration. Repairing this type of issue may require professional help.

2. Radiant Heat

Because of their energy efficiency, by replacing single-pane windows with double- or triple-pane ones, you can make a tremendous difference in the amount of radiant heat that enters the home. New windows are an investment and will pay for themselves over time. Be sure to let the HVAC professionals know if you replace your windows because it plays a big factor in assessing your system.

If new windows aren’t in the budget, you can take steps to reduce radiant heat by installing efficient window treatments, like blackout shades, or reflective tint that directs sunlight away from the windows. 


Doors are made up of a variety of materials. Any doors with glass are like windows and can suffer the same seal-rot and air infiltration problems as explained above. While some doors are better insulated than others based on the material they’re made of, weather stripping makes a far greater difference in your home’s efficiency. 

The weather stripping around the rest of the door can easily corrode, rot, or become damaged by animals, children, or general rough treatment. In some cases, weather stripping is defective from improper installation. Remember—if you can see light around your door when it’s closed, this means that air can enter the home from outside. It’s worth checking your door’s weather stripping at least once a year to ensure it’s still in good shape, and it can easily be replaced if you notice there’s an issue.


Because windows and doors are integral components to your building envelope and can heavily impact your A/C unit’s efficiency, it’s important to look for and fix air leaks in your home. If you’d like to assess your home’s air infiltration or evaluate the health of your A/C unit, contact North East Air Conditioning, Heating and Plumbing. Our experienced technicians can help identify problem spots in your home and ensure that your A/C unit is working to its potential.

Photo by Gia Oris on Unsplash


Call: 210-658-0111