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Replace Windows

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  rev. 2008-11-25        

Existing Conditions

There are single pane windows in several areas of the facility.  Glass has very little thermal resistance, so the windows represent a major area of heat loss in winter and heat gain in summer.  In addition, the existing frames and operable sections are leaky, so there is significant air infiltration around them.

Retrofit Conditions

It is recommended that the single pane windows be replaced with double pane vinyl [thermally broken aluminum] frame windows.  Existing operable windows should be replaced with operable windows.  Newer windows will have a higher R-value (better insulating characteristics), and will also have tighter frames resulting in less infiltration.  Specify argon-filled windows with a low-emissivity interior coating to block some of the summer radiant heat gain and to reduce color fading of furniture or carpets.

Further Benefits

Occupant comfort is enhanced with lower radiant heat losses from the windows in winter, and less intense solar gain in the summer.

Application Details

Install high-efficiency windows.

For greatest air conditioning savings, in commercial applications, consider tinted glass with high shading coefficients.  If natural daylighting of perimeter areas is an objective, consider leaving an upper panel without tint.  The untinted panel should be frosted to reduce glare on computer monitors.

Issues and Concerns

Window replacement has a long payback when considered strictly in terms of energy conservation.  It is usually undertaken as building renewal, with the incremental cost of better windows justified on energy savings.


This recommendation is in accordance with Measure BE12 of the CMHC manual on Energy and Water Efficiency in Multi-Unit Residential Buildings.



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