Energy Efficient Windows in Richmond, VA

Two panes, a sealed gap filled with argon, and one low-E coating: this is the standard efficient window, and the baseline every other option here gets measured against. The NFRC's consumer guide calls argon the popular, affordable gas fill. Some gas escapes over the years, at about 0.5% a year for an efficient unit, so after 20 years the window still performs at roughly 90% of where it started. HomeGuide puts double-pane windows at $400 to $2,000 each installed, nationally. The spread comes from size, style and frame material.

A triple-pane unit adds a third layer and a second low-E coating, with about half an inch of argon or a quarter inch of krypton in each gap, per the NFRC guide. Krypton insulates better in a thin space but costs more. HomeGuide prices triple-pane windows at $450 to $3,000 installed and notes the glass weighs 25% to 50% more than double-pane, which means heavier sashes and can mean an extra installer on big units. The NFRC guide recommends low-solar-gain triple glazing for climates with significant heating and cooling loads. Richmond counts about 3,736 heating degree days and 1,561 cooling degree days in a normal year: mostly a heating climate, with summers that still matter.

Low-E coatings are transparent metallic layers thinner than a human hair, and the NFRC guide says they can cut a window's energy loss by as much as 40%. They aren't all the same. High-solar-gain low-E, often a pyrolytic coating, lets winter sun through to warm a room. Low-solar-gain low-E, usually a sputtered coating with two or three silver layers, blocks more of the sun's heat. Our view: in Richmond, a low-solar-gain coat belongs on west and south glass that overheats rooms in July, and the code's SHGC cap, described below, sets the ceiling for every pane in the house.

The spacer holds the panes apart and keeps the gas in. Metal spacers pass heat and cold easily and invite condensation along the glass edge; non-metal spacers block that best, and warm-edge systems blend metal and non-metal parts to cut it, the NFRC guide explains. Since July 2010, the glass units in ENERGY STAR windows have had to be certified through recognized programs that test them against heat, humidity and UV. Air slipping past a worn weatherstrip undoes part of what good glass buys, which is why ENERGY STAR also caps air leakage, at 0.3 cfm per square foot.

Laminated glass bonds a plastic interlayer between two lites, the same idea as a windshield. For sound, a glass supplier's guide rates a single quarter-inch pane at STC 31, some laminated glass at 40 or more, and a double-pane unit with laminated glass at 45 to 50. A typical house wall rates about STC 33. HomeGuide prices double-pane windows with laminated glass at $600 to $1,600. Gaps cancel the gain, though: the same guide notes an STC-50 assembly can drop into the mid-30s through small cracks, so the seal around the frame matters as much as the glass.