Unfortunately, our home’s windows can also let out heat during the winter and cool air during summer. Inefficient glazing materials, blown window seals and rotted framing can combine to strip your home of its energy efficiency and leave you in discomfort — resulting as much from soaring utility bills as from temperature variations.
If you’re looking for a strategy to beat rising fuel costs, increase your comfort and save natural resources in the process, the clear choice may be to start with your home’s windows. For centuries, homeowners had one window option: single-pane. Today’s array of choices, however, includes innovative glazing and framing materials that not only help to lower utility bills but also make use of recycled content and cutting-edge technology to minimize their manufacturing impact on the environment.
“With the expected high cost of natural gas this fall and winter, choosing energy-saving products is a must for any consumer,” says Kathy Krafka Harkema, corporate public relations specialist for Pella Windows. “To avoid the sticker shock of high utility bills, consumers should look around their home and identify where replacing or updating windows would result in a better long-term return on investment and short-term defense against high energy prices.”
Frame materials
By far the most common material in window frame construction, wood is a renewable resource. From a thermal point of view, wood-framed windows perform well and have great insulating properties. Unfortunately, wood is susceptible to rot and needs occasional painting to protect it from environmental damage and to maintain its appearance. To combat this weakness, manufacturers often treat wood window frames with a preservative, and many offer aluminum cladding to minimize maintenance.
Vinyl, also known as polyvinyl chloride (PVC), is a versatile plastic with good insulating value. In terms of thermal performance, insulated vinyl frames are comparable to wood. Because vinyl is maintenance-free, you’ll never need to waste time or money on painting, and excess vinyl from the manufacturing process can be recycled and reused.
Some people are concerned about potential health risks because all types of vinyl release airborne volatile organic compounds (VOCs) that can cause a variety of ailments. However, the hard vinyl used in window manufacturing does not off-gas VOCs nearly as much as soft vinyl (the material used as flooring), and any health risk posed by vinyl windows is negligible.
Fiberglass is a relative newcomer to the window market. Technically referred to as glass-fiber-reinforced polyester, fiberglass has the lowest overall environmental impact, and when the frame’s air cavities are filled with insulation, its thermal performance is superior to both wood and vinyl. Because fiberglass is stronger than vinyl, it can be used to produce thinner window frames (which allows room for more glass and a larger viewing area). In addition, fiberglass can be powder-coated instead of being stained or painted, eliminating harmful VOCs from the finishing process (and any over-sprayed powder can be swept up and reused).
Aluminum windows have been on the market for decades. They’re strong, light, durable and maintenance-free. However, aluminum has a high thermal conductance, and as a result, it readily transfers heat. In cold climates, aluminum frames can become cold enough for ice to form on their interior surfaces. And although manufacturers have developed thermal breaks within the frames to aid insulation, in general aluminum is not considered a viable material for high-efficiency window frames.
Glass technology
In addition to producing better window frames, manufacturers have made significant improvements to window glass during the last few decades. The result of these improvements is better thermal performance, which decreases fuel demand for heating and cooling needs (meaning more money in your pocket).
To improve the energy performance of window glass (also referred to as glazing), manufacturers use three fundamental technologies, often in combination. The first involves altering the glazing material’s chemical composition or physical characteristics, such as with tinted glazing. The second involves applying a special reflective material, film or coating (such as a low-e coating; see “Window Terminology,” p. 44) to the glazing surface to reduce both glare and heat gain and to improve heating and cooling performance. The third involves assembling multiple layers of glass within a single window and controlling the properties of the spaces between the layers through the use of insulating spacers and inert, low-conductance gases such as argon or krypton.
A sensible approach
Although replacing old windows with new energy-efficient units can be expensive, it does not need to be cost-prohibitive. Rather than tackle your whole house at once, consider replacing windows room by room. And doing the work yourself rather than hiring a contractor can save a substantial amount of money. In some cases, homeowners can receive tax credits for installing energy-efficient windows. In the end, you may discover that your annual energy savings and the increased comfort within your home are well worth the expense.
Window Terminology
Air leakage (AL): An indication of how much air will pass through cracks in a window assembly — the lower the AL, the less air will pass through.
Argon gas: An odorless, colorless, tasteless, nontoxic inert gas, six times denser than air, that’s used to replace air between the glass panes to reduce temperature transfer.
Condensation resistance (CR): A measure of a window’s ability to resist the formation of condensation on its interior surface — the higher the CR rating, the better the ability to resist the forming of condensation.
IGU: An abbreviation for insulated glass unit, it consists of two or more panes of glass separated along the edges by a spacer system and elsewhere by airspace that acts as an insulator.
Krypton gas: Similar to argon gas, krypton gas is 12 times denser than air and is used in place of argon gas when even greater energy efficiency is required.
Low-e: Most often used in reference to a thin metallic-oxide coating applied within the panes of high-performance windows that increases the U-value of the window by reducing heat flow from a warmer airspace to a colder glazing surface.
R-value: A unit of thermal resistance used for comparing insulating values of different materials — the higher the R-value of a window, the greater its insulating properties and the slower the heat flows through it.
Solar heat-gain coefficient (SHGC): Measured between 0 and 1, the SHGC measures how well a window blocks heat caused by both direct sunlight and absorbed heat — the lower the number, the greater the window’s ability to reduce solar heat gain.
U-factor: The thermal performance of windows is commonly stated in U-values. A measure of a material’s ability to conduct heat, U-value is equal to 1/R (R-value) — the lower the U-value, the better the material’s insulating capacity.
UV block: The percent of ultraviolet rays blocked from being transmitted through the glass — the higher the number, the lower the percentage of ultraviolet rays transmitted through the window.
Visible transmittance (VT): A measure of the amount of light that passes through a window — expressed between 0 and 1, the higher the VT, the more light a window transmits.
INSTALLATION
Installing energy-efficient windows does not need to be an expensive job reserved for professionals. Many window manufacturers support homeowner installations, and with a little care and patience, you can achieve the same results as a contractor. We worked with Simonton Windows to develop these basic steps for a typical window replacement. Bear in mind that our process may vary slightly from a specific manufacturer’s recommendations — you should always follow the instructions for the unit you are installing. And remember: Before you purchase a new window, remove both the existing window’s interior and exterior trim and measure the rough opening; you’ll need those dimensions to order the right size.
To begin, apply masking tape across the old window — if the glass breaks, the tape will help to hold the shards in place. Remove the nails that secure the window to the framing. Depending on how the window is attached, you may need to use a reciprocating saw to cut the nails that secure it (photo 1); then gently remove the old unit from the opening .
Apply flashing tape to the sill. Make sure that the tape extends 6 in. up each side of the rough opening and overlaps the front of the opening by 1 in. If necessary, apply a second row of flashing tape so that it overlaps the first by 1 in. Make sure that the tape does not extend past the interior face of the rough opening (photo 2).
Check that the sill is level and fasten any shims that are required; then gently fit the new window into the opening. Position the bottom of the window into the opening first; then tip the unit into place. Center the window between the sides of the opening to allow clearance for shimming, and drive one 2-in. galvanized roofing nail into the corner on each end of the top nailing fin to hold the window in place. Position shims 1 in. from the corners of the window and adjust them as needed until the window is plumb and square within the opening; then place shims at the midpoint of the window sides for added support. Finally, drive roofing nails through the nailing fins to firmly secure the window to the framing (photo 3). Check for proper operation; then apply flashing tape over the nailing fins.
Slide drip edge under the siding at the top of the window; then reattach the exterior trim pieces (photo 4) — make sure that the drip edge overlaps the top trim piece once it’s in place — and apply a bead of caulk around the window’s perimeter. From inside, fill any voids with low-expansion foam — be careful to not apply too much foam, as you could bow the window. Once the foam has set, reattach the interior trim pieces.