Energy Efficient Homes—Windows, PART II
Your windows may be 10% of your overall home energy loss and if you do not have a way to test your thermal envelope you may end up being another customer being taken advantage of by a good window salesperson. A blower door test will reveal how bad your windows are and how much they contribute to your energy losses and energy bills. An Energy Efficient Home Rater™ will perform a good blower door test. The results of the test will provide details concerning the amount of loss occurring through your windows and how much the installation of new windows will reduce your energy bills. The Energy Efficient Home Rater™ will also provide information about the length of time for “payback” if new windows are installed according to the level of technology built into the windows.
Windows lower the overall R-Value rating of any given wall and great strides have been taken to improve window R-Values over the past 20 years. There exists great potential for improving the use of glass as a means for gaining solar heat in a home for winter’s desired use while reflecting away such gain in the summer and at the same time increasing its R-Value against heat loss at night. It is believed that as technology continues to improve one day it will be possible to capture the best of all the desired benefits, it is only a matter of time before our needs and wants are met. At the present time the available benefits from the newly developed window technologies do not always warrant the additional costs.
How good are your present windows—Signs to look for:
· Are they tight and without drafts?
· Do you feel air movement by the windows when they are closed?
· Do your windows rattle or whistle when the wind blows?
· Do the windows have any cracks or pieces missing?
· Are they thermal windows? Thermal windows are preferable with two panes of glass with a thermal break of ¼ inch to no more than 1 inch spacing between the panes of glass.
· Are the windows made with just a single pane of glass or two (double) panes of glass?
To find out whether or not a window is made of one single pane of glass or two panes—put your hands on both sides of an open window and you will be able to feel how thick the glass is. If your hands seem to feel very close together (an1/8 of an inch or less) the window is probably a single pane of glass. If the glass seems to feel as if there is an air space between your fingers as you try to touch them together of a ¼ inch up to 1 inch then most likely the window is a thermal window. Also, if you look at the glass closely and you see a metal looking piece inside between the panes of glass it is probably a thermal window and the two panes of glass are fixed and should remain fixed. A thermal glass window R-2 has greater resistance to transferring heat and cool through it over a single pane glass window with an R-1, R-Value.
· Is the thermal window filled with argon gas?
A window with argon filled gas between two panes of glass has even a greater benefit than just air filled between two pieces of glass; and air filled between two pieces of glass is already a good insulator. Filling the gap between the glass panes with argon, a low-conductivity gas, will improve window performance by reducing conductive (“the distribution of heat or coolness through a material”) and convective (“natural: heat transferred through a medium, such as air or water, by current that result from the rising of lighter, warm air and the sinking of heavier cool air”) heat transfers. This phenomenon results from the fact that the density of the gas is greater than the density of air. The increased resistance created by argon filled gas between two panes of glass slows down the transfer of heat through the glass panes from the outside in or the inside out, depending upon the flow direction of the heat.
· Is the glass Low- e coated glass?
Low-e coating on glass was first introduced to the market two decades ago. Low-e coating, placed on the inside of the insulating glass unit, enables the sun's short-wave energy to enter the room and at the same time prevents internal warm air from leaving the room. The addition of low-e coating on glass makes the window glass an even better resister to heat transfer. Low-e coating on glass can be detected by holding a lit match up close to the window glass. If you see a reflection image of four matches it is low-e coated glass in a thermal two pane system. An easier way to find out if it is low-e coated glass is to look for a little label etched on or printed on the glass in the corners or on the thermal batten (the metal looking piece) between the two glass window panes. There are ETEKT Low-E coating detectors that when placed against glass and pressing a button can detect its presence.
· If the home you live in or want to buy has louver windows insist on having them replaced. They are almost the worst window for energy efficiency one can own.
· What are the locations of the windows? Windows at this time have a much lower
value than the surrounding wall system or ceiling windows—commonly referred to as skylights. As mentioned a single pane of glass has an R-value of R-1. A window that has two panes of glass with an air gap between them—a thermal window is R-2. A double pane thermal glass window with low-e glass coating has an R-value of R-3.5. The typical R-Value of an insulated wall is R-19.
· A step up from the louver window and single pane windows that are poorly
glazed or have no glazing, many loose fitting sashes, no weather stripping or gaskets, and no storm windows and the next worst for energy efficiency is the number of windows located on the north side of a home.
Energy Efficient Homes—Windows Part III will follow and conclude this segment on windows.
Copyright © 2006, Dennis Maq & Siti Crook, The Energy Efficient Home Team™
Windows lower the overall R-Value rating of any given wall and great strides have been taken to improve window R-Values over the past 20 years. There exists great potential for improving the use of glass as a means for gaining solar heat in a home for winter’s desired use while reflecting away such gain in the summer and at the same time increasing its R-Value against heat loss at night. It is believed that as technology continues to improve one day it will be possible to capture the best of all the desired benefits, it is only a matter of time before our needs and wants are met. At the present time the available benefits from the newly developed window technologies do not always warrant the additional costs.
How good are your present windows—Signs to look for:
· Are they tight and without drafts?
· Do you feel air movement by the windows when they are closed?
· Do your windows rattle or whistle when the wind blows?
· Do the windows have any cracks or pieces missing?
· Are they thermal windows? Thermal windows are preferable with two panes of glass with a thermal break of ¼ inch to no more than 1 inch spacing between the panes of glass.
· Are the windows made with just a single pane of glass or two (double) panes of glass?
To find out whether or not a window is made of one single pane of glass or two panes—put your hands on both sides of an open window and you will be able to feel how thick the glass is. If your hands seem to feel very close together (an1/8 of an inch or less) the window is probably a single pane of glass. If the glass seems to feel as if there is an air space between your fingers as you try to touch them together of a ¼ inch up to 1 inch then most likely the window is a thermal window. Also, if you look at the glass closely and you see a metal looking piece inside between the panes of glass it is probably a thermal window and the two panes of glass are fixed and should remain fixed. A thermal glass window R-2 has greater resistance to transferring heat and cool through it over a single pane glass window with an R-1, R-Value.
· Is the thermal window filled with argon gas?
A window with argon filled gas between two panes of glass has even a greater benefit than just air filled between two pieces of glass; and air filled between two pieces of glass is already a good insulator. Filling the gap between the glass panes with argon, a low-conductivity gas, will improve window performance by reducing conductive (“the distribution of heat or coolness through a material”) and convective (“natural: heat transferred through a medium, such as air or water, by current that result from the rising of lighter, warm air and the sinking of heavier cool air”) heat transfers. This phenomenon results from the fact that the density of the gas is greater than the density of air. The increased resistance created by argon filled gas between two panes of glass slows down the transfer of heat through the glass panes from the outside in or the inside out, depending upon the flow direction of the heat.
· Is the glass Low- e coated glass?
Low-e coating on glass was first introduced to the market two decades ago. Low-e coating, placed on the inside of the insulating glass unit, enables the sun's short-wave energy to enter the room and at the same time prevents internal warm air from leaving the room. The addition of low-e coating on glass makes the window glass an even better resister to heat transfer. Low-e coating on glass can be detected by holding a lit match up close to the window glass. If you see a reflection image of four matches it is low-e coated glass in a thermal two pane system. An easier way to find out if it is low-e coated glass is to look for a little label etched on or printed on the glass in the corners or on the thermal batten (the metal looking piece) between the two glass window panes. There are ETEKT Low-E coating detectors that when placed against glass and pressing a button can detect its presence.
· If the home you live in or want to buy has louver windows insist on having them replaced. They are almost the worst window for energy efficiency one can own.
· What are the locations of the windows? Windows at this time have a much lower
value than the surrounding wall system or ceiling windows—commonly referred to as skylights. As mentioned a single pane of glass has an R-value of R-1. A window that has two panes of glass with an air gap between them—a thermal window is R-2. A double pane thermal glass window with low-e glass coating has an R-value of R-3.5. The typical R-Value of an insulated wall is R-19.
· A step up from the louver window and single pane windows that are poorly
glazed or have no glazing, many loose fitting sashes, no weather stripping or gaskets, and no storm windows and the next worst for energy efficiency is the number of windows located on the north side of a home.
Energy Efficient Homes—Windows Part III will follow and conclude this segment on windows.
Copyright © 2006, Dennis Maq & Siti Crook, The Energy Efficient Home Team™
posted by Siti | 2:45 PM
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