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Questions to ask before you hire a window installer

A careful window installer measures accurately, matches the right replacement method to your openings, manages water with proper flashing (not just caulk), and leaves you with clear NFRC ratings and written warranties. Use these questions to separate crews who treat windows as a building envelope job from door-knock sales pitches that push the same “energy package” on every house.

Questions to ask

1. Are you recommending full-frame (tear-out) replacement or insert (pocket) windows — and why for my openings?

Why it matters: Inserts slide into the existing frame and are faster and often cheaper, but they shrink the glass area and leave rotten or out-of-square frames in place. Full-frame replacement removes the old window to the rough opening so flashing and structure can be fixed. Ask which method they recommend for each opening and how they check for rot, settlement, or failed frames before locking the quote.

2. What frame material and glass package are you quoting (vinyl, fiberglass, wood, aluminum, clad) — with brand and series names?

Why it matters: “Vinyl windows” is not a product. Ask for manufacturer, series, and whether the glass is dual- or triple-pane, Low-E coating type, and gas fill. Different materials expand, maintain, and last differently in sun and cold. A quote that only says “premium energy windows” without model numbers is hard to compare or warranty later.

3. What are the NFRC ratings for the exact units — U-factor, SHGC, and VT — and do they meet local energy code?

Why it matters: U-factor measures heat transfer; SHGC measures solar heat gain; VT is visible light. Lower U-factor generally means better insulation; SHGC should match your climate and orientation (south glass is not the same problem as west glass). Ask for ratings on the labeled units you’ll receive, not a brochure average, and whether permits require ENERGY STAR or code-minimum values in your city.

4. Who measures the openings, and what happens if a custom unit arrives wrong?

Why it matters: Custom windows are made to measure; a half-inch error means delays and change orders. Ask whether the installing company measures (not only a salesperson), how they handle out-of-square openings, and who pays if the factory unit doesn’t fit because of their measurement. “We’ll foam and trim it” is a warning when the rough opening was never verified.

5. How do you flash and waterproof the install — sill pan, tape, and exterior seal — not just interior caulk?

Why it matters: Most window leaks start at the sill and corners when water isn’t directed out of the wall. Ask whether they use a sill pan or equivalent, how they integrate with housewrap or weather-resistive barrier, and what exterior finish work is included. Caulk alone is not a flashing system; if they can’t describe water management, you may be buying a future interior stain.

6. Is your crew trained for lead-safe work on pre-1978 homes, and will you contain dust during tear-out?

Why it matters: Disturbing old paint can create lead dust. In many U.S. jurisdictions, renovation work on pre-1978 housing triggers EPA RRP (Renovation, Repair, and Painting) rules: firm certification, trained renovators, and containment. Ask for certification proof and how they protect floors, HVAC returns, and living spaces. “We’ve done this for years” without lead-safe practices is a health and liability problem.

7. What’s included in the written price — windows, labor, disposal, interior trim, exterior finish, and permits?

Why it matters: Low ball window ads often exclude trim, paint, exterior cladding patches, or haul-away. Get a line-item or clearly scoped package: unit counts by size/type, install method per opening, interior casing/stool work, exterior cladding or brickmold, disposal, and permit fees. Agree that extras need your OK with an updated quote before the crew expands the job.

8. Who actually installs — your employees or subcontractors — and will the same company warrant the labor?

Why it matters: Some brands sell through dealers who subcontract install; warranty finger-pointing starts when glass is fine but the install leaks. Ask who is on your site, who supervises, and whether labor warranty is from the installer, the manufacturer, or both. Get labor and product warranties in writing with lengths and what voids them (homeowner finishing, storms, etc.).

9. What product and labor warranties am I getting, and how do I file a claim years later?

Why it matters: Glass seal failure, hardware, and frame warranties often differ from labor coverage. Ask for transferability if you sell the home, whether proration kicks in, and who to call for fogged glass vs a leaking flange. Lifetime marketing language that excludes seal failure or requires dealer involvement you can’t reach later is not a useful warranty.

10. What’s the lead time, install duration, and contingency if weather or backorders slip?

Why it matters: Custom units can take weeks; storm seasons and factory delays stack up. Ask for order-to-install timeline, how many days on site, whether openings stay boarded overnight, and what happens if a unit is damaged in shipping. A hard start date with no supply confirmation is how living rooms stay plywood for a month.

11. Do you pull required permits, and will you show manufacturer install instructions were followed?

Why it matters: Some cities require permits for window replacement, especially when structure, egress, or historic rules apply. Ask who pulls the permit, whether egress bedroom windows will still meet code after inserts shrink the opening, and whether you’ll get stickers/labels or a packet matching the installed units. Skipping manufacturer fastening and sealing details is a common path to denied warranty claims.

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