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Energy Conservation

It has been estimated that 20% of home heating is lost through windows, much of it through the gaps around window frames; all the rest is lost through ventilated and suspended timber floors and through open chimneys. It can be seen that under these circumstances double glazing alone cannot address the question of heat loss, and that measures to prevent air infiltration will be more effective. Even heavy curtains can be a better investment.

Wrightson, David. The Conservation and Renewal of Timber Windows, Public Information Leaflet, Cathedral Communications, Wiltshire, England [PDF file]

In some cases, owners may be concerned that an older window is less efficient in terms of energy conservation. In winter, for example, heat loss associated with an older window may make a room uncomfortable and increase heating costs. In fact, most heat loss is associated with air leakage hough gaps in an older window that are the result of a lack of maintenance, rather than loss of energy through the single pane of glass found in historic windows. Glazing compound may be cracked or missing, allowing air to move around the glass. Sash members also may have shifted, leaving a gap for heat loss.

The most cost-effective energy conservation measures for most historic windows are to replace glazing compound, repair wood members and install weather stripping. These steps will dramatically reduce heat loss while preserving historic features.
If additional energy savings are a concern, consider installing a storm window. This may be applied to the interior or the exterior of the window. It should be designed to match the historic window divisions such that the exterior appearance of the original window is not obscured.

3.0 Windows, Design Guidelines for Residential Historic Districts in Salt Lake City, Salt Lake City Historic Landmark Commission, Salt Lake City Corporation, 1999.

Benefits: Increased Light & View, Efficient Windows Collaborative, College of Architecture and Landscape Architecture, Twin Cities Campus, University of Minnesota

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