Most energy audit reports place windows very low on their list of energy improvement priorities. This isn't surprising because of the relatively high cost of replacement windows coupled with what are commonly marginal improvements in their thermal performance. Since audit reports generally prioritize energy efficiency improvement opportunities according to their cost vs. thermal benefit (fuel savings) ratio, the energy payback economics of replacement windows are notoriously poor across the entire quality/cost spectrum of replacement windows. This is true because, in order to achieve significant thermal improvement with replacement windows one must invest in the very expensive triple-glazed units fitted with specialty glass and the fuel savings may not be recouped during the useful life of the window.
While all of the above mentioned cost and performance factors may be true, I believe that the listing of windows as a low priority energy improvement opportunity is fundamentally flawed, often resulting in the audit doing an unintentional disservice to the building owner. This common flaw lies in the mistaken assumption that, aside from repair and weather-sealing, window 'replacement' is the only meaningful window improvement option. I want to encourage auditors to consider the merit of many other more affordable and cost-effective window improvement opportunities.
There is more to window performance than thermal efficiency, but this site is for energy professionals so I will focus most of this blog on thermal performance. Broadly speaking, there are three ways in which windows can be thermally improved: 1) repair and weather-sealing; 2) supplemental panels and window treatments; and, 3) window replacement. As we've all learned in Energy Efficiency 101, one should undertake (or recommend) the no-cost and low-cost improvements first; and, in the case of windows, the most bang-for-the-buck lies in Category 1: repair and weather-sealing. Many energy conscious building owners will have already accomplished this with caulking. Category 2: supplemental panels and window treatments are generally the next most cost-effective category of window improvement measures. These can include: exterior storm sash, interior thermal shades, heavy curtains, and supplemental insulation panels. Of these options, exterior storms and thermal shades are most commonly found to be already in place, leaving supplemental insulation panels as a commonly overlooked but often quite affordable and highly cost-effective window improvement opportunity.
Obviously, there are those situations that demand window replacement for reasons other than thermal efficiency such as, structural integrity; but, if the existing windows are structurally sound, there are several cost effective ways to improve their performance, operation and appearance without resorting to replacement.
Future posts will address both optical and thermal window performance, as well as the human needs and expectations regarding window use, maintenance, operation and appearance.
After nearly 50 years as an architectural planning and design professional, an HVAC designer, an energy auditor and audit systems designer, a high-performance building consultant, and a residential general contractor, I narrowed my focus and sold high quality replacement windows in Northern New England for a year. This experience awakened me to the market's growing need for more affordable and cost-effective alternatives to window replacment. In response, two years ago I established Window Improvement Masters, LLC located in Orford, NH. www.windowimprovementmasters.com www.rjbacondesign.com
Though my current interests (and this blog) are focused on the role of windows in improving occupant comfort while achieving more efficient building performance; I recognize that all building systems - both static and dynamic, as well as human - must work together to satisfy the myriad needs of the building's owners and its occupants - and these needs go well beyond thermal efficiency and energy economics. I, therefore, welcome a discussion with others who appreciate the need for a holistic approach to addressing these inseparable matters of resource conservation and energy use in the built environment.