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Window Shopping


In the winter you might receive calls from telemarketing firms promoting replacement windows as a way for you to save on fuel costs.  Sure, there are some good arguments for upgrading those old wooden windows.  Maybe it’s a concern over dust from lead paint or maybe the windows are beyond any repair.  However, if your reason for upgrading is because of the telemarketers' promises of great energy savings, know that it may take quite a while for the windows to pay off in energy savings. 


Storm windows may be a more cost-effective alternative to window replacements.  They can be installed inside or outside the window and add a layer of glass to slow the heat loss, reduce energy costs and increase comfort.  Non-movable storm windows can be clipped or permanently attached to existing window frames or sashes.  Also, many older homes have storm windows that are aluminum and are permanently mounted to the exterior of wood double-hung windows.  If the storm windows are functional, why remove them?


If you considered the pros and cons and have decided it is time to get new windows, it’s important to understand some of the terminology, so that you can ask the right questions and get the best value for your money.  One thing you will quickly learn is that today's windows come in double-pane or triple-pane insulated glass, that there are a variety of styles and that they require minimum maintenance.  The most common are vinyl and aluminum clad wood windows.  Aluminum-clad wood windows have an excellent life span and low maintenance but are more expensive than vinyl.  Vinyl window frames have good thermal resistance, low cost and no maintenance, but are less durable than aluminum-clad.


What are some of the factors to consider when selecting a window?  First, realize that windows are the weak link in a home's thermal barrier.  This is because they provide two non-energy benefits: view and light.  That is why even the best windows have an insulating R value of 2-3 while the wall that supports them may have an R value of 12-20. 

Some of the other factors to consider include:


  • The U-factor.  This is a measure of heat loss.  The lower the U factor the more the window will reduce heat loss and minimize moisture condensation on the glass during cold weather.  A single pane glass starts with a U factor of 1.0.  Look for 0.35 or lower.  The most energy efficient windows will have an Energy Star logo on the label.

  • Visible Light Transmittance (VT). This is a measure of how much light passes through the window.  At 0.6 or higher the window will appear clear.

  • Condensation Resistance.  Some labels include this number which ranges between 1 and 100.  This represents how well a window resists forming condensation on the inside during cold months and on the outside during a humid summer.  The higher the number the better the window is at resisting condensation.

  • Air Leakage. Optional sticker information indicates how drafty a window is.  It measures the number of cubic feet of air per square foot of window.  A good number is between 0.1 and 0.3.

  • Design Pressure (DP).  Optional sticker information tells how well a window can withstand pressure from the wind.  It is measured in pounds per square foot.  A large window should have a DP rating of at least 30.

  • Solar Heat.  The solar heat gain coefficient (SHGC) measures the amount of the sun's heat that passes through the glazing.  For high heat gain look for .70 or higher.

  • Most new windows have a low-E which stands for low-emissivity.  This is accomplished by coating one or more panes of glass.  The coating slows down the escape of heat during the winter.  For cold climates, the low-E coating should be on the exterior surface of the interior pane.

  • Replacement vs. New. Replacement windows are designed to fit into existing window openings.  The alternative is installing a whole new window frame.  The latter makes more sense if the sill is rotting or you suspect water leaks.  Replacing windows may also involve repairing water damage to the siding or interior finish around the rough opening. 


While on the subject of windows, you may wonder why you see water condensing on your windows during cold weather.  Don't blame the windows!  They are not the problem.  They are just a cool surface delivering the message that excessive moisture is trapped inside a tight home.

Several factors affect how much condensation occurs on your windows.  For example, the higher the humidity in your home, the more condensation.  If your home's indoor humidity is too high, the first step is to determine the cause and reduce sources of moisture.  A typical family of four releases over 2.5 gallons of water/day into the air of the home.  That is almost 18 gallons per week.  Other sources include damp basements, cooking, plumbing leaks, plants and pets.  Note it only takes 4-6 pints of water to raise the humidity level for 1000 sq. ft house from 15% to 60 %.  Ways to eliminate moisture include covering bare dirt crawl space floors with plastic, correcting grading and drainage problems, venting your clothes dryer and bathrooms to the outside and ventilating the attic.

If you currently have double or triple glazed windows and note moisture between the panes, it may be an indication that the seal is broken or the desiccant filling is no longer effective.  They are now probably 85% efficient so, unless you do not like the looks of condensation between the panes of glass, why replace them?

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