Doors and Windows - u factor in replacement windows
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Gerald Luton
03-15-05, 06:54 AM
I am in the process of installing replacement windows in my home. I was quoted .30 u factor in the sales pitch.
The windows are now at my home and the actual u factor is .32. How significant is the difference of .02?
In soil a change of one figure is measured exponentially,
that is a change from 6 to 5 is 10 times more acidic and a
change from 5 to 4 is 10 times more acidic. A change from
6 to 4 would be 100 times more acidic.
I have tried to research the difference from .30 to .32 on the internet and have had no luck finding an answer.
Could someone please help me with an answer or a web site?
Thank you,
Gerald
The windows are now at my home and the actual u factor is .32. How significant is the difference of .02?
In soil a change of one figure is measured exponentially,
that is a change from 6 to 5 is 10 times more acidic and a
change from 5 to 4 is 10 times more acidic. A change from
6 to 4 would be 100 times more acidic.
I have tried to research the difference from .30 to .32 on the internet and have had no luck finding an answer.
Could someone please help me with an answer or a web site?
Thank you,
Gerald
majakdragon
03-15-05, 07:27 AM
Gerald Luton, Welcome to thae DIY Forums.
I have included a link to a study done by the U of Minnesota and it covers all areas of the country for window U factors and their recommendations. Good luck and I hope this helps you.
http://www.efficientwindows.org/energystar.cfm
I have included a link to a study done by the U of Minnesota and it covers all areas of the country for window U factors and their recommendations. Good luck and I hope this helps you.
http://www.efficientwindows.org/energystar.cfm
XSleeper
03-15-05, 04:27 PM
Gerald,
It would be practically impossible for a salesman to tell you what the u-value of your windows will be, since the u-value changes depending on the overall glass size. I'm amazed he was within .02. I think it's misleading when salesmen do that, unless they tell you up front that it's only an estimate- or- that it's based on a window of a set size, whereas your windows will be either larger or smaller, and the value will vary, based on that.
Regarding your question, .02 is not that significant of a difference. I believe it would be correct to say that a .32 window is 2% less efficient than a .30 window. (only when the temperature inside is 70 F, and 0 F outside.) As the temperatures become closer to being the same, the difference is negligible.
U-factor (U-value) is a measure of the rate of non-solar heat loss or gain through a material or assembly. It is expressed in units of Btu/hr-sq ft-°F (W/sq m-°C). Values are normally given for NFRC/ASHRAE winter conditions of 0° F (18° C) outdoor temperature, 70° F (21° C) indoor temperature, 15 mph wind, and no solar load. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value.
For a typical residential-size window (3 by 4 feet/0.8 by 1.2 meters), changing from a standard aluminum edge to a good-quality warm edge will reduce the overall window U-factor by approximately .02 Btu/hr-sq ft-°F.
It would be practically impossible for a salesman to tell you what the u-value of your windows will be, since the u-value changes depending on the overall glass size. I'm amazed he was within .02. I think it's misleading when salesmen do that, unless they tell you up front that it's only an estimate- or- that it's based on a window of a set size, whereas your windows will be either larger or smaller, and the value will vary, based on that.
Regarding your question, .02 is not that significant of a difference. I believe it would be correct to say that a .32 window is 2% less efficient than a .30 window. (only when the temperature inside is 70 F, and 0 F outside.) As the temperatures become closer to being the same, the difference is negligible.
U-factor (U-value) is a measure of the rate of non-solar heat loss or gain through a material or assembly. It is expressed in units of Btu/hr-sq ft-°F (W/sq m-°C). Values are normally given for NFRC/ASHRAE winter conditions of 0° F (18° C) outdoor temperature, 70° F (21° C) indoor temperature, 15 mph wind, and no solar load. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value.
For a typical residential-size window (3 by 4 feet/0.8 by 1.2 meters), changing from a standard aluminum edge to a good-quality warm edge will reduce the overall window U-factor by approximately .02 Btu/hr-sq ft-°F.
Oberon
03-15-05, 06:47 PM
What he said! That was a really good reply...couldn't have said it any better.
;)
;)
Gerald Luton
03-15-05, 07:48 PM
Thank you for all of the replies. I feel better about my deal already.
Gerald
Gerald