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 Post subject: Re: Trying to decide between Alpha Windows, and Tri-State Window
PostPosted: Wed Jul 11, 2012 4:07 pm 

Joined: Wed Jul 11, 2012 11:06 am
Posts: 6
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Many Companies have Salespeople that will present there window in the best light; unfortunately and, often, unintentionally confusing the client. Therefore it's worth it for the client to come up with there core factors when evaluating a companies window. The three factors that works for me are as follows:

1: U- value
2: Design pressure value
3: Air infiltration


U- Value relates to insulation, but in an inverse proportion; in this case, the lower the number, the better the U- value. For example: Double Pane glass windows need a U-Value of .30 or lower (which is better), to qualify for the tax credit. FYI: most windows with low E glass and Argon gas, are able to meet this score so this isn't the only number to take into account.

Design Pressure rating is the score that grades the window. This score tells one how well the window drains water and how strong is the frame. Majority of windows are about a D.P 35 - 45; the higher the number, the better the frame. Also, the higher the number, the greater the pressure the window can withstand from lateral stress. For example: a window of a D.P. rating of 35 will be able to handle lateral stress of, approximately, 140mph, before failing. Alternatively, a window with a rating 65 can withstand up to 190mph. In addition, the higher the DP score, the better the window can withstand rain drainage before failing.

Air Infiltration relates to how much the window leaks in Cubic feet/minute, in a 25mph wind. These scores can be obtained from the manufacturer, through lab results and the company that markets these windows should have these figures readily available. For a window to meet the AAMA standard, the window should leak less than .30 cubic feet /minute. However, the better Double hung windows are obtaining scores of .15cfm and they're even companies that claim results of .02 cfm (but don't be afraid to ask to see this in writing.

Regarding appearance:
This is a personal preference - a good company will bring out all their samples, list the differences with their scores (u-value, D.P. rating, and Air infiltration), price it out and let you make the best choice that fits within your budget.

Good luck with your search
Kelemer Brothers/ Replacement Windows
Baltimore Md.


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 Post subject: Re: Trying to decide between Alpha Windows, and Tri-State Window
PostPosted: Wed Jul 11, 2012 5:33 pm 
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Joined: Wed Apr 04, 2007 11:21 pm
Posts: 3562
Location: DC Metropolitan Area-Maryland/Virginia/DC
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U-Factor
U-factor measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly. U-Factor ratings generally fall between 0.20 and 1.20. The insulating value is indicated by the R-value, which is the inverse of the U-value. The lower the U-value, the greater a window's resistance to heat flow and the better its insulating value.

Solar Heat Gain Coefficient
Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window, both admitted through a window, both directly transmitted, and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits

Visible Transmittance
Visible Transmittance (VT) measures how much light comes through a product. The visible transmittance is an optical property that indicates the amount of visible light transmitted. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted.

Air Leakage
Air Leakage (AL) is indicated by an air leakage rating expressed as the equivalent cubic feet of air passing through a square foot of window area (cfm/sq ft). Heat loss and gain occur by infiltration through cracks in the window assembly. The lower the AL, the less air will pass through cracks in the window assembly.

Condensation Resistance
Condensation Resistance (CR) measures the ability of a product to resist the formation of condensation on the interior surface of that product. The higher the CR rating, the better that product is at resisting condensation formation. While this rating cannot predict condensation, it can provide a credible method of comparing the potential of various products for condensation formation. CR is expressed as a number between 0 and 100.

Design Pressure = Performance Grade
The DP rating of a window or door is based on laboratory pressure testing in pounds per square foot or psf. Design pressure requirements can vary as they are based on product location on the building, height of the building, density of buildings, and wind zone designation. The positive DP number is the standard for wind blowing at the building (windward) and the negative DP number represents the vacuum pressure on the opposite side of the building (leeward).

Structural Test Pressure = 1.5 x Design Pressure
Structural is tested at 150% of DP rating. The structural rating of a window is as much about the glass as it is about the frame and sash system. In order to get a higher DP rating the window manufacturer has to consider the thickness and possible heat-strengthening (or tempering) of the glass as well as the use of higher-end hardware and good quality sealants in the frame and sash system.

STC = Sound Transmission Class
Basically, STC ratings are an established way to average how much sound is stopped by something. STC ratings are used for windows, doors, walls and most building materials. For windows, STC ratings range from 18 to 50. The STC Ratings for double paned windows usually vary from 28 to 35. Most have good air seals, but the variation is due to the glass thickness and the amount of air space between the glass. The bigger air space and thicker glass is preferred.


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