How to Read a Window Energy Label (and What Matters in Upstate NY)
The NFRC label on a window lists four numbers. U-factor measures heat loss and lower is better, which is the main one in our climate. Solar heat gain coefficient measures solar heat entering. Visible transmittance measures light. Air leakage measures infiltration, where lower is better.
Every new window carries a white NFRC label with four numbers on it. Those numbers are independently certified and they are the only honest way to compare two windows, because they are measured the same way regardless of what the brochure claims.
Most salespeople will happily talk about anything except these numbers. Here is what each one means and what to want in a heating-dominated climate like ours.
The four numbers
| Number | Range | What it measures | What to want in Albany |
|---|---|---|---|
| U-Factor | 0.15 to 1.20 | Heat loss through the whole assembly | As low as budget allows, this is the main one |
| Solar Heat Gain Coefficient | 0 to 1 | Fraction of solar heat passing through | Moderate, higher acceptable on south walls |
| Visible Transmittance | 0 to 1 | Fraction of visible light passing through | Higher keeps rooms bright |
| Air Leakage | 0.1 to 0.3 | Air passing through the assembly | Lower is better, 0.3 or below |
U-factor is the inverse of R-value. A U-factor of 0.25 is roughly equivalent to R-4. Windows will never approach wall insulation values, which is why window count and size matter for whole-house energy use.
Why the climate zone on the label matters
ENERGY STAR certifies windows by climate zone, and the criteria are different in each. The Capital Region sits in the Northern zone, where heating dominates for roughly seven months of the year. A window certified for the Southern zone is optimized to keep solar heat out, which is the opposite of what a house in Albany wants on a January afternoon. When someone shows you an ENERGY STAR sticker, the question is which zone. A generic ENERGY STAR claim without a zone tells you almost nothing.
The solar heat gain nuance most people get backwards
In a cooling-dominated climate you want a low solar heat gain coefficient, because solar heat entering is a cost. Here, for about seven months, solar heat entering is free heating. On a south-facing wall with good winter sun exposure, a moderate rather than very low solar heat gain coefficient can measurably reduce your January heating load. The trade-off is summer, but our cooling season is short. On north-facing walls it is irrelevant because there is no direct sun. On west-facing walls with afternoon summer sun, a lower number helps with overheating. This is why specifying a single glass package for the whole house is a simplification rather than an optimization, though for most homes it is a reasonable one.
Air leakage: the number nobody quotes
Air leakage measures how much air passes through the window assembly at a standard test pressure, and it is the number most likely to be missing from a sales conversation. It matters enormously on exposed sites, because infiltration scales with the pressure difference across the wall and a house on an open hilltop in Brunswick or below the escarpment in Altamont sees pressures a sheltered subdivision never does. Window style drives this more than brand: casements and awnings seal by compression and score better, while double hungs and sliders seal by sliding past weatherstripping and score worse. If drafts are your actual complaint, this is your number.
How to use the label when comparing quotes
- Ask every contractor for the U-factor and air leakage rating of the specific unit they are quoting, in writing.
- Compare those numbers directly. They are independently certified and mean the same thing across manufacturers.
- Confirm the ENERGY STAR certification is for the Northern climate zone, not just ENERGY STAR generally.
- Check whether the U-factor quoted is for the whole window or center of glass only. Whole window is the honest figure and it is always higher.
- If two quotes have similar numbers and very different prices, the difference is in construction quality and warranty, not performance.
- A salesperson who cannot produce these numbers is not someone to buy from.
Ranges reflect typical Capital Region projects and are for planning only. Every Sundog quote is written, itemized, and free.
Frequently asked questions
What is a good U-factor for windows in upstate New York?
Lower is better and the ENERGY STAR Northern zone threshold is the benchmark to ask about, since it is set specifically for heating-dominated climates. Ask the contractor for the whole-window U-factor of the specific unit quoted. Center-of-glass figures look better and are not what the assembly actually delivers.
Is a lower SHGC always better?
No, and this is the most commonly misunderstood number. In a cooling-dominated climate, low is better. In a heating-dominated climate like ours, a moderate solar heat gain coefficient on south-facing windows gives you free winter heat during the day. Very low SHGC glass is optimized for a problem we do not really have.
What does whole window versus center of glass mean?
Center of glass measures performance at the middle of the pane, away from the frame and the spacer. Whole window includes the frame and the edge of glass, which perform worse. Whole window is the honest number and the one NFRC certifies. If a quote shows a suspiciously good U-factor, check which one it is.
Does the NFRC label appear on every window?
On every new window sold in the United States that participates in the program, which is essentially all mainstream products. The label is a temporary sticker on the glass at delivery. Take a photo of it before it is removed, because it is the record of what you actually received.
How much difference does air leakage actually make?
On a sheltered suburban lot, modest. On an exposed hilltop or a windward elevation, substantial, because infiltration scales with wind pressure. If your complaint is drafts rather than cold glass, air leakage is likely your problem and window style matters: casements seal by compression and outperform double hungs and sliders on this number.
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