1. How long will the project take? A good crew can install ten 3-by-5-foot double-hung replacement windows in a day.
2. What level of service will you provide? The installer should remove the old windows and other debris (what will they charge for that, if anything?) and protect your home and landscaping.
3. Is your work certified or factory authorized? Installers may be certified by InstallationMasters, which is good. But factory-authorized installers are better because they have been trained to install a specific product.
Note: Contractors doing work in a home (or child-occupied building) built before 1978 that will disturb painted surfaces must be certified by the Environmental Protection Agency as a lead renovator. If your project is affected, check to see whether installation will cost more.
4. What if something goes wrong? Make sure you know whom to call. If the company that sold you the windows subcontracted the installation to another company, do you call the salesman or the installer?
5. What warranties will I receive? Most manufacturers guarantee their products for ten to 20 years (usually 20 years for glass and ten years for other components), assuming "proper installation." You may get a better warranty with factory-authorized installation.