I am in the process of getting Okna 500 windows installed to replace old wood windows in my house. One of the companies told us that for the two or three double hungs that are next to each other, they can do "factory mulls", which might be cheaper than two or three standalone windows and also may be better structurally. I asked that to another company and they said no, they can't do that, as the combined width can't exceed 52 inch or so. My question to the forum is whether or not I should ask for factory mulls. Thank you all in advance.