Energy Efficient Windows
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Deciding how to incorporate energy efficient windows in any room during home renovation can be a big decision, and your energy audit will help you make an energy-wise decision.  If the windows in the room or rooms are fairly new and the frames are in good shape, you may decide to opt for placing energy efficient films on the inside of the windows rather than replacing the entire window, which can very often be pretty expensive.

However, if you will be pretty much “stripping” the inside of the walls down to the studs so you can add insulation, this makes it quite easy to replace the windows with new energy efficient windows like Low-E single or double insulated energy efficient windows are very good at saving energy by isolating the outside ambient temperature from the inside temperature, but has much less effect on the transmission of radiant solar energy to the interior of the house. However, new Low-E glass blocks a certain amount of radiant energy as well as ultraviolet light.  Make sure your select the best energy efficient windows for your climate and exposure – will cold rejection or shielding from sunlight be more important? Energy saving tax incentives and product rebates may also bring the cost of replacing the windows to a level that fits your budget, especially when you consider the long term energy cost savings the new windows will bring to your utility bills.

On the other side, if your planned renovation is on a smaller scale, adding a window film on the inside of your existing windows can create energy efficient windows and provide a lot of ultra-violet (UV – the sun’s damaging rays) protection and also can stop a lot of the sun’s radiant heat producing rays.  In addition to being less expensive, it is also faster to install.  When you are looking at film treatments for your windows, you’ll want products that do not color or darken the room.

As you look at possibly adding an energy saving window film to create energy efficient windows, there are two major types from which to choose: dye based films that absorb heat and have additives to block UV (color fading and furniture damaging) rays, and metalized films that reflect heat back outside and block the UV rays.

Many window films have numbers in the range of 30 – 70 as part of their name.  This tells you how much light is transmitted through the film, 30% – 70% in this case.  If a film only transmits 70% of the light, it will definitely block the sun’s rays, but the room will be very dark, even during the day, but especially at night.  On the other hand, films that only transmits 30% will leave the room much lighter, but also allow in more of the sun’s light – possibly more than you want.

Manufacturers and installers of energy efficient windows should work with you to recommend the best type of film for your needs, and possibly even offer sample swatches for you to test.  You will probably find some difference between 50% from manufacturer A and 50% from manufacturer B.  Just select the one that is right for you.

Here are some of the terms you may run across as you are researching films for your windows:

VTL – Visible Light Transmission; just remember, higher numbers pass more light for a brighter room

UVR – Ultraviolet Light Rejection; how much furniture and color damaging UV light the film does NOT allow to pass.  You will want to look for a the highest number you can get here to protect your valuable furniture and artwork.

SC – Shading Coefficient; how well the film or coating actually blocks solar energy.  You are looking for low numbers here for the most efficient “shading.”

SHGC – Solar Heat Gain Coefficient; compares the amount of sunlight entering the room with the amount of sunlight striking the window.  Again, low numbers are desirable.

TSER – Total Solar Energy Rejected; the amount of solar heat rejected or blocked by the film.  Here, a higher number will result in a cooler room.

TSOL – Total Solar Transmittance; as you might expect, this is how much solar heat passes through the film into your room.

TSA – Total Solar Absorptance; how much solar heat is actually absorbed by the film.  Since this heats the film, it will also heat the room.  Blocking the heat is better than absorbing.

U-Value – overall coefficient of heat transferred to the room by conduction.  Similar to its opposite, R-Value (as in the insulation in your walls and attic).  However, unlike R-Value, a lower number is desirable.

Emissivity; how well a film reflects the infra-red (heat) component of the sunlight.  Here, lower numbers are what you want – less heat into the room.

Luminous Efficacy; the ratio of light to heat passing through a film.  Here, a higher number indicates more light, but less heat entering the room.

This basic knowledge is a starting point for your research and decisions based on your home and what is appropriate for you.  For instance, you may elect not to put films on North facing windows and doors.  Or you may opt to not install films on windows or doors that are shaded by awnings on your home or plantings in your yard.

From there, look for a window treatment that has the best combination of cost and energy saving for your home in your part of the world.  Work with the sales representatives of the various companies and dealers.  Make sure the various specifications are compared equally.  Ask them for samples.  Put these up on the windows you are planning to treat, and look through them; sunny day, cloudy day, night.  See which one offers you the view you want to see.  You can even try holding a heat source outside the window and holding your hand on the inside to see how effective the treatment really is.  Of course remember that long after you make the decision on which film or treatment to use, you will still have to live with it, so careful consideration is important – for your own happiness.

Make sure that, if you are replacing windows and then adding sun blocking film, that this does not void the warrantee on the windows.  If you are adding film to older windows, this should not be a problem.

Remember also, whether you are replacing windows or adding energy saving films, do not for get to ensure that all windows have good weatherization – no leaks where air can cost you energy and higher utility bills.

The important thing is to always think in energy saving terms so as you plan your home renovation, either with new energy efficient windows, or energy saving films or coatings, always look for ways to save energy and save money.


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