Written by Big Easy Windows
Key Takeaways
- The NFRC label on a new window reports U-Factor, Solar Heat Gain Coefficient, Visible Transmittance, and sometimes Air Leakage. Lower is better for the first two.
- In New Orleans, SHGC does more work than U-Factor. Our problem is keeping solar heat out, not keeping furnace heat in.
- Orientation changes the right answer. West-facing glass takes the worst afternoon load in this climate.
- Ratings describe the window as tested. A poorly installed high-performance window underperforms a well-installed average one.
- Big Easy Windows walks through label numbers on every quote. Call (504) 384-8165.
The Number Most People Read First Is the Wrong One
Quick Answer: Homeowners tend to fixate on U-Factor because it’s listed first and because national marketing emphasizes it. U-Factor measures heat conduction, which matters most where winters are long and cold. In the New Orleans metro our energy load is dominated by cooling, so Solar Heat Gain Coefficient, the fraction of solar radiation that gets through the glass, is the number that actually moves your bill.
Both matter. In our climate, SHGC matters more.
What Each Number Means
U-Factor
How readily heat moves through the window assembly. Lower is better, and residential values generally run in a range around 0.20 to 0.60. It counts here for keeping conditioned air where it belongs, just not as much as it counts in a cold climate.
Solar Heat Gain Coefficient (SHGC)
The fraction of solar heat that passes through, from 0 to 1. Lower means less heat entering. This is the Gulf South’s headline number. Low-E coatings are the main tool for pushing it down, and they’re the reason two windows that look identical can perform very differently.
Visible Transmittance (VT)
How much visible light comes through. Higher means brighter. The tension is obvious: aggressive solar control can darken a room. Modern spectrally selective coatings are designed to reject heat while passing light, which is exactly the tradeoff you want here.
Air Leakage (AL)
Air passing through the assembly. Lower is better. In our humidity, air leakage also carries moisture, so it’s not purely an energy question.
Choosing by Orientation
Different elevations of the same house have different problems.
- West-facing: the hardest exposure here. Low afternoon sun drives straight into the glass during the hottest hours. Prioritize low SHGC.
- South-facing: heavy sun through much of the day. Low SHGC again.
- East-facing: morning gain, generally easier to live with.
- North-facing: the least solar load. You can favor higher VT for daylight.
Specifying one glass package for the whole house is simpler and often fine. If budget forces prioritization, spend it on west and south. Shading helps too, and exterior solar screens are a lower-cost way to cut gain on problem elevations without touching the glass. Awnings and storm window options can play a similar role depending on the opening.
Where Ratings Stop and Reality Starts
A rating describes a window tested in a lab. Your comfort depends on that window installed in your wall. Gaps behind the frame, missing flashing, or an unsealed rough opening will undo the performance you paid for and, in this climate, invite moisture problems on top of it.
That’s why we treat the install detail as part of the spec, not an afterthought. Our window installation process walks through what happens at the opening, and choosing a window installer covers what to ask when comparing bids.
Frames Matter Too
The label rates the whole assembly, so frame material is baked into the number. Vinyl performs well thermally and holds up in humidity, which is a large part of why it dominates replacement work here. Our window frame materials guide compares the options, and wood vs vinyl goes deeper on that specific pairing.
Does Better Glass Pay for Itself?
Payback depends on your current windows, your rates, how you run your system, and your home’s shading. The honest framing is that the upgrade from single-pane or failed older units to modern low-E glass is a large step, and the step from good to slightly better is a smaller one. Comfort is part of the return too, and it’s the part homeowners notice first: less radiant heat off the glass, fewer hot spots in west rooms.
Our post on energy efficient windows and cooling bills covers what to realistically expect.
Frequently Asked Questions
What SHGC should I look for in New Orleans?
Lower is generally better for our cooling-dominated climate, particularly on west and south glass. Ask for the actual rated numbers on the specific package being quoted rather than a general claim of energy efficiency.
Is triple pane worth it here?
Triple glazing mainly targets conductive heat loss, which is a cold-climate priority. In this climate, spending on solar control and installation quality usually returns more than adding a third pane.
Do all new windows have this label?
Windows certified through the NFRC program carry it. If a quote has no ratings attached, ask for them before comparing prices.
Does low-E glass make rooms dark?
Modern spectrally selective coatings hold visible light while rejecting heat. Look at VT alongside SHGC rather than assuming a tradeoff.
Will new glass fix my condensation problem?
Sometimes, and it depends on the cause. See ways to reduce condensation.
See the Numbers on Your Quote
We’ll show you the rated values for the exact package we’re proposing, explain what they mean on your elevations, and price alternatives if you want to compare.
Big Easy Windows serves New Orleans, Metairie, and the surrounding metro. Call (504) 384-8165 or request an estimate.
