Every home needs a view to the outside and to allow natural light inside. The bad news is that glass by itself is a poor insulator so windows can be the leaking sieve of a house, allowing warm or cool air to escape at phenomenal rates.

Review:
We looked at two different aspects of windows, the frame and the glazing (the combination of glass, coating, films and gases). Each manufacturer puts frames and glazing together differently, but there are some common threads to all of the products.

Frames - Below is a chart showing the choices for window frames with advantages and disadvantages of each.

Frame Type   Advantages Disadvantages Cost Aluminum Very strong, lightweight, and durable with low maintenance. Consistent product due to manufacturing techniques. Low profile, allowing more light into your home. Less expensive than other frame types. Wide range of color and finishes. Very good conductor of heat, and bad thermal properties. Denting and wear can show and are hard to repair. Will expand and contract due to heating and cooling cycles. Low Thermally improved Aluminum All the advantages of aluminum, plus increased thermal performance owing to non-conductive thermal breaks. Not all of these products can report a substantial increase in thermal performance. And they will still dent and wear, expand and contract like regular aluminum windows. Medium Fiberglass Very strong. Dimensionally stable and will not expand and contract with temperature variations. Good thermal performance. Lower profiles. Air cavities can be filled with insulation for superior thermal performance. Durable and won't dent like metal frames. Fiberglass windows are hard to find. Unless insulated they still won’t outperform wood frames. High price point. High Vinyl Good thermal performance. Low maintenance. Many color and finish options. Don't require painting or other finishes. Moisture resistant. Less expensive than other frame types. High performance models can have insulation in cavities which increases thermal performance. Commonly made with PVC. These expand and contract with temperature variations and are even known to warp over time. Cracking in low temperatures. Color fading over time. Medium Wood High thermal performance. Attractive natural appearance. Paintable for a wide range of color and finish options. High availability and provide a traditional window look. Expensive. Expands and contracts with temperature variations. High maintenance. Very heavy. Larger profiles reduce amount of transmitted light. Older models can be drafty due to lack of weather stripping and proper flashing. High Clad Wood High thermal performance. Attractive natural appearance. Reduced exterior maintenance. Wide range of colors and finishes. Lower maintenance than wood alone. Typically these are newer models with weather stripping and proper flashing, reducing drafts. Very expensive option. Expands and contracts with temperature variations. Very heavy. Large profiles can reduce light transmission. Highest Composite Combine the performance qualities of the other types of windows. High thermal performance, low maintenance. Wide range of colors and finishes. Dimensionally stable. Increased moisture and decay resistance. Expensive to very expensive. Some use PVC. Newer product lines lack widespread availability. For vinyl components; cracking, warping and color fading. For metal components; if metal goes under sash without thermal break there is a reduction in thermal performance. High-Highest

Glazing - The choice of frame is only the first step. The majority of the surface area of a window is, of course, the glazing. There are some basic choices to make and we spell those out in the table below.

Glazing Type   Advantages Disadvantages Cost Single Glazed Currently exist in most older homes. Cheap. Very poor insulating qualities. Usually no low-e coatings. Break easily. Tendency to form leaks. Transmit sound very well. Requires the use of plastic films to increase winter performance. Low-Medium Double Glazed Increased thermal performance. Most common glazing in today's windows. Can be gas filled. Coatings and films can be applied to interior glass surfaces. Reduced sound transmission. Reduced security risk from breakage. May not perform well enough in colder climates. May require the use of plastic films to increase winter performance in colder climate regions. More expensive. Medium-High Triple Glazed High thermal performance. More surfaces for the use of coatings and films. Can be gas filled. Highly effective at reducing sound transmission. Reduced security risk from breakage. Very expensive. Heavy windows may require additional reinforcement. Diminishing rate of return (cost versus performance). High-Highest Integrated Blinds High thermal performance. Most are triple glazed applications. Low maintenance sun shading device. More surfaces for the use of coatings and films. Can be gas filled. Highly effective at reducing sound transmission. Reduced security risks from breakage. Very expensive. Heavy windows may require additional reinforcement. Diminishing rate of return (cost versus performance). Repair costs much higher due to built in technology. Highest

Other ways to make windows perform better
Other enhancements to your windows include coatings and gas fills. The most common coating used today is a Low-E, or low emissivity coating. This coating is composed of metallic oxides and can greatly reduce the solar heat gain through your windows while still allowing needed natural light into your home. Most new low-e windows apply the coating to one of the inside surfaces of the glass (in a multi-paned window), but there are options to apply low-e films to the inside of your existing windows as well. There are other coatings such as reflective films or tints that can be added to windows but these are less popular in residential applications due to a tendency to reduce the transmission of natural light. Gas fills between the panes of glass have become very popular for saving energy. Argon-filled windows are the most common, but in certain applications or for those wanting the highest performance, krypton-filled is also an option. These nontoxic, nonreactive, clear and odorless gases are injected into sealed windows and can drastically reduce the conduction of heat through the window assembly. The gases are less conductive and more viscous than regular air and prevent conduction currents between the panes of glass.

How to Choose
Whether building new or replacing your existing windows, the choice of which frame and glazing combination to go with can be very difficult. Windows represent large holes in your walls, so choosing lower performing windows can cost you a sizable sum over the life of the house. Cost will inevitably be a controlling factor when choosing windows, but if you are close, always choose to go up to the next highest performing window line. Your long-term budget will thank you.

Conclusions:
At Green3DHome.com we are fans of metal clad wood frames with triple glazing. We definitely recommend low-e coating in your windows. Buy the windows with the low-e coating between the panes because adding the film later won't give you the performance desired and it’s a real hassle. We also recommend argon-filled windows. Krypton-filled windows do perform better, but the cost versus performance isn't worth it for most applications. If you are doing a replacement of windows on an older home, especially if you currently have single glazed windows, any upgrade will have an immediate effect on your home's efficiency.