Should not be a problem if they are individual windows mulled together and use a mainframe. If it has a nail fin that wiuld have to be addressed.

Very carefully

I assume that this is a twin double hung?

The degree of difficulty in separating will be determined by what type(make and material) of window it is, and how they are mulled. Could range from pretty easy to nearly impossible without damage. Are they vinyl? Wood?

Secondly, if the unit was measured for the existing mull post to be removed (I presume), then separating them would likely still end up with two windows that are too wide for the individual openings.

Lastly, is it certain that the existing mull post is structural? Do you have a picture?

Wood? Vinyl? Aluminum Clad? Fiberglass? How were the windows mulled in the factory? If wood is there a continuous one piece sill? Maybe post up a picture or two.

It is a fiberglass window - Anderson 100 series to be exact. Not sure how they are mulled. My window order simply states “factory mulled”.

Existing post is structural. It has a beam running over it.

It is a fiberglass window

Andersen 100 series is not fiberglass.

Ok my bad. It’s Anderson 100. For sure. And you are right it’s some sort of composite material that I was confusing for fiberglass. Anyway. I hope it clarifies the question now.

Check with your contractor if the existing windows are separated by the post, most of the time they will cut one header to cover the span of the opening if window separation is 1-3 2X's, if that is the case the post can be removed and you can use a mulled factory window by adjusting the opening.

That said, in some cases, Anderson windows can be mulled in the field they come with a mull joining and trim stips you can carefully take them apart and all you have to do is add nailing fins.

But before you do that, contact Anderson service department to make sure the window you got can be disassembled because at times factory-mulled windows cannot be taken apart.

Good luck

GN Builders advice above is spot on.

ABC, to my layman eyes it looks like one piece therefore a single window. However the description says it’s a factory mulled window. Contractor thinks he can try to un mull it.
To answer other questions — the post is for sure structural, if the window is to be used as is then there will be a load bearing beam needed and that will trigger a number of other changes that we do not wish to pursue.

Thank you for the information. I’ll check with Anderson.

Btw - for what it’s worth, it’s got two middle panes that are fixed and the two side panes are casement style. The mulling seems to be between the two fixed panes.

Homey_bird, what I was trying to point out to you is, in most cases when you have a side-by-side window separated by a post like it shown in the image. Post is not a bearing component it is only used to separate the window and have some surface to put the siding, etc in between.

But if you have something like this and the post separating the 2 headers (which I have never seen anyone framing this way not to mention it makes no sense just a waste of time and lumber)

in this case good luck with taking that window apart.

Design wise, traditional double-hung windows have counter-weights that occupy space beside each window. Most present day double-hung do not have counter-weights and the space beside each window is not required. If it is desired for the house to have a traditional look, space should be provided on each side of a double-hung window to at least give the appearance of a true traditional double-hung window. Windows mulled together in the factory normally do not provide the space or the appearance of the space for the counter-weights.

(just a little design tip)

She has casements @Mark Bischak, Architect.

Ok, so overall everyone is leaning in the direction of "not possible/not easy". Thank you, let me open the packaging and if there are any questions, then I would post with pictures.

Thank you everyone!! This is helpful.

@homey_bird, before you start tearing anything apart, as I alluded to earlier, check the measurements. If this unit was measured correctly to be installed as one, mulled unit, then separating these windows will result in units that are too wide to be installed in those individual openings anyway. I would say that Andersen 100's have a fairly decent chance of being able to be separated without issue, but again, they may not fit anyway.

Also, not to belabour the point, but @GN Builders L.L.C gave some nice illustrations of what I also mentioned above, which is that the presence of a mull post under a header or beam doesn't automatically mean that it is structral, and in fact it often is not. The only time I generally see that (IE: the second illustration posted by GN) is on very wide openings where a taller header would be needed to span the width without breaking up the opening.

Do you have photos of the opening in question? That would help.

Plenty of info on the Andersen website.

Frustrating, and especially with the delays involved…but to preserve the warranty, I would bite the bullet and order the correct windows. Whoever made the initial mistake should be forgoing at least their markup…
Donate the surplus windows to someone like Habitat for Humanity, and claim the deduction.