How To Read A Window Glass Performance Guide

How to Read Performance Guide

U Factor: (inverse of R Value)- The heat flow rate through a given construction expressed in Btu/hr/ft2/F. Values are normally given for NFRC/ASHRAE winter conditions of 0 degrees outdoor temperature, 70 degrees indoor temperature, 15 mph wind and no solar load. U-values can be expressed in terms of the glass alone (Ucog) or for the entire window (Uwindow) which includes the effect of the frame and the spacer material. The lower the number the better the insulating value.

R Value: Higher number the better

SHADING COEFFICIENT (SC) — The ratio of solar heat gain through a glazing to the solar heat gain through a single lite of 1/8″ (3.0mm) glass. Dimensionless and varying between 0 and 1, the smaller the number, the better the glazing is at preventing solar gain. The shading coefficient is specific to normal incidence angle and is being phased out in favor of the solar heat gain coefficient value. The lower the number, the less solar heat gain.

SOLAR HEAT GAIN COEFFICENT (SHGC) — The fraction of incident solar radiation which enters a building as heat. It is based on the sum of the solar energy transmittance + the inwardly flowing fraction of absorbed solar energy on all lites of the glazing. Note that the smaller the number, the better the glazing is at preventing solar heat gain. This value is preferred over the shading coefficient since it can be used for solar incidence angles other than normal to the glass surface. It can be expressed in terms of the glass alone (SHGCcog) or total unit value (SHGCwindow).

RELATIVE-HEAT GAIN (RHG) — The total amount of heat gain through a glazing system at NFRC/ASHRAE specified summer conditions, incorporating the U-value and the Solar Heat Gain Coefficient. The conditions are 230 Btu/hr/ft2, outdoor temperature of 89 degrees F, indoor temperature of 75 degrees F, and 7.5 mph wind. This value is expressed in terms of Btu/hr/ft2. The lower the number, the less heat gain.

VISIBLE LIGHT TRANSMITTANCE — In the visible spectrum (380 to 720 nanometers), the percentage of light that is transmitted through the glazing relative to the C.I.E. [Commission International de I’Eclairage (International Commission on Illumination)] standard observer. The higher the number, the more clarity of the glass.

UV TRANSMISSIONS (Tuv) — The percentage of ultra violet rays that enter a room through the glazing system. It is a predictor of potential fading damage. Lower percentages indicate less fading potential. (UV rays are those with a wavelength ranging from 0.30 to 0.38 nanometers). The lower the number the less fade potential.

LBL DAMAGE FUNCTION (Tdw-K) — This function is another way of expressing UV Transmission. It is a better predictor of potential fading damage than UV Transmission. Lower values indicate less fading potential. The LBL Damage Function is a weighted value which takes into account that as the wavelength of the UV rays get shorter, the fading damage potential increases. Therefore, two glazing systems with the same UV transmission may have different LBL Damage Function values because one allows more “shorter” wavelength rays to pass through than the other.

How To Determine Handing For Hurd Casement Windows

If you are needing to order a new operator or lock for your Hurd Casement Window you will need to determine the handing of your window as the parts are also handed.

The easiest way to go about this is:

  • Looking at your window from the inside.
  • If the LOCK for the window is on the LEFT then your window is a LEFT HAND Casement. So you would then need to order a LEFT HAND operator or a LEFT HAND Lock
  • If the LOCK for the window is on the RIGHT then your window is a RIGHT HAND Casement. So you would then need to order a RIGHT HAND operator or a RIGHT HAND Lock

To Order Hurd Window & Door Replacement Parts Go To:

How to Replace A Casement/Awning Operator For A Hurd Window

Casement Operator1. Remove the screen.

2. Remove the handle crank by pulling it straight off. (if you have a different style operator there may be a set screw)

3. Using a stiff putty knife from the inside, insert the knife between the main sill and lower sill operating stops.  Carefully pry up to remove the upper and lower sill operating stop.

4. Pry with a small screwdriver the split arm off of the sash bracket pin by prying up and off, and then pry with a small screwdriver the straight arm off the sash track shoe by prying between the arm and the track shoe downward.

5. Remove the screws that secure operator to the main sill.

6. Install the replacement operator and reverse the above removal procedure to complete.

Go to to purchase casement and awning operators.


Why Windows Seal Fail And What To Do

This is a collection of helpful information we have learn though our years of servicing many windows and information from many different window manufactures about window seal fails.

What is a seal fail?

An insulating glass unit consists of two or more sheets of glass separated by a spacer and sealant system creating a sealed airspace. A break in this seal anywhere along the edge can allow moisture between the glass panes. The actual point of failure is not usually visible because the seal is hidden inside the sash of frame. – source: Jeld Wen Windows & Doors

Unfortunately all dual insulated glass can at some point seal fail. It can look different depending on the type of glass you have. Glass can look foggy, get a purplish hue, have condensation or show spots. Here are some photos of examples of seal fails:

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What to do if you have a seal failed window:

1. Make sure that your window is not just dirty. Clean the inside and outside of your window with a damp rag. If the fog or spots are still there in the inside of the insolated unit. You will need to take the following steps:

2. Don’t panic! Rest assure that this is not an emergency situation, a seal failed glass unit is still doing its job with energy efficiency but is not aesthetically pleasing to look at and it can obstructs your view. In most cases you DO NOT have to replace the whole window. A seal failed unit does not mean that your windows are junk or that there is a manufactures defect. All glass units no matter what brand of windows you have can have a seal fail. You will either need a new sash (a sash is the glass part of the window and the wood/vinyl/mental around the glass. A sash does not include the frame of the window). Or if your window is re-glazable then you will only need a new insulated glass unit.

3. You need to determine  what Brand of window you have and if you have a warranty. A standard warranty today is 20 years on seal fails (keep in mind that if you are not the original purchaser of the windows i.e. 2nd owner of the home the warranty terms can change). In most cases it will only cover the cost of the glass and not include labor. If you windows are between 10-30 years old you may no longer have a warranty has the glass technology is always improving.

4. If you know the windowdealer you purchased the windows from call them 1st to help you with your seal fail they may have a window service department or have a recommendation. If you know what brand of windows you have in your home, you can call the window manufacture ask for customer service and they will be able to help you find a local window dealer in your area to fix your window. If you do not know what your window brand is or if they have unfortunately gone out of business you can look up a local glazer or window service technician. You can also call other local window dealers in your area and they may have a recommendation of a window service technician for you to use.

Finding the Right Widnow Servcie Technicion:

If you are using an independant window service techniction its always best to have them recommened by a window dealer. Get at least 3 bids and remember that going with the cheapest bid is not alwasy the best (you get what you pay for). Ask how long they have been servacing windows and if they have worked on your brand of window before.

If you are buying the glass you should get a new warranty on it. Ask what that warranty is, and get it in writting from the service tech and/or from the glass manufacture they are getting the glass from.

More Information:

Please click on the links below for more information we have found on seal fails and causes.

seal+failure – PDF from Jeld Wen Windows & Doors About Seal Fails, Causes and Solutions




How To Shim A Hurd Casement Window

How to shim a Hurd Casement Window –

Using Part # 183 (you can purchase shims from )

Window Shim Part # 183

  1. Crank window all the way open
  2. locate the sliver hing track screwed into the bottom of the window frame
  3. loosen the screw that is closet to the corner frame of the window
  4. Insert shim around the screw (under the hinge track)
  5. Tighten the screw
  6. this is a good time to make sure that ALL screws on the hardware are tightened so that the head of the screw is flush (DO NOT over tighten!)


This is a PDF file from hurd on how to shim a window (click on blue writing below to download).

How To Shim A Casement Window


Who Is R&R Windows & Doors

R&R Windows & Doors is an Authorized Hurd Window and Door Dealer, Parts and Service Center. One thing that sets us apart from other window and door dealers and other replacement parts websites for is that our Window and Door Experts have 50+ years combined experience with the Hurd product line. We have set up this blog to offer helpful hits and tips when replacing parts on Hurd Windows and Doors. We will also have segments with helpful information about windows and doors and any new features with Hurd Windows & Doors product line. You can visit our website at to purchase replacement window & patio door parts.