Nearly any vinyl window can be manufactured to fit a custom size opening. I'm not familiar with the Newcastle per se but Certainteed Windows are made by MI which, while they don't produce horrible windows, also don't have a reputation for producing the best. I would encourage you to look at some other manufacturers so that you can get a feel for what constitutes a quality window. Do not assume that because 2 windows have the same energy efficiency numbers, that they are of equal quality.

Follow-up***

I just remembered that the NewCastleIII is the old Bren MawrII. It a low mid-grade window built for the budget shopper. It that fits your profile, you should be OK as long as you don't overpay for it. However, keep in mind it is a budget window, similar to buying furniture from Walmart.

Skydawggy, thanks for your reply. I was wondering if I might send you an email to ask you a couple of questions, since you seem pretty knowlegeable about windows??

I've gotten so many different answers from the contractors and salespeople where I live regarding windows, that I'm not sure of anything anymore! I'm ready to just scrap this window project soon if I can't get some answers to some important questions!

Cassie

It can be pretty frustrating. Sometimes I spend more time convincing someone that what they were told simply isn't true or that it's just sales hype than I do enlightening them to the realities of purchasing windows. Just click on my email and I'll be happy to try and help you sort it out. Or you can visit my website and send me an email from there.

Here is a link that might be useful: EcoStar Remodeling