Energy Efficient Homes—Windows PART 1
Windows play an extremely important role in a home and they have both valuable benefits and negative characteristics. Starting with the positive benefits windows are the eyes of a home. One is able to look at the outside environment through a window and see what is going on without the need to leave the comfort of one’s home. Windows make it possible to let in warm rays of sun on a cold winter’s day. They also block the wind from blowing through and they prevent insects and other unwanted creatures from coming in, plus there are many more valuable benefits.
A negative characteristic of windows is that glass is not a strong resister to temperature radiating through it. A single pane of glass has an R-Value of R-1, compared to walls that built to present day code has an R-19 Value. When you average the two, window and wall in a ratio of wall to glass it reduces your overall efficiency in keeping out the cold in winter or keeping in the cool during the summer. By placing your hand close to the window you will feel the difference. In contrast during the summer the heat comes in through the glass and is trapped in the space you are trying to keep cool, similar to that of a greenhouse effect. Both of these negative characteristics amount to a higher cost to heat and or air condition the space. A perfect thermal package for a home would be a structure without any windows or doors which of course is impractical.
Through various technologies, improvements have been made to the insulating value of glass by layering (Thermal glass), applying films (low-e coatings), and adding gas (argon). All of these positively affect the R-value and increase it to an R-2 and a maximum of an R-3.5. An R-Value of 3.5 is far greater than R-1 and it is still far from a typical wall of R-19 or higher.
The cost to raise the R-Value in glass windows increases greatly with added technologies. However, due to increases in demand and productivity manufacturers have been able to curb the cost somewhat.
Windows are an area where many manufacture’s representatives boast claims of large savings as much as 50% off your heating bill by just installing their windows. A claim for huge savings of as much as 50% applies if you have the worst case scenario for windows, such as louver widows or single pane windows that do not have storm windows over them, each pane of glass having approximately an R-Value of R-1, are poorly glazed or have no glazing, many loose fitting sashes, no weather stripping or gaskets. To replace these inefficient windows with new thermal windows or better only increases the performance of the window, roughly to an R-Value of R-2, and it does not increase the performance of the whole house in the same ratio. Claims for large savings for replacement windows may then apply but the claim is not made conditional upon the poor or good insulation qualities that may or may not be present in your home’s thermal envelope which is integral to your home’s energy consumption that determines your actual cost. If a salesperson makes a claim for great savings ask them if they will guarantee it in writing and refund your money if the windows do not save you the claimed percentage.
Bottom line—Buyer Beware!
Copyright © 2006, Dennis Maq & Siti Crook, The Energy Efficient Home Team™
A negative characteristic of windows is that glass is not a strong resister to temperature radiating through it. A single pane of glass has an R-Value of R-1, compared to walls that built to present day code has an R-19 Value. When you average the two, window and wall in a ratio of wall to glass it reduces your overall efficiency in keeping out the cold in winter or keeping in the cool during the summer. By placing your hand close to the window you will feel the difference. In contrast during the summer the heat comes in through the glass and is trapped in the space you are trying to keep cool, similar to that of a greenhouse effect. Both of these negative characteristics amount to a higher cost to heat and or air condition the space. A perfect thermal package for a home would be a structure without any windows or doors which of course is impractical.
Through various technologies, improvements have been made to the insulating value of glass by layering (Thermal glass), applying films (low-e coatings), and adding gas (argon). All of these positively affect the R-value and increase it to an R-2 and a maximum of an R-3.5. An R-Value of 3.5 is far greater than R-1 and it is still far from a typical wall of R-19 or higher.
The cost to raise the R-Value in glass windows increases greatly with added technologies. However, due to increases in demand and productivity manufacturers have been able to curb the cost somewhat.
Windows are an area where many manufacture’s representatives boast claims of large savings as much as 50% off your heating bill by just installing their windows. A claim for huge savings of as much as 50% applies if you have the worst case scenario for windows, such as louver widows or single pane windows that do not have storm windows over them, each pane of glass having approximately an R-Value of R-1, are poorly glazed or have no glazing, many loose fitting sashes, no weather stripping or gaskets. To replace these inefficient windows with new thermal windows or better only increases the performance of the window, roughly to an R-Value of R-2, and it does not increase the performance of the whole house in the same ratio. Claims for large savings for replacement windows may then apply but the claim is not made conditional upon the poor or good insulation qualities that may or may not be present in your home’s thermal envelope which is integral to your home’s energy consumption that determines your actual cost. If a salesperson makes a claim for great savings ask them if they will guarantee it in writing and refund your money if the windows do not save you the claimed percentage.
Bottom line—Buyer Beware!
Copyright © 2006, Dennis Maq & Siti Crook, The Energy Efficient Home Team™
posted by Siti | 2:43 PM
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