Question about New Windows I Just Bought
#1
10-20-05, 11:05 AM
Question about New Windows I Just Bought
Hi,
I just received 13 double hung Xact brand windows today and I wanted to know 2 things... First, are a U Factor of .33, a solar heat gain coefficient of .29, and visible transmittance of .46 good numbers? I know its a little late to ask now but I just wanted to see if they are good efficiency ratings.
Second, some of the windows I received are missing a chunk from the nailing fins on the corners. The glass and everything else looks fine, just the very corner where the top and side nailing fins join, a little piece is missing. I kind of figure that this might be common because its just a nailing fin. But since this is the first time I received a bulk order of windows, I wanted to make sure I should not call the retailer and complain.
I just received 13 double hung Xact brand windows today and I wanted to know 2 things... First, are a U Factor of .33, a solar heat gain coefficient of .29, and visible transmittance of .46 good numbers? I know its a little late to ask now but I just wanted to see if they are good efficiency ratings.
Second, some of the windows I received are missing a chunk from the nailing fins on the corners. The glass and everything else looks fine, just the very corner where the top and side nailing fins join, a little piece is missing. I kind of figure that this might be common because its just a nailing fin. But since this is the first time I received a bulk order of windows, I wanted to make sure I should not call the retailer and complain.
#2
10-20-05, 09:09 PM
windows
Those numbers are fine. They would be code-acceptable anywhere in the country.
The transmission seems a bit low, so I am guessing that you might have a tinted LowE coating? That would explain the lower number, but I would be surprised to see a tinted LowE in your part of the country...
The transmission seems a bit low, so I am guessing that you might have a tinted LowE coating? That would explain the lower number, but I would be surprised to see a tinted LowE in your part of the country...
#3
10-21-05, 05:50 AM
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Pete,
The efficiency ratings of the glazing is only part of the overall efficiency.
Air infiltration through the jambs, sill area and top of window should also be considered. Most manufacturers do not list this value on the window because the ratings are for the glazing only. But a search on the manufacturers website may give the value on air infiltration. This is just as important as the ratings you see pasted on the window. The "Pella" company uses a wind speed of 50 mph against their double hung windows and the value for air infiltration at that speed is 0.30 cfm. So use both the wind speed and air infiltration as a guide.
The efficiency ratings of the glazing is only part of the overall efficiency.
Air infiltration through the jambs, sill area and top of window should also be considered. Most manufacturers do not list this value on the window because the ratings are for the glazing only. But a search on the manufacturers website may give the value on air infiltration. This is just as important as the ratings you see pasted on the window. The "Pella" company uses a wind speed of 50 mph against their double hung windows and the value for air infiltration at that speed is 0.30 cfm. So use both the wind speed and air infiltration as a guide.
#4
10-28-05, 07:35 AM
Thanks rjordan, I never even realized that. I thought the numbers were for the entire window, as it sits installed properly.
Oberon, I did get the LowE glass and argon gas filled. But they're not tinted lowE. If the transmission is low, does that mean that they're more efficient in summer but less in the winter? Or are they equally efficient during all seasons? Just curious what you meant by that.
Oberon, I did get the LowE glass and argon gas filled. But they're not tinted lowE. If the transmission is low, does that mean that they're more efficient in summer but less in the winter? Or are they equally efficient during all seasons? Just curious what you meant by that.
#5
10-30-05, 02:24 AM
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Pete,
The way I understand it, the efficiency of the window glazing is based on a certain percentage of rejection of solar heat in summer and the reflection of interior heat in winter. Window manufacturers design their windows to meet certain criteria depending on what part of the country they will be installed; at least the reputable one's do. So yes, the efficiency percentage will stay the same but the rating results will be most likely miminal as weather conditions change.
The way I understand it, the efficiency of the window glazing is based on a certain percentage of rejection of solar heat in summer and the reflection of interior heat in winter. Window manufacturers design their windows to meet certain criteria depending on what part of the country they will be installed; at least the reputable one's do. So yes, the efficiency percentage will stay the same but the rating results will be most likely miminal as weather conditions change.
#6
10-30-05, 07:50 AM
LowE
Pete,
Tinted LowE is used primarily in situations where you need to block sun-glare and excessive solar energy gain.
Generally, I would expect a non-tinted LowE to have a visible transmittance in the 60%(+) range, with 70% VT very common. That is why I was curious if you had a tinted LowE which often has VT in the 38% to 48% range...thus your 46% falls in that area.
As jordan said, LowE coatings can be very climate specific. As a general rule, consider that there are two types of LowE coatings - not including specialty products such as tinted LowE.
In simplest terms, all LowE coatings block heat...that is what they are designed to do. But, it isn't quite that simple.
High Solar Heat Gain (HSHG) coatings will block the heat in your home from going outside in winter, but they will do very little to block direct solar energy gain from coming into your house. Now most people in the north consider this to be a very good thing because folks LIKE that solar heat gain in the winter. But, that same window will also allow solar heat gain in summer as well and that is certainly not an advantage.
So, if you want to use a HSHG product, then it is a good idea to make allowances for the summer solar gain as well. One method is awnings to keep the windows in the shade - in the summer - when the sun is high over head. Or, if someone is building, then they can incorporate a bigger soffit to shade the windows in summer and still be able to take advantage of the lower sun in winter.
Low Solar Heat Gain (LSHG) is specifically formulated to block solar heat gain. This coating is very popular in the south where solar heat gain in summer is a significant problem that is not offset by the advantage of gain in the winter. This coating blocks a great deal of the summer heat and helps lower TOTAL home energy usage by 35% or better (actual measured numbers in field testing) depending on your location, when compared with non-LowE coated products.
Your .29 SHGC and VT both indicate a LSHG product.
Tinted LowE is used primarily in situations where you need to block sun-glare and excessive solar energy gain.
Generally, I would expect a non-tinted LowE to have a visible transmittance in the 60%(+) range, with 70% VT very common. That is why I was curious if you had a tinted LowE which often has VT in the 38% to 48% range...thus your 46% falls in that area.
As jordan said, LowE coatings can be very climate specific. As a general rule, consider that there are two types of LowE coatings - not including specialty products such as tinted LowE.
In simplest terms, all LowE coatings block heat...that is what they are designed to do. But, it isn't quite that simple.
High Solar Heat Gain (HSHG) coatings will block the heat in your home from going outside in winter, but they will do very little to block direct solar energy gain from coming into your house. Now most people in the north consider this to be a very good thing because folks LIKE that solar heat gain in the winter. But, that same window will also allow solar heat gain in summer as well and that is certainly not an advantage.
So, if you want to use a HSHG product, then it is a good idea to make allowances for the summer solar gain as well. One method is awnings to keep the windows in the shade - in the summer - when the sun is high over head. Or, if someone is building, then they can incorporate a bigger soffit to shade the windows in summer and still be able to take advantage of the lower sun in winter.
Low Solar Heat Gain (LSHG) is specifically formulated to block solar heat gain. This coating is very popular in the south where solar heat gain in summer is a significant problem that is not offset by the advantage of gain in the winter. This coating blocks a great deal of the summer heat and helps lower TOTAL home energy usage by 35% or better (actual measured numbers in field testing) depending on your location, when compared with non-LowE coated products.
Your .29 SHGC and VT both indicate a LSHG product.
#7
11-01-05, 02:31 PM
Well, thanks again Oberon and Rjordan. That was very informative. Not exactly much I can do at this point since I already have the windows, but at least I know a little more about them and how they relate to my home's energy. Certainly much of that information is news to me and I'll be better advise to all future purchases or friends!
