Have you looked at indow window inserts? That is exactly what they do (theirs are acrylic)

Great input. I am concerned about condensation... we do get some on the double paned glass. The Indows that Hallet & Co mentioned are supposed to help address that - so I figured that a second set of double/triple pane windows would make that a non-issue. As for storage and handling - at least for the fixed windows - I would assume this would be a permanent installation. I was thinking something more like the Indows for the casements.

Oh - re: drapes - we have gone that route for the regular windows ... but the great room is not conducive to them... see below

I live in Hardiness Zone 5 (Michigan).. here's my review after 2 years of having the EnergySvr Window Inserts from windowinserts.com . Reality is, if you have NOT owned them, you don't know. I was skeptical at first.. but 2 years later..

This is my review for Window Inserts. This review is being provided as my own, I was not given any special pricing, free product, or any other incentives for providing it.

** Short Version – I WHOLEHEARTEDLY RECOMMEND THESE WINDOWS AND COMPANY **

I originally purchased my window inserts in 2019 for use in a rebuilt 3 season room. The room itself has 6 openings, all of different sizes. There are NO traditional windows in the room, and the only “window treatment” is the old style framed screens that I built myself. I spent a LOT of time looking for a way to close the openings off at the best price and easiest way for me to do them. I am a disabled veteran with severe back issues, the 3 season room holds my hot tub, so condensation and heat transfer where a big concern with this project. I spoke with at least 3 or 4 other places, and received quotes for the “inserts” ranging anywhere from 3 to 12 times as much as the quote from Window Inserts. The two big cost reasons where the types of material used, and that the openings where irregular sized. Two of them actually have top and bottom widths that are different from their opposing ends, by as little as 1/8”.

Upon my first call, the owner of the company took my call, answered all of my questions, and gave me an estimated price for the windows, which may have gone up or down depending on shipping costs and final opening sizes. Again, this quote was vastly lower than any other “insert” style manufacturer I was able to find. One of these reasons, is the material that Window Inserts uses to make the transparent part of the window itself. The owner assured me that the material was durable enough, and would provide good protection from the Michigan winter cold and winds. The windows are rated for a sustained 30mph wind, or gusts up to 40. For us in Michigan, that’s a typical winter Tuesday. So, I placed the order since the price was, frankly, too good NOT to place an order, and the service was AMAZING. I think we did 2 or 3 size checks because *I* wanted to make sure they where right on my end. The windows, if your ordering multiple, come numbered so that you will always get the right insert into the right window. Also, the company keeps your order in their computer, so if you need to reorder just one window, they can pull up the order and sizes from the system, and save a bunch of time. The windows do have a warranty, and the company definitely stands behind it. I received the windows about 10 days after ordering them, and was floored. The transparent material was SOOO thin I didn’t see or think it was going to hold up, let alone help with any type of heat loss. Well, 2 pretty harsh and windy Michigan Winters later, and I can tell you without hesitation that they not only perform, they held up so much better than I ever expected. High winds.. check. Rain.. check.. Blizzard.. check. I even wanted to test to see exactly how much they made a difference so I got an external digital thermometer. The average heat retention in the 3 season room is between 22 and 32 degrees WARMER than it is outside. That is with the hot tub CLOSED and no extra heat from any other sources. With the hot tub open, the 3 season room routinely breaks 80 degrees in the dead of winter. Remember, there’s NO GLASS in my 3 season room.. it’s mother nature, a screen window, and then Window Inserts. During our winters, we routinely get 30+ mph winds, and these window inserts have held up in their open 51” x 55” frames without fail. 40+ mph.. they still hold.. 50+, yup.. still holding. It took a 62mph gust to blow ONE of the six windows in. The other 5 remained in place without any sort of modification or additional holding devices, materials, etc. In the winter months, the outside frame of the window is sealed with foam insulation. This foam flexes to fit your openings, and I’ve found that when it’s freezing outside, it causes that foam to freeze in place. That thin little layer of ice actually holds the windows in when it get’s overly windy outside. When it thaws out, the foam absorbs the water and then dries naturally, so you also don’t get any running water over the sills nor any odd smells. I would not expect this “foam freeze” if you put them inside of your house windows.

As far as the warranty goes.. well.. on this one I failed a bit. I forgot that they do infact cover the foam, and if you need replacement foam, you simply call them and they’ll send you some for free to replace any damaged foam. These windows are incredibly light, my initial package weighed less than 20# for all 6 windows. The frames and corners have NEVER failed me, and the only damage that was done was after I dropped a window and bent the frame on the edge of my hot tub. This was actually a fluke, and totally my fault. The owner of the company was quick to answer the call and gave me a great deal on a replacement window, including making it, and another, in their new divided style, which I’m looking forward to putting in. Even with the recent issues in shipping and manufacturing, this order was just as fast, and I received my new window inserts in 8 days from my order. 8 Calendar Days.. not business days.

In an age when customer service, honest pricing, warranty coverage, and an amazing product are getting harder to find, almost by the day, Window Inserts ticks the boxes on all four. The product is absolutely amazing in my opinion, and I HIGHLY RECOMMEND them to anyone looking for an insert to help retain heat in your house or 3 season room.

I am so excited to read your thourough review! This is just the product I have been looking for. We are building a screened in porch. I was thinking of using E-Z breeze four track windows, but they won't work well for our application! This will be much better. Website is easy to use. Looking forward to starting my project now that I finally found the right solution!

I hope they work out great for you. Remember.. the data I presented was my own, and not anything that the company guarantee's or even promotes. It's going to be different based on your area and conditions. This third year, just as an added precaution, I added metal pegs to the 4x4 studs to assist with holding the windows in, since we where expecting (and got) some crazy strong winds over the winter months. Only one window needed the pegs, and then only once, but it was a better safe than sorry addition. Best of luck with your new windows!