"So much about selecting a good window comes down to the warranty," says Chris Mathis of MC2 [squared], a building-science consulting company based in Asheville, N.C. Mathis, a founding board member and the former director of the National Fenestration Rating Council, insists that a window's warranty should be one of the first selection criteria to consider, regardless of window materials and features. "If a window fails in a few years, it doesn't matter how good or strong or energy efficient it started out to be," Mathis says. "About 30% of the replacement windows installed are replacing windows that are only about seven years old. This speaks to how poor many of the units our there are."

The most common window failure is the seal on an insulated glass unit. Once the seal blows, the window fogs up between the panes. This can cause a drastic reduction in window R-value and may oxidize the low-E coating, turning it into a high-E coating that absorbs heat rather than reflecting it. In the worst cases, the pane actually deforms, bowing inward as a gas fill, such as argon, escapes.

Mathis recommends choosing a window with a minimum 20-year warranty on the insulated glass. "There are so many window makers out there," he says, underscoring that it doesn't take much to get into the window manufacturing business and capture local markets with cut-rate pricing. But those are the companies, Mathis cautions, that may not be around in three or five or seven years when the glass fails.

Warranty wording. Mathis recommends staying up late if that's what it takes to read the fine print on any window warranty. Many warranties cover a lot up front, but that coverage quickly declines when all the details are spelled out. The following are some warranty types and language to look for:

  • Non-prorated warranties will cover the entire purchase price of the window for the term of the warranty. Remodelers are familiar with prorated warranties on roofs, but a well-made window shouldn't degrade with exposure as rapidly as roofing materials do, so there is little justification for such a warranty structure.
  • Fully transferrable warranties are a sign that the window maker means business. For a homeowner selling ahome, it can be a value-added feature that the remodeler ought to make available when recommending a window.
  • Non-glass component warranty. Hardware, in particular, should carry a minimum 10-year warranty. A good window with bad hardware is a bad window, Mathis insists. If a lock breaks or a crank handle strips out, it will reflect poorly on the remodeler who instaled the window. Think about the window manufacturer's capacity to stock replacement parts well into the future.
  • Labor and installation. Unless a certified representative of the manufacturer installed the unit, few warranties will cover the cost of installation. Some may, but largely this will fall to the remodeler who installed the window—even more reason for remodelers to stick with brands they can trust.
  • Exclusions. Some warranties specifically exclude coverage for damage from environmental factors such as high humidity or salt spray, making installation especially inappropriate in many locations. Often the exclusion applies to the glass as well as the hardware and finishes.
  • Finishes. Coverage on finishes is rare, but some warranties do cover exterior coatings and finishes on cladding. However, painting or refinishing the exterior to match the home may null this coverage. This is particularly true with warranties on aluminum-clad and vinyl units.