A room is uncomfortable and its windows are old. Before committing to replacement, you want to know whether the problem is the window itself, air leakage, shading, or insulation elsewhere.
Imagine an $8,000 replacement quote with hypothetical energy savings of $200 a year. Simple energy-only payback would be 40 years; at $400 a year it would be 20 years. These are invented inputs, not typical costs or promised savings. Comfort, damage, financing and service life need their own assessment.
What would you do first? Choose a next step below, then use the full guide to compare the work and assumptions in actual proposals.