Window Restoration vs Replace Calculator

This calculator lines up two paths for a set of historic windows side by side: restore the originals and add storm windows, or rip them out and install new replacements. The restoration total is simply the per-window restoration cost (epoxy consolidation, reglazing, weatherstripping) plus a storm window added on top, multiplied across the window count; the replacement total is just the installed unit cost times the count. Subtracting one from the other gives the straight dollar savings restoration offers over full replacement — and in the vast majority of real-world cases restoration comes out cheaper, since even a good storm window rarely costs as much as a new sash-and-frame unit. On the energy side, the model takes the extra up-front cost of replacement over the restoration-plus-storm option and divides it by your estimated annual energy savings across all the windows to find a simple payback period: how many years of energy savings it would take for replacement's higher price tag to pay for itself.

Finally, it flags a real and often-overlooked risk: for a project claiming the 20% federal Historic Tax Credit (26 U.S.C. § 47), replacing original windows with new ones can disqualify the window portion of your Qualified Rehabilitation Expenditures from the credit entirely, since the National Park Service's Secretary of the Interior's Standards for Rehabilitation — detailed for windows specifically in NPS Preservation Brief 9, "The Repair of Historic Wooden Windows" — call for repairing and retaining original materials wherever possible and replacing them in kind only when necessary. The calculator estimates that potential credit exposure as 20% of the replacement total. Treat the energy-savings input carefully — it's a rough per-window estimate you supply, not a modeled figure, so pull it from an energy audit or storm-window manufacturer data rather than guessing, since the payback-years result is only as good as that number.