Compare the exact product, rating, installation method, water-management scope, finish work, warranty, and closeout record at every opening.
Two window quotes are comparable only when they describe the same opening, product, glass package, installation method, finish work, and warranty. A low total can hide insert installation where the other contractor priced full-frame work, or exclude the trim and water-management details that make the opening complete.
List the problem at every opening
Number the windows and record room, approximate size, operating style, frame material, visible damage, condensation location, water staining, drafts, difficult operation, lock condition, and the comfort problem you want solved. Take one exterior and one interior photograph. Do not treat between-pane fog, room-side condensation, and wall leakage as the same defect.
Some complaints come from air leakage around the opening, failed flashing, shade, humidity, or nearby heat loss rather than the glass alone. Ask each bidder what was observed and whether repair, weatherstripping, storm windows, or selective replacement was considered. Replacing every unit before naming the failure is not a diagnosis.
Put the exact product on the quote
Require manufacturer, product line, operating type, frame material and color, glass construction, grids, hardware, screens, safety glazing, and each opening’s unit count. Ask for the National Fenestration Rating Council label values, including U-factor and solar heat gain coefficient, for the exact configuration. NFRC explains that a lower U-factor means less heat loss; SHGC describes solar heat admitted through the product.
The best rating depends on climate, orientation, shade, and the room. ENERGY STAR uses climate-specific criteria, so “triple pane” or “low-E” by itself does not settle performance. Keep the product identifier and label in the house file so a later warranty claim refers to the installed unit, not a brochure family.
Separate insert from full-frame installation
An insert usually preserves the existing frame and trim. Full-frame replacement removes more of the old assembly and can expose framing, flashing, insulation, rot, or prior installation defects. The quote should name which method applies to each opening and why, plus how hidden damage will be documented and priced before extra work proceeds.
Spell out removal, sill and framing preparation, flashing or water-management work, insulation, air sealing, shimming, fasteners, exterior sealant, interior and exterior trim, paint or stain, disposal, permits, cleanup, and protection of floors and furnishings. Ask who handles alarms, shades, security sensors, masonry, siding, or stucco that the project disturbs.
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Flag lead paint and water damage before demolition
Work that disturbs paint in a pre-1978 home may fall under EPA’s Renovation, Repair and Painting requirements. Ask how the contractor will determine applicability, contain dust, protect occupants, clean, and document the work. Suspected rot, mold, structural damage, or active leakage needs its own cause and repair scope; a new window should not simply cover it.
Compare warranty and payment language
Put product, glass, finish, hardware, seal-failure, labor, and installation warranties in separate rows. Note exclusions, transfer rules, service fees, registration, who files a claim, and whether labor to remove and reinstall finishes is included. Match deposits and progress payments to identifiable work rather than calendar dates.
Use the contractor quote comparison for licensing, insurance, permits, and change-order questions. Choose the proposal that makes the installed opening and closeout record clearest. The cheapest window package is expensive if the quote leaves the wall unfinished or the leak unexplained.