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#WINDOWS R VALUE WINDOWS#
This is quite limited and your only testing the glass pack, but will allow you to test prospective replacement windows using the same methodology. Now subtract the ambient temperature from your two recorded numbers so you are left with temperature gain. You switch sides, because some low-e coatings are unidirectional and some are only applied to one plate. Wait an hour for the window to return to ambient temperature then repeat on the opposite side. Wait five minutes then turn off the lamp and quickly record the temperature of the interior glass with an IR thermometer. Place the lamp 1 inch from the exterior glass perpendicular to the window.
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Remove the sash and brace it into a standing position on a table. The stickers usually fall off vinyl windows, however, so don't get your hopes up if you've had them long.Ī simple home test can be done with a heat lamp. The most likely place you are to find a make/model number is on a sticker placed on the outer sides of a moving sash. You can check for published numbers, but they are not likely to be directly comparable to those published by other manufacturers unless your comparing recent numbers by European manufacturers. Duplicating it outside of a lab environment is impractical. Instead they are a composite number from R & U measures at several different places on the glazing system (center of glass, edge of glass, sash, frame, etc.) In Europe windows sold across member nation borders have to publish a U-value according to a predetermined formula. The U-value and R-value of glazing systems are not a single measure. In addition having a surface window treatment that reduces air circulation near the window allows the creation of a thicker boundary layer near the window, which will cool off, thus reducing the effective temperature differential between inside and outside. Having double layer window coverings can make a significant difference. In winter when it is very cold out, the radiation through the window is significant. With more clever you make the add on frames 'double pane' with plastic on both faces, turning your R-2 window into an R4 window. For a bit more you can get systems where you make frames of thin wood with magnets that stick to washers screwed to the existing frames.
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This is only a few bucks per window, adds an R to the window, and also stops air leaks around the edges of the any windows that open. Window replacement is one of the LAST steps in making a house more energy efficient.Ī much better strategy is to put shrink film plastic on the inside of your windows. While replacing the windows may not be cost effective they will make the house more comfortable. Windows such as aluminum sliders have a lower R value, often being effectively R-1. If the old window is also a serious air leak, then it has a much smaller effective R value, and a correspondingly higher cost. If I have to borrow money at even 1% the new window will never pay for itself. So the minimum payback is 133 years at zero percent interest. If the new window was PERFECT, it would save me 75 cents per year. Last year at peak winter rates, my gas bill was running $6/Gigajoule. That's about 1/8 gigajoule or about 1.25 therms. The old window: 10 square feet * 240000 degree hours/2 = 1.2 million BTUs per year. If you are in my climate you have a 10,000 degree day heating season. Suppose that you found a wonder window that was rated as R-5, and that your old windows are R-2.
#WINDOWS R VALUE INSTALL#
Suppose that the replacement window costs $100 and you install it yourself. Note that financially, replacing existing non broken windows does not pay off in terms of saving on your heating bill.Ĭonsider: Let's talk about a 1 square meter window - 10 square feet. It gets complicated enough that I have never bothered beyond the first order approximation.
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Second order approximation depends on the frame material, and to some degree on coatings, and gas fills, and years since the gas fill also depends on your heating system, exterior wind exposure. First order approximation: R-1 (british units BTU/hr/sqft/DegF) per sheet of glass.