E-Star: Energy Saving Calculations - Energy Savings from Replacing Windows

Energy Saving
Calculations

Energy Savings from Replacing Windows

The following calculation is designed to provide you with an estimate of the amount of money that you can expect to save by replacing old leaky windows or doors. It is extremely difficult to determine exact savings because of the difficulty in measuring actual air leakage around a given window or door. This air leakage varies tremendously due to wind velocity and direction and inside and outside air temperature. Air leakage is one of two sources of heat loss through windows and doors. The other major source is heat loss due to conduction. Conduction is related to the R-value (resistance to heat flow) of the unit.

Air leakage occurs through cracks where the window or the window or door opens, joints in the woodwork, and between the wall and the frame. Installation is critical. A poorly installed window or door may actually leak more between the wall and the frame than the existing unit being replaced.

This calculation assumes that you are replacing windows or doors of equal area. If you are decreasing the size of your windows or doors in the replacement process, you're savings will be greater. If you are increasing the size, your savings will be less. The calculations are simplified, so your actual savings could vary, but it will give you a good ball-park figure to work with.

For this calculation you will need:

Current crack length of windows or doors being replaced
Current area of windows or doors
Proposed crack length of windows or doors being replaced
Proposed area of windows or doors

Throughout the form below you will find links to supportive information you may need to help you complete the calculation. Use your Back button to return to the form.

Existing Window or Door Information
Current Leakage Rate: See accompanying table for estimated leakage rates.
Current Crack Length: For double hung windows (3 x sash width) + 2 x sash height. For others (2 x sash width) + (2 x sash height). For fixed units, crack length is 0. Add together for all windows or doors to be considered.
Current Area in Square Feet: Take width x height of all the windows or doors to be considered.
Current R-Value: See accompanying table for window or door R-values.
Proposed Window or Door Information
Proposed Leakage Rate at 25mph: See manufacturers specs.
Proposed Crack Length: Determine from unit size as above.
Proposed Unit R-Value: See manufacturers specs.
Climate and Fuel Information
Heating Degrees Days for Your Location: Heating Degree Days are a common measure of severity of heating climate. You will find the heating degree days for your location on the accompanying table.
Heating Fuel Type: Select from pull down at right
Heating Fuel Cost/Unit (enter amount in dollars): Take a recent heating bill and divide total cost by units of heating fuel consumed. If you know of a standard monthly charge, remove that from the total first.	$
Heating System Efficiency (enter amount as .xx): See accompanying table for determining your heating system efficiency.

Dollar Savings: Amount of dollars saved annually by reducing window/door leakage rates.	$

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