Interior Storm Windows
Window: With Interior Storm Window vs. Conventional
Interior glazing that roughly doubles the insulation value of single-pane windows and can greatly decrease infiltration from leaky windows while not impacting the building's appearance. It is often color-matched to minimize impact on a building’s interior appearance.
Synopsis:
Interior storm windows are an alternative to exterior storm windows and window replacement, with similar energy benefits. They are easy to install and well suited to do-it-yourself (DIY) projects. They have minimal impact on the appearance of the existing windows, making them an ideal retrofit for attractive old windows and historical buildings. They also decrease noise from the outside by up to 50% compared to a single-pane window and generally offer better sound performance than a new double pane window. The storm windows are custom cut for each window. They are typically held in place by a compression fit (a gasket on the edges that compresses a bit against the window frame) or a magnet in the frame that attaches to metal fittings installed on the window sill or frame. Several types of glazing are offered by different manufacturers including standard and low-e glass, acrylic, and optical grade polyvinyl. The storm windows can be a single fixed pane, multiple side-by-side panes, or sliders. Fixed pane interior storm windows can be removed during mild weather to allow for window operation, but they should be handled and stored carefully.
The tight seal of the interior storm window effectively cuts cold and hot drafts from outside and keeps warm, moist interior air from condensing on the cool window panes in winter, which helps to minimize deterioration of the window frame over time. The insulation value of a single-pane window with a low-e interior storm window is comparable to the U-value of a standard double-pane replacement window (0.41 over single pane aluminum and 0.34 over single pane wood versus 0.35 for standard double pane). Interior storm windows over existing single and double pane windows tended to have 5% to 10% better U-values than exterior storm windows (Culp, et. al. , null Pg Table 3.1 and 3.2). Estimates by several studies of heating and cooling energy savings from interior storm windows ranged 10% to 30% depending on the application.
The cost for interior storm windows vary from less than $10/sqft to over $20/sqft. These costs are comparable (particularly at the upper end) to vinyl double-pane replacement windows, but are much less than higher end wood window replacements. Exterior storm windows are generally less expensive than interior storm windows (less than $10/sqft). Installation costs for interior storm windows are less than costs for replacement windows or exterior storm windows. There are DIY kits and videos for making your own interior storm windows that offer a less expensive option.
Energy Savings: 40%
Energy Savings Rating: Extensive Assessment
What's this?
| Level | Status | Description |
| 1 | Concept not validated | Claims of energy savings may not be credible due to lack of documentation or validation by unbiased experts. |
| 2 | Concept validated: | An unbiased expert has validated efficiency concepts through technical review and calculations based on engineering principles. |
| 3 | Limited assessment | An unbiased expert has measured technology characteristics and factors of energy use through one or more tests in typical applications with a clear baseline. |
| 4 | Extensive assessment | Additional testing in relevant applications and environments has increased knowledge of performance across a broad range of products, applications, and system conditions. |
| 5 | Comprehensive analysis | Results of lab and field tests have been used to develop methods for reliable prediction of performance across the range of intended applications. |
| 6 | Approved measure | Protocols for technology application are established and approved. |
Simple Payback is one tool used to estimate the cost-effectiveness of a proposed investment, such as the investment in an energy efficient technology. Simple payback indicates how many years it will take for the initial investment to "pay itself back." The basic formula for calculating a simple payback is:
Simple Payback = Incremental First Cost / Annual Savings
The Incremental Cost is determined by subtracting the Baseline First Cost from the Measure First Cost.
For New Construction, the Baseline First Cost is the cost to purchase the standard practice technology. The Measure First Cost is the cost of the alternative, more energy efficienct technology. Installation costs are not included, as it is assumed that installation costs are approximately the same for the Baseline and the Emerging Technology.
For Retrofit scenarios, the Baseline First Cost is $0, since the baseline scenario is to leave the existing equipment in place. The Emerging Technology First Cost is the Measure First Cost plus Installation Cost (the cost of the replacement technology, plus the labor cost to install it). Retrofit scenarios generally have a higher First Cost and longer Simple Paybacks than New Construction scenarios.
Simple Paybacks are called "simple" because they do not include details such as the time value of money or inflation, and often do not include operations and maintenance (O&M) costs or end-of-life disposal costs. However, they can still provide a powerful tool for a quick assessment of a proposed measure. These paybacks are rough estimates based upon best available data, and should be treated with caution. For major financial decisions, it is suggested that a full Lifecycle Cost Analysis be performed which includes the unique details of your situation.
The energy savings estimates are based upon an electric rate of $.09/kWh, and are calculated by comparing the range of estimated energy savings to the baseline energy use. For most technologies, this results in "Typical," "Fast" and "Slow" payback estimates, corresponding with the "Typical," "High" and "Low" estimates of energy savings, respectively.