Is your furniture or carpet faded from the Sunlight's ultraviolet rays coming from the window? If so, you most likely would not have Very low-E glass that blocks the Sunlight's dangerous rays. U-value is definitely the measure of the speed of heat reduction And exactly how effectively a product insulates. https://replacementdoorsinkeswick86925.thelateblog.com/32650234/entry-doors-residential-in-keswick-ontario-things-to-know-before-you-buy