What is the benefit of an added internal metal frame/core on vinyl windows?

We are about to replace our 1965, single pane, full metal jacket, rattle-when-a-helicopter-flies-by windows. Since we want to get rid of the metal frame and trim we need to do a full replacement of the entire window, including the frame.

We have received quotes for windows where the frame is made entirely of only vinyl; a cut-away of such a frame is shown below:

Vinyl Window Frame

Another (more expensive) quote had windows that included an internal metal frame, sample shown below:

enter image description here

I have been cautioned against windows that are vinyl-only as they may be more susceptible to thermal expansion and contraction, especially since we are in Southern California. Additionally, above a certain size, vinyl-only windows supposedly are more prone to having the frame sag over time.

We do not live in a "fancy" neighborhood, so vinyl windows are appropriate. However, I wonder whether going with a high-quality vinyl-only window is sufficient or whether a metal frame is more desirable for long-term survivability of the investment?

  • Those "benefits" sound like they were provided by the manufacturer of the windows with the metal inserts. I'd say the same thing about the cutaway views. The all vinyl cutaway is not what the cross section of a normal vinyl window looks like. Also, the metal has far more thermal expansion and contraction than the vinyl, and I've never seen a vinyl window sag (and I had a huge picture window). If that's the source of your information, it sounds like a con job and I wouldn't trust the company. – fixer1234 Apr 28 '18 at 4:00
  • See if any neighbors replaced their windows with vinyl years ago. See what condition they are in, and ask the homeowner what they are. – fixer1234 Apr 28 '18 at 4:10
  • @fixer1234: Cutaway is from the actual brochure they left at our place; brand is Monte Verde by Anlin. I am still puzzled by why some manufacturers would choose to add metal to the frame - seems like a pretty dramatic design decision if it is not necessary... – nodapic Apr 29 '18 at 23:33
  • It's not a question of "necessary". It's something they can do cheaply just to be different, then convince people to pay a lot more than the incremental cost because it's "better". I would expect a metal channel in that location to shorting the window life rather than lengthen it. – fixer1234 Apr 30 '18 at 0:27

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