Visible transmittance & condensation resistance reference
The other two NFRC-label numbers: Visible Transmittance (VT) for daylight and Condensation Resistance (CR) for winter fogging, by glazing.
Double pane, low-E typically has VT 0.50–0.60 (fraction of visible light through, higher = brighter) and CR 45–60 (condensation resistance, higher = less winter fogging). VT and CR are the other two NFRC-label numbers — they don’t set code but they matter for daylight and fogging; typical planning ranges, confirm on the label.
Calculator inputs
Beyond U-factor and SHGC, the NFRC label carries two more numbers that shape how a window feels to live with. Visible Transmittance (VT) is the fraction of visible light that comes through, from 0 to 1 — higher means a brighter room. Condensation Resistance (CR) is a 0–100 rating of how well the window resists interior fogging in cold weather — higher means less winter condensation on the glass.
Neither sets code, but both affect comfort and durability. Adding panes and low-E coatings lowers U-factor and SHGC (good for energy) while gently reducing VT (dimmer) and raising CR (drier glass in winter). This reference gives typical planning ranges by glazing so you can spot an outlier on a spec sheet.
Formula
VT and CR are measured ratings read off the NFRC label, not derived from a formula. General trend:
more panes / more low-E → lower VT (dimmer) · higher CR (drier glass)
Worked example
A typical double-pane low-E unit lands around VT 0.50–0.60 and CR 45–60. Step up to triple-pane low-E and VT eases to about 0.40–0.55 while CR climbs to roughly 55–70 — a little less light, noticeably less winter fogging.
When to weight daylight vs dryness
When each number matters. Prioritize a high VT for north-facing rooms or anywhere you want maximum daylight; a very low SHGC coating can also cut VT, so check both if a room feels dim. Prioritize a high CR in cold climates or high-humidity rooms (kitchens, baths) where interior condensation can damage sills and sashes over time. These are labeled planning ranges — the exact VT and CR are on the product’s NFRC label; pair with the SHGC reference for the full label picture.
Reference table
| Glazing | Visible transmittance (VT) | Condensation resistance (CR) |
|---|---|---|
| Single pane | 0.80–0.90 | 25–35 |
| Double pane, clear | 0.70–0.80 | 35–45 |
| Double pane, low-E | 0.50–0.60 | 45–60 |
| Triple pane, low-E | 0.40–0.55 | 55–70 |
Labeled typical planning ranges — the exact VT and CR are NFRC-rated on the product label.
Frequently asked questions
What is visible transmittance (VT) on a window?
VT is the fraction of visible light that passes through the window, from 0 to 1. A higher VT means a brighter room; typical double-pane low-E units run about 0.50–0.60.
What is condensation resistance (CR)?
CR is a 0–100 NFRC rating of how well a window resists interior condensation in cold weather. Higher is better; more panes and low-E coatings raise CR, so triple-pane units fog less than single-pane.
Do low-E windows make a room darker?
Slightly. Low-E coatings and extra panes lower VT a little, and a very low-SHGC coating can dim a room more. If daylight matters, compare VT figures and favor a spectrally selective low-E that cuts heat while keeping light.
How do I stop condensation on new windows?
Choose glazing with a higher condensation resistance and control indoor humidity (ventilation, exhaust fans). CR predicts the glass’s resistance, but very humid indoor air can still fog even a good window.