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Window Mullions and Muntins – What’s the Difference

When we think about the parts that make up our windows, we usually think about panes of glass, sills, frames and casings. While you may not have heard about mullions and muntins, it is quite possible that you probably already have them on your windows or even your patio doors without even realizing it. So, what are muntins and mullions?

Window Mullions and Muntins - What’s the Difference

Window Mullions

Window mullions are the vertical bars that divide two or more panes of glass in a window. Although their main purpose is to provide rigid support, they can also serve as a decorative element. Prior to the Victorian era, it was not possible to manufacture large sheets of glass, so large expanses of windows were achieved by providing them with support via the use of mullions.

Window Muntins

Window muntins, on the other hand, are sash bars made of wood or metal strips that separate and support the glass panes in a window. Muntins only refer to the inner vertical pieces. While they are most associated with windows, they can also mean any kind of vertical divider used for doors, wood panels and even furniture.

To put it simply, muntins are inner, vertical elements that separate panes of glass in a multi-pane window while mullions are single vertical supports used in multi-pane assemblies. Not many window companies make a distinction between muntins and millions because few homeowners care about this, and, oftentimes, they are used interchangeably. A more buyer-friendly term that window manufacturers use is grille.

Whether it’s French doors or your traditional casement window, you will probably see these elements in most houses in your neighborhood. If this is something you care about when looking for windows to purchase, give Renewal by Andersen® of St. Louis a call (314) 332-2364, or fill out our contact form to speak to one of our window experts.

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"I'm getting ready to do my 2nd round of window installation with Anderson Windows. I really appreciate the great financing options that they offer! They have top notch sales and installation experts who are very kind and considerate of their customers' wishes. The windows I have installed look great and I am so excited to get the next group of windows put in. My house looks so much brighter with my new windows. I definitely recommend Renewal by Andersen of St. Louis."

Connie Klinginsmith-Rehfeld
Feb 2, 2024

"We recently contracted with Renewal by Andersen to replace 5 windows in our home. First of all, we were very delighted that the time from contract to installation was less than two months. Joel and Craig arrived precisely at the agreed-upon time and spent less than four hours from start to completion of installation, including time to demonstrate opening/closing the windows and any questions we had. We were very pleased with the knowledge and professionalism of Joel and Craig, and, of course, we’re very pleased with the windows and how nice they look. We definitely recommend Renewal by Andersen."

Marla Merenghi
Feb 1, 2024

"I replaced my front door and several windows. The install team did a great job with installation and clean up. Even covered floors and stairs. The team was very courteous and did a very professional job. Now our windows look great and we love our new door. I would recommend Renewal by Anderson in a heartbeat."

Rose Brown
Jan 25, 2024

"From the sales person to the installers this was a very professional and personable experience. The installers were extremely hardworking and great at their job! Customer Service was excellent and responsive to each question. My salesperson stayed in touch throughout the entire process as well. I’m very happy I chose this company!"

Gailynn Campbell
Sep 20, 2024

"We had a wonderful experience with Renewal by Anderson of St. Louis. From sales to office staff communication to installation everything was great. Our new windows are great quality, look amazing and improved the overall look of our house. We had four installed in August and will definitely be purchasing from Anderson for the rest of our windows in the future. I highly recommend! ❤️ Now it just needs to cool off outside so I can open them. 😃"

Monica Balestreri
Sep 19, 2024

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