...
Since the OP's house is new, he almost certainly has double-pane windows. First of all, if his windows are decent at all, they'll already have a low-emission coating on them. Second, applying window tint to them would void the warranty. (And that warranty is important, because double-pane windows do tend to fail. Knowing what I know now, if my house had traditional single-pane windows I'd be inclined to keep i that way despite the alleged efficiency of double-pane ...)
Can you elaborate on this? You imply there is a secondary down side to modern windows after the upfront cost. Or would you just prefer tinted windows? Or the failure rate was high in your case and not worth the hassle?
There is a downside from my view: You can maintain old single pane windows to last for 200+ years. Show me a modern window that will last that long. If the seals haven't failed, often some other proprietary hardware has. Vinyl parts that age and get brittle, plastic parts that snap/break after 20 years, and you can't get replacements because the company went out of business years ago, etc. Now, in a house built in 1990 with vinyl siding and failing windows, I can't just remove the window. Since there's integral mounting flanges, the siding must be removed around it, etc.
Studies have been done comparing the efficiency of replacement dual pane windows vs old single pane, and the payoff is often not worth the investment. A well-maintained single pane window with a storm window over it isn't as energy inefficient as you'd think compared to a typical dual pane modern window.
You'll notice VERY few new window manufacturers will give you an air infiltration number. You'll get U-value / R Value, light transmittance, but not air infilt. Why? Because most of them aren't that great at it.
So, the modern windows ARE better energy-wise when put in as new. But, you have to be careful when you're looking at lifetime cost. Old-style windows will need some maintenance, but complete replacement being necessary would then be quite rare. Newer windows seem to be MUCH more hit and miss. You may save on energy, but lifetime cost goes way up when you have to replace the entire window in 10-30 years.