Build It Green

Window Efficiency Model

Warm Weather

Cold Weather

How do single- and double-pane windows affect energy efficiency?

First, select a single-pane window.

Next, click the play button on the graph to watch HVAC energy use over a school day. Notice how the window type affects HVAC energy use. Record your results.

Repeat these steps with a double-pane window and record your results.

Finally, compare how much energy a building uses when it has a single-pane versus a double-pane window.

Use the arrows to think about energy transfer

The yellow arrows represent how solar radiation from the sun interacts with a window. Zoom in to see how different window types reflect, absorb, and transmit solar radiation.

The red arrows represent the energy transfer from warmer to cooler spaces. In warm weather, the warmer space is outside the building, which means that energy transfers from outside to inside the building.

The red arrows represent the energy transfer from warmer to cooler spaces. In cold weather, the warmer space is inside the building, which means that energy transfers from inside to outside the building.

Room Temp
Set to
Solar radiation Total energy flow

Window Type

HVAC Energy Consumption Over School Day

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Cumulative HVAC Energy Use 0 kwh

About the Data

The data for this interactive uses average transmission, absorption, and reflection percentages for a typical pane or double-pane of glass to represent the dispersal of solar radiation when it interacts with glass. Actual amounts vary depending on the quality of the glass and whether there are any special glazings or blemishes that would affect reflection, absorption, or transmission.

The data to represent energy transfer is intended to represent conceptual ideas for how solar radiation interacts with glass, and also the spontaneous transfer of energy from hotter to colder regions. The actual amount of energy transfer in and out of a building would depend on the quality of all the materials used to insulate the building.

The amount of energy used by an HVAC system would depend on the type and efficiency of the system. This interactive uses average materials and HVAC run times to simulate the system.