Extension and Ag Research News


Look at Options Before Replacing Windows for Energy Savings

Window replacement may not be the best option.

Whether the glare of the summer sun or the chill of winter winds is the problem, inefficient windows can affect the energy bills of a home or business. But going shopping for windows might not be necessary just yet.

“Replacing windows is an expensive process,” says Ken Hellevang, a North Dakota State University Extension Service agricultural engineer. “Look at how much you’re going to spend on the windows. If it’s strictly heat loss that you’re experiencing, how much difference will it make? How long will it take to pay for the windows with the amount being saved?

“It’s difficult to justify replacing windows based just on the conductive heat loss,” he adds. “If you’ve got air leakage around the window or rotting wood, then you could go ahead and make the switch, but realize it’s going to take a long time to get a payback.”

Here are some budget-saving ideas that will improve existing windows:

Add a Tint

Tinting windows keeps materials from fading, reduces sun glare on computers and keeps the sun’s rays from warming certain areas of a building when the rest of it is comfortable, says Russ Schell, owner of RJ Energy Solutions of Fargo. He advises small businesses and homeowners about more energy-efficient practices.

He points to one business with 126 south-facing windows that applied a film on the inside of the windows to reduce air-conditioning costs in the summer.

“When that sun was coming in, they used their building air conditioning, plus they had stand-alone units in their offices trying to overcome that heat coming through those windows,” he says.

Air conditioning was operating even when the temperature outside was 55 degrees due to the sun’s heat beaming through the windows.

Now, window tinting keeps the mechanical cooling off until the outdoor air temperature is at the point where mechanical cooling actually is needed.

Businesses and homes should consider window tinting when air conditioners are operating and outside temperatures are still relatively cool or when some other discomfort exists, Hellevang says.

Control Condensation

Condensation on windows occurs when air inside the house touches the cold surface of the windows and turns into condensation.

“That problem can be solved either by warming the window surface or lowering the humidity,” Hellevang says.

Keep the inside humidity level below 40 percent during the winter, he advises. An air exchanger will help with the overall air quality inside a building and control humidity. More information about window condensation and controlling indoor humidity can be found in an NDSU publication titled “Keep Your Home Healthy.” It is available at https://www.ag.ndsu.edu/pubs/ageng/structu/ae1204.pdf.

Another publication, “Air-to-Air Heat Exchangers for Healthier Energy-efficient Homes,” describes ways to control moisture levels inside a building and provide the desired ventilation to retain indoor air quality while saving energy. It is available at http://www.ag.ndsu.edu/pubs/ageng/structu/ae1393.pdf.

The window surface can be warmed by increasing the window insulation value and reducing cold air coming through the window and cooling the glass surface. If your windows are cold, one good option for warming the glass surface is to place a plastic window film over the window with an air space between the plastic and window. A wide variety of window films that will reduce heat leaks and air infiltration around windows is available.

Window films also can remedy the drafty feeling from convection currents that are caused as warm air from a home comes into contact with the cold window. The air drops and more warm air from the home replaces it.

This continuous cycle can cause the cold, drafty feeling next to a window, even though no air may be leaking through the window from outside. Window films create an air pocket between the window and the film, helping keep the window warmer.

Add Extra Coverings

Insulated window treatments are another way to save a few dollars on heating and cooling bills.

Installed properly, window coverings can reduce heat loss significantly. The advantage of the window treatments is that they can be opened on the sunny side of the house to allow the sun to add free heat to the home. In the evening when the sun goes down, simply shutting the blinds retains the heat.

Window treatments also can aid in reducing heat gain during the summer. Close the covering when the sunshine is coming through the window.

Deciding to Replace

Single-pane windows, rotting wooden frames and leaking window seals are indications that windows should be replaced, Schell says.

“That’s when a window is inefficient and costing a lot of money,” he says.

But consider all your options first.

“Replacing the windows may be the correct choice, but sometimes there are other options, such as caulking and weather stripping to reduce infiltration, that you should consider when making a decision,” Hellevang says.

If replacing a window, select one rated by the National Fenestration Rating Council. The rating will list the following factors that should be considered when selecting a window:

  • U-factor measures the rate of heat transfer from inside a room. The lower the number, the lower the potential for wasted heating expenses.
  • Visible transmittance measures how much natural light can come into a room. A high number means more natural light.
  • Solar heat gain coefficient measures the amount of outdoor solar radiation heat that can enter a room. The lower the number, the lower the potential for wasted cooling expenses.
  • Air leakage measures how much air will enter a room through the window. The lower the number, the lower the potential for draft through the window.

NDSU Agriculture Communication - May 31, 2016

Source:Ken Hellevang, 701-231-7243, kenneth.hellevang@ndsu.edu
Editor:Luann Dart, 701-584-2172, luann@westriv.com
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