| Scope | Estimated range |
|---|---|
| Exterior aluminum | $60 – $160 |
| Exterior with Low-E | $110 – $240 |
| Interior acrylic panel | $70 – $190 |
| Custom / oversize | $180 – $425 |
| 8 windows total | $480 – $3,400 |
Ranges reflect installed cost including materials and labor for typical residential work. The low end of each range corresponds to a basic vinyl configuration; the high end reflects premium frames, upgraded glazing, and larger units. Last reviewed 2026-11-12.
The original window stays in place and a second sash or panel mounts outside it. That preserves the original window, which matters in historic districts where replacement is restricted, and it is why storm windows remain the default in older neighborhoods.
The trapped air space provides the insulation. Too tight and the gap traps moisture against the original window; too loose and it loses effectiveness. Correct units have weep and vent provisions, and incorrect installation causes the very rot people blame on the window.
Exterior storms take weather and debris but are easier to clean from outside. Interior storm panels are cheaper, easier to install, and popular in cold climates, but they must be removed seasonally in many homes to allow ventilation.
They reduce air infiltration and add an air gap, so yes, but the savings are smaller than replacing the window. On original single-pane windows the improvement is meaningful; on modern double-pane windows it is marginal.
Improperly vented exterior storms can trap moisture against the original sash and accelerate rot. Correctly installed units have weep holes and vents, and that detail is what separates a protective storm from a damaging one.
If the original windows are sound and you want to keep them, storms are far cheaper. If the original windows are failing, leaky, or painted shut, storm windows preserve a failing window and the money is better spent on replacement.