Tell Us About Your Windows
No technical ratings needed — just describe what you see and feel. We'll handle the building science.
What the Glass Is Actually Doing
🌡️ The Comfort Case for New Windows
The Building Science Behind Window Performance
A window's U-factor measures how fast heat travels through it — lower is better. Single-pane glass has a U-factor around 1.10, meaning heat moves through it quickly in either direction. A quality triple-pane window has a U-factor around 0.17–0.20, meaning heat moves through it at roughly one-sixth the rate.
But here's the part window salespeople rarely tell you: windows account for only about 10–25% of a home's total heat loss, depending on climate and how many windows you have. The ceiling, walls, floors, and especially air leakage all lose more heat — often significantly more. Which is why, in most homes, insulation and air sealing beat window replacement dollar for dollar on energy savings.
Where windows win is comfort. Cold glass surfaces in winter cause radiant discomfort — your body radiates heat toward that cold surface even when the air temperature in the room feels fine. Eliminating that effect is often worth more than the energy savings.
| Window Type | U-factor | Heat Loss Compared to Single Pane |
|---|---|---|
| Single pane (original) | 1.10 | Baseline — worst |
| Single pane + storm window | 0.75 | 32% less |
| Double pane, older (no coating) | 0.50 | 55% less |
| ENERGY STAR standard double pane | 0.30 | 73% less |
| High performance double pane | 0.25 | 77% less |
| Triple pane | 0.20 | 82% less |
U-factor is the inverse of R-value. A U-factor of 0.25 = R-4. That's why even the best windows (R-4 to R-7) are still far less insulating than a well-insulated attic (R-38 to R-60).
Common Questions About Window Upgrades
Are new windows a good investment?
It depends on your starting point. Single-pane windows in a cold climate — yes, the savings and comfort improvement are meaningful. Already have double-pane low-e windows that are sealing properly? Probably not — the marginal energy gain from upgrading further is small and the cost is high. In most cases, insulation and air sealing deliver better return per dollar.
I feel drafts near my windows. Do I need to replace them?
Not necessarily. Most window drafts come from air leaking around the window frame — not through the glass. Before spending thousands on replacement, try caulking the interior trim, checking the weatherstripping on operable sashes, and looking for gaps at the rough opening. If the draft disappears, you may have just saved a lot of money.
What does fogging between the panes mean?
It means the seal on your double-pane unit has failed and the insulating gas fill has escaped. The window is now performing much closer to a single pane. At this point, the glass unit (called an IGU) or the entire window should be replaced — it is no longer providing meaningful insulation value.
Should I replace all windows at once or do some first?
If budget is a concern, prioritize north-facing windows (most heat loss in winter with no solar benefit) and west-facing windows in hot climates (most afternoon solar heat gain in summer). South-facing windows in cold climates can actually provide net solar gain with the right glass coating — don't rush to replace them if they're structurally sound.