Double Glazing Guide window design guide

Window Design 

Before you can appreciate just how much a window can save you on your utility bills, you must understand the actual working of an energy efficient window.  This window replacement guide will attempt to help you in this understanding.  The theory is fairly straightforward: windows that are designed to be energy efficient are capable of slowing the heat transfer process between the inside of your house and the outdoors.  We all know that heat travels from warm to cold spaces.  In this way, the window becomes an agent of energy loss.  During the winter, the warmth of the house tends to dissipate out through the window and during the warmer season, the hot air outside tries to rush into your house via the same window as well.


Windows are central to the heat transfer process because they don’t provide good insulation as other parts of your wall assembly.  For example roofs, floors and walls are better insulated against heat loss.  The old single pane windows or inadequately installed double pane windows, or cracks on the window or frames are all prime candidates to facilitate this process.  To exacerbate the matter, even the best-sealed windows also allow some form of heat loss through the glass, as the glass is a natural conductor of heat through conduction.  This windows replacement guide will explain the technologies used to lower air flow and subsequently heat transfer.  These are the glazing technique, low-U values, low-E coatings, as well as gases like argon or krypton between panes.  As a result, these efficient windows will block the cold of winter away, while keeping you cool during the hot season.  Additionally, this guide will also deal with how to avoid the condensations formed inside the windows.  The performance indicator of an energy-efficient window is down to the construction of the window frame and a spacer material, and the object used to separate the main window glass and the individual frames of glass within the pane.


If you are serious in obtaining a FENSA certification for your household, then it is imperative for you to know that correct windows choice can enhance your qualification. FENSA accreditation is awarded based on window’s size, solar heating gain, U-factor and a host of other considerations.


Double Glazing

Glazing is the word used to define the glass in a window.  A double-glazed window describes two panes window; triple-glazed contains three. An “energy-glazed” window has a layer of lamination a gas-filled within the panes of glass. The reduction in solar gain goes is proportional to the numberamount[/size] of glazing.

If the solar gain is overly high, carpet, furniture and floors tend to fade easily and you need more energy for cooling to offset the solar gain; still, a decent amount of solar gain is necessary to counter the cold of winter. A double-glazed can trigger a 10 percent reduction in solar gain; triple-glazing by 20 percent. This windows replacement guide urges that households with single-glazed or single-pane windows upgrade to double- or triple-glazed windows. It will make a world of difference for your utility bills.



Low-emissivity (low-E) coating also restricts the amount of energy transfer through the window. This coating is a transparent lamination that applies itself to the window pane directly. It can be coated on either the inside surfaces (surfaces on opposing ends) or the exterior. Low-E coatings facilitate passing through of sunlight but can cut down the heat transfer process via the window glass. In addition, businesses have also made available low-E squared and low-E cubed, which are effectively the extensions of low-E coatings and denotes two or three layers of coatings of low-E respectively.

There are two variations of low-E coatings, i.e. soft and hard types. Soft-coat low-E is comparatively not as robust and it can disintegrate under prolonged exposure to moisture and air. Conversely, while hard low-E coatings are able to withstand harsher conditions, their energy efficiencies are not comparable to those of soft coatings.

As per guideline provided by U.S. Department of Energy, low-E coated (both soft and hard variations) windows are typically priced around 10% – 15% more than conventional windows, which more than compensate the 30 to 50 percent enhancement in energy loss reduction. Low-E coated windows have come a long way from its early days of make-to-order status to become standard on windows.


As pointed out earlier in this windows guide, R-value defines the efficiency of insulation of ceilings, walls, etc.; its reading is in direct relationship with the extent or effectiveness of the insulation. However, it is not practical to use R-value alone to measure windows insulation. They are different in the sense that they are subject to several external factors, such as wind, rain, sunlight, inside and outside air temperatures, just to name some of them. It is only natural that a different measurement system is applied on to windows.

This measurement system is called U-value, also known as U-factor. The U-value here is a more useful calculation of heat loss via the window, or heat transfer. (R-values may still be listed on windows on sales, but the values have no real significance as they are just readings on the center portion of the window, thus not an accurate measurement for the entire window.) When one is referring to U-value, the lower the reading, the higher the energy efficiency is. In cold weathers, U-value of .35 or lower is preferred.

Windows with multi-glazing and have krypton or argon filled are also effective in reducing heat loss and generally have low U-values.


Solar Heat Gain Coefficient(SHGC)

The SHGC is an indicator used to measure how well solar radiation is blocked from the sun. Lower reading of SHGC means less solar heat is transmitted across. The ENERGY STAR program includes guidelines and criteria for doors and windows for three climate zones in the UK Manufacturers would be in a better position to tell if the product is ENERGY STAR–certified or not. For ENERGY STAR certification criteria, all products are required to be rated, certified, and labelled for both SHGC as well as U-value according to the procedures of the NFRC (or short for National Fenestration Rating Council) or able to satisfy the ENERGY STAR qualification criteria in at least one of the climate zones.