Spacers between the glass for Replacement windows
When comparing energy efficiency in replacement windows, one of the most important features is the spacer between the glass. Most windows use a metal spacer which makes the interior window glass colder in the winter and warmer in the summer when compared to the use of a nonmetallic spacer. In the winter months, a nonmetallic spacer keeps more heat inside the house because it does not allow as much heat to be transferred to the outside as a metallic spacer does. This will save you money because your furnace will not have to run as much. In the summer months, a nometallic spacer allows less heat to enter the house from the outside when compared to a metallic spacer. This will save you money because your air conditioner will not have to run as much.
Another benefit of a nonmetallic spacer is that it absorbs more of the outside noise than a metallic spacer does. This makes it quieter in the house. The reason I know this is because we sold and installed windows for two customers who were friends and lived along the train tracks. One of the friends complained that her windows were noisier than her neighbor. We explained to her that she had purchased a less expensive window with a metal spacer while her friend had purchased a window which had a nonmetallic spacer.