EGEE 102
Energy Conservation for Environmental Protection

Review and Extra Resources


Review Sheet Lesson 10 – Windows

  • Windows and Heat Loss
    • Solar radiation has infrared (IR), ultraviolet (UV), and visible waves
  • Factors in window selection
    • U factor
    • Visible Transmittance (VT)
    • Solar Heat Gain Coefficient (SHGC)
    • Air Leakage (AL)
    • Condensation Resistance (CR)
    • R = 1 / U
    • LSG = VT / SHGC
  • Shading Devices
    • Roller Shades
    • Vertical Blinds
    • Venetian Blinds
  • Window Technologies
    • Types of Glazing
      • Chemically or Physically Altered Glass (tinting)
      • Coated glass or films
        • Spectrally Selective Coatings
        • Low-e Coatings
          • Soft Coat
          • Hard Coat
          • Heat Mirror
        • After market Films
      • Multiple-layered assemblies
        • Gas Fills (argon, krypton)
        • Layers of Glass and Air Spaces
          • Single Pane
          • Double Pane
          • Multiple Pane
    • Frame and Spacer Materials
  • Smart Windows
    • Suspended Particle Devices (SPDs)
  • Heat Loss = Area x HDD x 24 / R-value

Test Yourself

The questions below are your chance to test and practice your understanding of the content covered in this lesson. In other words, you should be able to answer the following questions if you know the material that was just covered! If you have problems with any of the items, feel free to post your question on the unit message board so your classmates, and/or your instructor, can help you out!

  1. What are the main factors that are important in selecting a window?
  2. Explain briefly what technological advances account for increase in performance of windows.
  3. What are gas filled windows, and how do they perform better than regular windows?
  4. Is it true that a person in Alaska requires high SHGC of windows?
  5. If thickness of the window is doubled, what will be the new percentage heat loss?
  6. What will be the heat loss from a window if it is vacuum between two window panes?
  7. A glazing material cost about $1/ ft2 which improves the insulation by 10%. What is the payback period of adding the glazing if originally window glass cost is $10/ft2 and heat loss from window is 1000 BTU/hr. Assume the cost of heating is $10/MMBTU.
  8. A house in State College, PA consists of the following: 12 single pane windows (each 6 ft by 3 ft with an R value of 1). Calculate the total number of BTUs lost for one season through these 12 windows.  HDD for State College are 6,000.
  9. Heat loss through a window (R-2) is 10 MMBTU/year. Calculate the payback period if following filling material is used. Assume heating price to be $10/MMBTU
    Calculate Heat Loss Example
    Gas fill Additional Cost Effective R Payback period (year)
    Argon \$20 7
    Krypton \$45 12
    Xenon \$75 20

Extra Resources

For more information on topics discussed in Lesson 10, see these selected references:

  1. Office of Energy and Renewable Energy
  2. Selecting Windows for Energy Efficiency
  3. Energy Star
  4. National Fenestration Rating Council
  5. What Makes It Energy Star?
  6. Energy Technologies Area
  7. Warner, J., Selecting Windows for Energy Efficiency, Home Energy Magazine Online July/August 1995 (
  8. Efficient Windows Collaborative