Windows let the sunshine in, but in many cases, they also let the heat in (or out, in the winter). According to the U.S. Department of Energy, heat transfer through windows can account for 10 to 25 percent of your heating and air conditioning costs. Older, single-paned windows are the biggest energy wasters.

Many air leaks are easy to find because they are easy to feel – like those around windows, doors, and through electrical outlets. But hidden air leaks in attics, basements, and around chimneys are often more significant sources of energy loss. Consider addressing these big leaks first because they will have a greater impact on improving your comfort and reducing your utility bills. ENERGY STAR’s Home Sealing Do-It-Yourself Guide has great pictures and suggests places to look for these leaks. Visit ENERGY STAR Home Sealing for more information.

According to the National Association of Realtors, window replacements are among the home improvements offering the biggest return on investment. In fact, homeowners can generally expect to retrieve at least 70-80 percent of their investment in window replacements. That’s why Forbes calls window replacement a “recession-proof” home improvement. Learn the benefits of window replacement.

Consumer Tax Incentives: Insulation, Windows, Sealing

What is the tax credit for existing homes?
Existing homes are eligible for a series of efficiency measures. For some measures, such as insulation, a taxpayer can take a credit of up to 10% of the cost. There is a $500 cap on the credit per home, including the amount received for heating and cooling equipment, as described in the next section. Lower caps are set on credits for some individual measures.

These credits are available for buildings or systems placed in service from January 1, 2009, through December 31, 2009.

Read an IRS summary of the credit: Click here

What is eligible for the federal tax credits?

Eligible measures are:

• Added insulation to walls, ceilings, or other part of the building envelope.
• Replacement windows and skylights: credit capped at $200.
• Window Films
• External doors
• Sealing cracks in the building shell and ducts to reduce infiltration and heat loss.
• Pigmented metal roofs, or an asphalt roof with appropriate cooling granules.

Only materials (insulation, windows, sealants, etc.) are eligible and not the labor to install these materials.

Efficiency levels that qualify for the incentive are:

• Added insulation and replacement doors to bring insulation and doors up to levels specified in the 2001 IECC model energy code.
• Replacement windows meeting the requirements in the 2000 IECC model energy code. Energy Star windows will always qualify. In addition, storm windows are eligible if the existing window plus the new storm window meet the window requirements in the 2001 IECC.
• Certain window films are eligible for the tax credit if the manufacturer certifies that the specific window film satisfies the requirements of a “qualifying insulation system,” and the manufacturer certifies the product as meeting those requirements, the product is eligible for the tax credit of 10% of the cost of the materials (not installation labor), up to the $500 cap.
• Sealing cracks and holes in the building shell and ducts – under the IECC these should be sealed so sealing remaining leaks is consistent with the IECC.
• Roofs: metal roofs with pigmented coatings or asphalt roofs with cooling granules must meet Energy Star requirements.

New- View IECC Climate Zones by state and county, and IECC 2004 Supplement Edition R-values and U-factors for insulation, windows, and doors (8MB PDF).

Manufacturers and retailers should be able to help you tell whether a specific product qualifies.

What do I need to do to qualify for the incentives?
Under the IRS rules, manufacturers need to certify that specific measures are eligible. Homeowners should obtain a copy of this certification from the manufacturer, installer or retailer when buying these products. Certifications need not be submitted to the IRS, but should be kept on file in case the IRS has questions. Homeowners should also make notes on when each eligible measure is installed- only measures “placed in service” in 2009 are eligible.

So what else do I need to know?
Before you invest in any of these projects, be sure to read all the fine print. Some of these tax credits have restrictions. For example, eligible replacement windows have the Energy Star designation.

And don’t forget that you may be eligible for additional state or local incentives. You can find out more about what’s available by visiting the Database of State Incentives for Renewable and Efficiency.

Whether replacing windows in an older house or choosing windows for a new house, your decisions on what type of windows to buy will be among the most important decisions you will make in terms of energy use. Because of the impact windows have on both heat loss and heat gain, proper selection of products can be confusing. To get the most up-to-date information on what to look for in energy-efficient windows for your home, visit the Efficient Windows Collaborative.

Basic Features to Look for in a New Window:

• Reliability and good installation. Choose windows with good warranties against the loss of the air seal, and be sure to have experienced contractors install your high-tech windows. Consumers should recognize that the manufacturer’s quality control at the factory and care during shipping can have a big impact on the window’s air tightness at a site.
• Certified by ENERGY STAR. Windows, doors, and skylights qualifying for the ENERGY STAR label must meet requirements tailored for the country’s four broad climate regions: northern, north-central, southcentral, and southern. ENERGY STAR windows must carry the NFRC label (discussed below).
• Proper dimensions. To maximize energy performance, choose windows with larger unbroken glazing areas instead of multi-pane or true-divided-light windows. Applied grills that simulate true-divided-light windows are fine; they do not reduce energy efficiency.
• Efficient frame material and sash construction. Wood is still the most common material in use, and it insulates reasonably well. Unless a thermal break is incorporated into the design, aluminum frames conduct heat very rapidly and are therefore inefficient. Vinyl (PVC) windows, or vinyl frames insulated with fiberglass, are the most efficient and tend to insulate better than wood.
• Air-tightness. Examine air leakage specifications carefully when selecting windows, but in general, casement and awning windows are tighter than double-hung and other sliding windows.
• Glazing with low emissivity. Low-e coatings made of a thin, transparent layer of silver or tin oxide are used on high-performance windows to reduce the solar heat gain without reducing visibility as much as older tinted glass. The variety and placement of the low-e coating on the window varies for different climate zones and applications. ENERGY STAR offers purchasing tips to help you find which windows are appropriate for you.
• Multiple layers of glazing. Double glazing insulates almost twice as well as single glazing. Adding a third or fourth layer of glazing results in further improvement. Some of these windows use glass only; others use thin plastic films as the inner glazing layer(s).
• The right thickness of air space. With double-glazed windows the air space between the panes of glass has a big effect on energy performance.The wider the space, the less heat can be conducted through that space (as long as it stays under about 1″).
• Low-conductivity gas fill. By substituting a denser, lower conductivity gas such as argon for the air in a sealed insulated glass window, heat loss can be reduced significantly.
• Proper edge spacers. The edge spacer is what holds the panes of glass apart and provides the airtight seal in an insulated glass window. Avoid traditional hollow aluminum spacers because they have extremely high conductivity. Instead, choose edge spacers that are thin-walled steel, silicone foam or butyl rubber. With new edge spacers, however, pay particular attention to warranties against seal failure.

Selecting New Windows for Your Home
Windows, doors, and skylights qualifying for the ENERGY STAR label must meet requirements tailored for the country’s four broad climate regions: northern, north-central, southcentral, and southern. ENERGY STAR windows must carry the National Fenestration Rating Council (NFRC) label, allowing comparisons of ENERGY STAR-qualified products on specific performance characteristics.

U-value. U-factor measures how well a product prevents heat from escaping. It is the inverse of R-value, which is familiar to many people as a measure of insulation thermal performance. The lower the U-value rating, the better the overall insulating value of the window. Typical U-values range from 0.20 to 1.20. The U-factor ratings listed on NFRC labels (and in the NFRC Certified Products Directory) take into account heat loss through the glass, window edge, and window frame.

Solar heat gain coefficient (SHGC). The SHGC describes how much solar energy is transmitted through a window. Solar heat gain can be beneficial—providing free passive solar heat during the winter months — or it can be a problem, resulting in overheating during the summer. Windows with high coefficients are designed for colder climates, while windows with low coefficients are designed for hotter climates.

Visible light transmittance. While SHGC describes the relative amount of solar energy that can pass through a window, the visible light transmittance is simply the relative amount of sunlight that can pass through, measured on a scale between 0 and 1. The higher the number, the greater the amount of light that can pass through.

Air leakage. Air leakage is already listed by many window manufacturers, in terms of cubic feet of air per minute per foot of crack. An optional air leakage value is included on NFRC labels and in the NFRC Certified Products Directory.

Condensation resistance. Finally, the ability of a window to resist the formation of condensation on the interior surface is very important in evaluating the relative durability of a window. The NFRC measures condensation resistance on a 0–100 scale. The higher the rating, the better that product is at resisting condensation formation. This rating is optional for new products, and it can not predict actual condensation.

Before buying a new heating or cooling system, it makes sense to tighten up your house first. The following steps will reduce your heating and cooling load, improve your comfort, and maybe even allow you to purchase a smaller—and less expensive—furnace or air conditioner when the time comes to replace your existing system.

Step 1: Consider an Energy Audit
Step 2: Find and Seal Air Leaks
Step 3: Insulate
Step 4: Upgrade Inefficient Windows & Doors
Step 5: Replace Old Windows

Windows can be one of your home’s most attractive features. Windows provide views, daylighting, ventilation, and solar heating in the winter. Unfortunately, they can also account for 10% to 25% of your heating bill. During the summer, your air conditioner must work harder to cool hot air from sunny windows. Install ENERGY STAR windows and use curtains and shade to give your air conditioner and energy bill a break. If you live in the Sun Belt, look into low-e windows, which can cut the cooling load by 10% to 15%.

If your home has single-pane windows, as many U.S. homes do, consider replacing them with new double-pane windows with high-performance glass (e.g., low-e or spectrally selective). In colder climates, select windows that are gas filled with low emissivity (low-e) coatings on the glass to reduce heat loss. In warmer climates, select windows with spectrally selective coatings to reduce heat gain. If you are building a new home, you can offset some of the cost of installing more efficient windows because they allow you to buy smaller, less expensive heating and cooling equipment.

If you decide not to replace your windows, the simpler, less costly measures listed here can improve their performance.

Cold-Climate Window Tips

• You can use a heavy-duty, clear plastic sheet on a frame or tape clear plastic film to the inside of your window frames during the cold winter months. Remember, the plastic must be sealed tightly to the frame to help reduce infiltration.
• Install tight-fitting, insulating window shades on windows that feel drafty after weatherizing.
• Close your curtains and shades at night; open them during the day.
• Keep windows on the south side of your house clean to let in the winter sun.
• Install exterior or interior storm windows; storm windows can reduce heat loss through the windows by 25% to 50%. Storm windows should have weatherstripping at all movable joints; be made of strong, durable materials; and have interlocking or overlapping joints. Low-e storm windows save even more energy.
• Repair and weatherize your current storm windows, if necessary.

Warm-Climate Window Tips

• Install white window shades, drapes, or blinds to reflect heat away from the house.
• Close curtains on south- and west-facing windows during the day.
• Install awnings on south- and west-facing windows.
• Apply sun-control or other reflective films on south-facing windows to reduce solar gain.

Long-Term Savings Tip

• Installing, high-performance windows will improve your home’s energy performance. While it may take many years for new windows to pay off in energy savings, the benefits of added comfort and improved aesthetics and functionality may make the investment worth it to you. Many window technologies are available that are worth considering.

Efficient windows may have two or more panes of glass, warm-edge spacers between the window panes, improved framing materials, and low-e coating(s), which are microscopically thin coatings that help keep heat inside during the winter and outside during the summer.

Shopping Tips for Windows

• Look for the ENERGY STAR label.
• Check with local utilities to see what rebates or other financial incentives are available for window replacement.
• High-performance windows have at least two panes of glass and a low-e (low emissivity) coating.
• Remember, the lower the U-factor, the better the insulation. In colder climates, focus on finding a low U-factor.
• Low solar heat gain coefficients (SHGCs) reduce heat gain. In warm climates, look for a low SHGC.
• In temperate climates with both heating and cooling seasons, select windows with both low U-factors and low SHGCs to maximize energy savings.
• Look for whole-unit U-factors and SHGCs, rather than center-of-glass, or COG, U-factors and SHGCs. Whole-unit numbers more accurately reflect the energy performance of the entire product.
• Have your windows installed by trained professionals. Be sure they’re installed according to manufacturer’s instructions; otherwise, your warranty may be void.

Source

Having a 1/16-inch unsealed crack around a window is like leaving that window open 3 inches. Decrease your heating bill and your energy use by sealing up air leaks.

Wood – Attractive and thermally efficient, but needs regular maintenance and is prone to decay.

Clad (either vinyl or aluminum) – Most of the advantages of wood, but with lower maintenance. Color choices are more limited.

Extruded vinyl – Low cost, low maintenance, and nearly as energy efficient as wood. Large windows may bow or warp in hot weather.

Extruded Aluminum – Durable and low maintenance, but will transfer heat and cold without an effective thermal break.

Fiberglass – Stronger than vinyl, thermally efficient. Must be painted on both the interior and exterior.

Heat transfer is expressed as U-value. The lower the U-value, the more energy efficient the window.

Solar gain is an asset in cold climates but a liability in hot ones. Solar gain in measured on a scale of 0 to 1, which is called the solar heat gain coefficient (SHGC). A higher number indicates more solar gain. Suggested ratings are as follows: Northern U.S. – .55 or above; Southern U.S. – .40 or below; temperate climates – .40 to .55.

Air leakage is measured in cubic feet per minute (cfm)per square foot of glass. The higher the number, the leakier the window. A rate of less than .30 indicates a good seal.

Visible transmittance (VT) is the amount of light that comes through a window. This is one factor you can judge yourself simply by comparing the views through different windows.