Thermal Certification



NFRC (national fenestration rating council) has taken on the responsibility of regulating the testing and certification methods for windows and doors. To achieve certification each product is computer modeled and then physically tested to verify the model. The result is a certified core product rating that can be altered depending on the glass type that is used. All of these results are available on the NFRC website for each company that participates in the program.

NFRC does have a default category of rating for unique products that have not been certified. Default rated products can be combined with certified products for an overall average rating to meet the required local ratings.


Prescriptive & Performance Methods

Prescriptive method for rating performance of the building requires that different product categories meet minimum area rating factors for full certification of the building. Depending on climate zone, prescriptive method can restrict the percentage of glass of each elevation in a building.

Performance method for the building allows an averaging of the building elements and ratings to come up with an overall factor for the building. An example would be that window and door performance can be offset with wall insulating performance. Also, less efficient windows can be combined with more efficient windows for an average to meet the required factor. The performance model allows for the best flexibility in the development of a good building energy plan.


Balanced Energy Design

For fenestration the window and door types, as well as TDL (true divided lite) and SDL (simulated divided lite) combinations, contribute to the overall balance of the ratings.

Each product type is individually tested. Swing products tend to rate better than sliding or folding products. The breakups of the glass have the largest impact. The TDL rates lower than the SDL. TDL breakups have more thermal transfer because the muntins and bars break the glass into individual pieces and the thermal mass of the muntin and the glass spacer edges produce lower efficiency. SDL divided lites give a similar appearance as TDL yet they rate better because the divided lite elements do not break up the glass. As a result the SDL has better efficiency ratings as a result.

The TDL appearance is an important design element and it also can improve overall weight of glass by having smaller square footages per lite and thinner glass pane requirements. Weighing the different advantages of each product type requires a balanced approach during the design phase of the building.

NFRC Guidelines

Since the NFRC enforcement is new to many designers, we put together a checklist to better qualify the difference between published product values and the conditions that may affect the final working value for a project.

  1. Confirm that stated values are available on all product types.
  2. Confirm that the published values are available for the grid types planned.
  3. Confirm that the glass make up used in the published values is available and not cost prohibitive.
  4. Confirm that the size of the glass does not change the glass thickness and effect the air space and the final values.
  5. Confirm that the energy performance values quoted are for the unit value and not the center of glass values. The values need to be calculated with sash, frame and NFRC rated glazing.
  6. Check the NFRC website to verify that each product type is currently rated.
  7. Combine all fenestration results and average to see what the final energy budget is.

    additional energy info:  California, Idaho, Texas, Florida, Washington, Oregon, Arizona, New York
NFRC Values

Jada Fenestration Product U-Factors and Solar Heat Gain

This chart shows a sampling of Jada NFRC U-factors and SHGC numbers for a variety of products.


Solarban 60-SDL Solarban 60-TDL SB 70/EA-SDL SB 70/EA-TDL
U-Factor
SHGC
U-Factor
SHGC
U-Factor
SHGC
U-Factor
SHGC
Direct-Set Fixed
0.34
0.34
0.46
0.30
0.27
0.22
0.40
0.20
Outswing Window
0.39
0.30
0.47
0.27
0.33
0.20
0.42
0.18
Outswing Door
0.37
0.31
0.49
0.27
0.30
0.20
0.44
0.18
Top-Hung Sliding
0.46
0.31
0.59
0.28
0.40
0.21
0.54
0.19
Bottom-Rolling
0.44
0.31
0.57
0.27
0.38
0.21
0.52
0.18

** sample glass is based on 1/8" over 1/8" insulated unit with Technoform TGI Spacer

** for a complete list of our ratings visit NFRC.org/search and lookup "Sierra Woods, Inc."

Default fenestration Product U-Factors and Solar Heat Gain

This chart shows sample U-factor and SHGC default number for a variety of products.
The NFRC site has some default table information or the Residential Compliance Manual has a full default table


Metal-thermal break
Dual Glaze
Metal- no thermal break
Dual Glaze
Metal- no thermal break
Single Glaze
U-Factor
SHGC-C or T
U-Factor
SHGC-C or T
U-Factor
SHGC-C or T
Operable Window
0.66
0.63 - 0.53
0.79
0.70 - 0.59
1.28
0.80 - 0.67
Fixed Window
0.55
0.69 - 0.57
0.71
0.73 - 0.60
1.19
0.83 - 0.68
Operable Door
0.59
0.63 - 0.53
0.77
0.70 - 0.59
1.25
0.80 - 0.67

** SHGC-C = clear glass SHGC-T =tinted glass

Energy Values
Thermal Design
glazing
Finish
Hardware
Automation
Attachment
Divided Lites
Mullions
Multi-Point
Escutcheons
Hinges & Finials
Screens
Door Sills
Safety