Window air-leakage ratings: ask about the product and the opening

Questions covered in this guide

Record where the draft seems to occur

Note the room, weather conditions and whether the window is fully closed and locked. Mark the location you notice: near the moving sash, surrounding trim or another nearby surface. These observations help direct an inspection; they do not identify the cause by themselves. Avoid assuming that every uncomfortable spot requires a completely new window.

Ask for the relevant measure

NFRC includes air leakage among window performance measures. It separately rates heat transfer using U-factor. Request the available air-leakage documentation for the proposed product and keep it separate from the U-factor. If a seller answers a draft question only with a thermal rating, ask how the actual leakage concern will be assessed. Record a missing value as missing rather than inventing one from the product name.

Compare the product and installation scopes

Create one column for the window specification and another for the surrounding-opening work. Ask which existing components stay, how the installer will inspect the opening, and what sealing work the proposal includes. Request an explanation of how discovered damage or a different leakage path would change the scope. For a repair proposal, identify the component being addressed and what condition remains. Compare those answers with replacement rather than assuming a favorable product rating resolves an undocumented installation problem.

Set a clear follow-up expectation

Ask the installer to document the completed work and explain whom to contact if the original concern persists. Keep the observed symptom and agreed scope with the final product details. Use a supplied price to compare repairs separately from replacement; the window calculator estimates supported replacement scenarios, not diagnosis or draft elimination. A rating is useful evidence for comparing products, while the actual opening still needs an appropriate assessment.

Sources and supported claims

NFRC includes air leakage among window performance measures.
Source ↗ · national · Checked 2026-10-12

It separately rates heat transfer using U-factor.
Source ↗ · national · Checked 2026-10-12