Certified Replacement Windows
Check for quality of replacement windows by their labels that certify standards created by the AMA and NWWDA, as well a possible energy star rating. Vinyl replacement windows that pass the AAMA/NWWDA standard are above average windows. Energy star certification shows energy savings, and usually exceeds most building codes, while the NFRC standards also measure energy efficiency. Check this list of manufacturers for the "seals of approval" they carry.