Double Pane Replacement Windows

Double pane windows are actually two pieces of glass with a space (typically 1/2″ to 3/4″) between them (double paned windows are often referred to as double glazed windows). Double pane windows are popular for their energy efficiency and their sound reduction properties.

The key to dual pane windows is the space between the panes of glass. Glass conducts heat very and by adding a space between the pieces of glass a window becomes much more energy efficient.

Think of how hot the outside of a coffee mug gets when you pour hot coffee in it. If you pour that same hot coffee into a thermos you would feel very little, if any, warmth on the outside of the thermos.

A thermos works the same way double paned windows, they have an air space between the inside liner and the exterior. The same holds true with a cold drink.

To increase the performance of double pane energy efficient windows the space between the panes can be further insulated by filling it with Argon gas or Krypton gas and the inside of the glass panes can be coated with Low-E coating.

Triple pane windows, which have three pieces of glass and two air spaces, and quad paned windows are also available.

Benefits of double pane windows

  1. More energy efficient
  2. Reduce outside noise
  3. Reduce UV rays (if window has Low-E coating)

How double pane windows work

The object of a window, aside from keeping wind and rain out, is to reduce the amount of heat gain and heat loss for a home, depending on the season. Heat (and cold) can be transmitted through the glass (rememberĀ  the thermos example) and the window sash (the material that holds the glass and is inserted into the window opening) and the frame/seals so the ultimate energy efficiency of a window depends on more than just the glass.

Heat transmission

The U-Factor of a window measures the rate of heat transfer and indicates how well a window insulates. The lower the U-factor, the better the window insulates. Dual pane windows have a much lower U Factor than single pane windows.

Adding Argon or Krypton gas further reduces the U Factor of a window. The U Factor of a window is important for all windows, not just windows that receive direct sun

Solar gain

Windows that receive direct sun can transmit considerable radiation heat through the glass and sash. This is referred to Solar Heat Gain and can account for up to 30% of air conditioning costs. The Solar Heat Gain Coefficient (SHGC) of a window measures the amount of solar energy transmitted through a window.

Adding Low-E coating to a window can dramatically reduce solar heat gain and give a window a lower SHGC score. The lower the SHGC, the less solar heat the window transmits. The SHGC is most important for windows that receive direct sunlight.

Window ratings

The National Fenestration Rating Council (NFRC) rates windows in five categories but U-Factor and Solar Heat Gain Coefficient are the only ones used by the Energy Star Window Program to determine Energy Star Qualified Windows. All NFRC rated windows will have an Energy Star label on them making it easy to compare windows.

Low-E double pane windows

Low Emittance (Low-E) coating is an invisible metal or metallic oxide layer which coats a window pane. Low-E coatings reduce the amount of heat that is transferred through (in and out) the glass. Low-E coatings also reduce the ultraviolet (UV) light which passes through the window which causes fading of flooring, furniture, artwork, photographs and window coverings.

Low-E coatings are particularly effective in multi-pane window designs, especially when all panes have been coated. Low-E coatings are available in high, moderate and low solar gain.

Low-E windows are typically 10-15% more expensive but the U.S. Department of Energy estimates that Low-E coatings can “reduce energy loss by as much as 30-50%.”

Argon / Krypton gas windows

Filling the space between the panes of glass with Argon or Krypton gas increases the energy efficiency of a window. The gasses are heavier than air and make it more difficult for heat to pass through. Both gases are non-toxic, clear and odorless.

Argon gas requires an approximately 1/2″ space between panes of glass and Krypton requires 3/8″. Krypton gas allows less heat to pass through but is more expensive.

How much will you save with double pane replacement windows?

double pane replacement window

The energy efficiency of a window is determined by more than just the glass. The sash (the material that holds the glass and is inserted into the window opening) and the frame/seals also affect how energy efficient a window is.

So your ultimate savings will be depend on the sash you choose and how the windows are installed.

The U.S. Government estimates that the average home will save between $125 and $465 per year by replacing single pane windows with double pane windows. Savings vary based on where the home is located, the windows orientation to the sun and the amount of shade it receives.

In most instances the savings on utility bills offsets the cost of double pane replacement windows in 3 to 8 years.

Types of double paned windows

Dual paned windows are available in many styles, including:

  • Double hung
  • Single hung
  • Casement
  • Sliding
  • Bay

Dual pane windows are also available in a variety of sash materials, including:

  • Wood
  • Vinyl
  • Aluminum
  • Wood clad
  • Composite

Vinyl double pane windows are one of the most popular replacement windows because of their reasonable price, low maintenance and durability. You can also get double glazed storm windows as well as doors including sliding doors and patio doors.

Low-E double pane windows

Low Emittance (Low-E) coating is an invisible metal or metallic oxide layer which coats a window pane. Low-E coatings reduce the amount of heat that is transferred through (in and out) the glass. Low-E coatings also reduce the ultraviolet (UV) light which passes through the window which causes fading of flooring, furniture, artwork, photographs and window coverings.

Low-E coatings are particularly effective in multi-pane window designs, especially when all panes have been coated. Low-E coatings are available in high, moderate and low solar gain.

Low-E windows are typically 10-15% more expensive but the U.S. Department of Energy estimates that Low-E coatings can “reduce energy loss by as much as 30-50%.”

Argon / Krypton gas windows

Filling the space between the panes of glass with Argon or Krypton gas increases the energy efficiency of a window. The gasses are heavier than air and make it more difficult for heat to pass through. Both gases are non-toxic, clear and odorless.

Argon gas requires an approximately 1/2″ space between panes of glass and Krypton requires 3/8″. Krypton gas allows less heat to pass through but is more expensive.

Replacing & Installing double pane windows

Installing double pane windows is no different than any other type of windows. If you are replacing single pane windows with double pane windows the new windows will most likely be thicker than the windows you are replacing which may require window jams to be moved or the window opening to be modified to accommodate the thicker window.

Cleaning your new double pane windows is no different than other windows. In fact, many new windows allow you flip the window around while it is still in the frame to let you clean the outside glass from inside your home. This is especially helpful for second story windows.

You do not need to clean the sides of the glass that face each other. If these sides of the glass need cleaning it most likely means there is a leak between the panes which means you are not getting the maximum energy efficiency from the window.

Repairing double pane windows

If both panes of glass on a double pane window are broken you will need to replace section of the window. If you have Low-E windows be sure the replacement glassĀ  has the same Low-E coating. Some double pane windows have been sealed at the factory to prevent dust and condensation from getting between them.

In these types of windows you cannot just replace just one pane since you will no longer have a proper seal which will decrease its energy efficiency.

If one pane of dual pane Argon or Krypton Gas windows breaks you will have to replace the entire section of the window since the gas is added at the factory.