I always choose new construction over retrofit because the window is less likely to leak, I prefer the overall look, and I don't lose any of the glass area. Remember that when retro is used you'll lose a certain amount of view out the window. Both retro and construction can be purchased in any size since any window is consider 'custom'. There's nothing worse than a window or patio door that doesn't slide easily, so keep looking until you're happy with the product. I'm not familiar with Brother's brand but Milgard has a good reputation here, as does Pella. New construction may cost a little more if you have a stucco home so research the total cost based on the exterior of your home and whether the trim can be re-used.

JaneSylvia, I'm no window/door expert but my DH and I have some experience. I'm only familiar with Argon gas in Andersen windows. Its heavier than air and has a higher R-value than regular air. Our first dual pane windows were made in 1975 by International (no longer in business). The seals broke on them within 10 years and were so bad you could hardly see through them. Whatever you do, make sure they have at least a 20-yr guarantee against glass failure. You absolutely want LOW-E glass. Having had both regular dual pane and Low-E (Andersen casement) there is no comparison between the two. Plain dual-pane doesn't do much for keeping the heat out in summer. My DH replaced windows and 2 patio doors in a rental house with Jeldwen from Home Depot. Retro is much easier if you're doing the install, but it does reduce the visible glass so it makes your window smaller. Of course, its only as secure as your original frame when the house was built. The Jeldwen from HD are all vinyl and we did have a bad experience with them. My husband accidently hit his boot against the frame of the patio door and a 7" long piece of vinyl broke off. To our amazement the piece was hollow, not solid vinyl. Jeldwen would not replace the door even though it was brand new. Said it was our fault. We think its a design flaw. If you're going to stay in your home and can afford it, I would recommend Andersen. They make a retro window but we've only had experience with their new construction 400 series casement windows and their 12' Frenchwood Glider (it looks like a French door and not a patio door, i.e., 9" bottom wood rail). I also love their screens. They have strong mesh (not the normal fiberglass cloth) and you'll love the way they easily clip in and out for cleaning (we have casement windows). If you want to learn more about dual pane windows, check out my post "Andersen glass failure due to negative pressure". I still think they make a great product! Good luck with your project.

Wow- you really dislike Pella, I take it. Since the lawsuit, I wonder if Pella has changed their windows, and maybe opinions of them would change- or do you think the quality continues to be horrible? My brother got them on his new build- they 'look nice' - but who knows what will happen in 5 years. I have Andersen casements now, and they are OK after 25 years (wood exterior and interior starting to rot out now). Regarding Andersen-and mixing- Do the quality reviews on 200s vs. 400s carry down to patio doors? Meaning, are the Andersen 200 French and Sliding doors 'just as crappy' as the Andersen 200 windows, in your opinion? If I'm trying to stay on budget with Andersen, where does it make sense to splurge for the 400s (say for all 27 double hungs) and go with the 200s for the 2 patio doors, 2 large Fixed windows, 1 casement, 1 smaller fixed window)?

We have been replacing windows over the past two years and have had our local glass replacement business, which does windows and glass shower door installations, do the work. The second floor windows were done by a different installer who took too long and was a one-man operation. Each installer, we found, used windows manufactured by small operations -- one in Minnesota and one in Ohio. We've found that most replacement windows were manufactured the same way and looked very similar. The important factor was the installer, his/her skill, and knowledge about what they were doing. Our installer even replaced some interior trim in the kitchen. We removed the old wood windows which were original to our 1928 home with vinyl. Very happy with the results. So my point is to check with your local business and they will tell you who they use, give you an estimate, and references. Good luck!