Tag Archives: low-E windows

Low E Barndominium Windows

Being a life-long baseball fan, my first introduction to “Low e”, was former Mariner, Ranger, Angel, Indian, Blue Jay and Tiger relief pitcher Mark Lowe, who could chuck a rock as high as 101 miles per hour!

OK, not so funny, but it does illustrate how little I (and most people) knew or understand about low e windows.

For decades most post frame buildings were either cold storage, or rarely heated structures. With more and more post frame buildings being used as climate controlled homes, barndominiums and shouses (shop/houses) more efficient windows are needed, if not required.

What exactly is low e glass? Here are a few key technical terms about low e glass:

Low-emissivity: Low e glass coatings work by reflecting or absorbing infrared light and ultra-violet rays. A window with low e glass does a better job of keeping heat in during winter and out during summer.

Trickle VentU-factor measures how easily heat flows through a product. Lower numbers keep heat or cold exactly where you want it. Each state has its own set of U-factor ratings within its Building Codes.

Solar Heat Gain Coefficient (SHGC) tells how much heat radiation – due to sunlight – a window lets in. If heating your barndominium is your main concern, a higher SHGC can help offset some heating costs. In warmer climates, where air-conditioning costs are a bigger factor, look for a lower SHGC number.

Windows manufactured with low e window coatings typically cost about 10-15% more than regular windows, however these windows can dramatically reduce energy loss by as much as 30–50%.

A low e glass coating is a microscopically thin, virtually invisible metal or metallic oxide layer deposited directly on surfaces of one or more glass panes. This low e window coating reduces infrared radiation from a warm pane of glass to a cooler pane, thereby lowering U-factor. Simply put, a lower U-factor equals a more energy-efficient window.

Different types of low e glass coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain. A low e coating can also reduce a window’s visible transmittance (visibility through glass) unless you use a spectrally selective coating. Spectrally selective coatings are optically designed to reflect particular wavelengths but remain transparent to others. Such coatings are commonly used to reflect solar spectrum’s infrared (heat) portion while admitting a higher portion of visible light. They help create a window with a low U-factor and solar heat gain coefficient but with a highly visible transmittance.

Spectrally selective coatings can be applied on various types of tinted glass to produce “customized” glazing systems capable of either increasing or decreasing solar gains according to aesthetics and climatic effects desired.

All new windows have National Fenestration Rating Council technical labels applied, making it easier to understand above information.

If you live where heat/cold fluctuations are minimal, low e windows are probably not high on your list.  Living here in Northeast South Dakota where summers hover around 100 degrees and winters -20 to -40, you can bet low e windows are always on my shopping list when constructing a new post frame building.

Windows: Fill Them up with Gas!

Recently I wrote a blog post about Low-E windows. So Mrs. Guru, being an inquiring soul, read it, and wanted to know if our windows were gas filled.

Why would anyone want to fill the space between panes of window glass to begin with?

Well, as air transfers heat quickly, specific gases are used between window panes to improve energy efficiency. Both krypton and argon transfer heat less quickly than ordinary air, increasing the insulating value of the window. Krypton has better insulating properties than argon, but is more prone to leak.

Krypton is also much more expensive to produce than argon. Which makes krypton filled windows more expensive. When selecting windows, balance the expected savings of the higher insulating rating of krypton-filled windows versus the lower initial purchase cost of argon-filled windows.

Krypton performs best as an insulator when the spacing between the panes of glass is less than half an inch. Argon can be used in windows which have a wider space between window panes. For this reason, argon is often used for double pane windows while krypton is more often found in triple pane windows.

Compare cost against savings. Argon filled windows can save money over time with a lower energy bill, but if paying too much up front, the savings will never cover the investment. In addition, the argon does not help to deflect many of the sun’s ultraviolet rays, which aid in heating up your pole building. The additional heating will drive up summer cooling bills. If picking argon windows, get one with Low E coating to help reflect the sun’s rays.

A concern with argon-filled windows is an issue of leakage. Argon is a colorless and odorless gas, so it cannot be detected by humans, which means the argon could leak from the windows over time and never be noticed. One cause of leakage is an improper window seal. If the window seal has even a small gap in it, the argon will escape. Research on how the window is originally filled in the factory. A variety of methods, including a one-hole and two-hole method exist for placing argon in the window. Each method can affect how well the argon is trapped in the window. A one-hole method means only one hole was used to pump in the argon and gives the window less points to fail. The two-hole method means the seal had two holes to pump in the argon and there are twice the possible failure points.

Higher altitudes bring specific window concerns. Over 2,500 feet in altitude above where the window was manufactured? A capillary or breather tube should be added to prevent the change in altitude from causing a seal failure. Argon gas diffuses through the tubes very rapidly, and, by the time it reaches your home, there may not be any gas left. Window manufacturers are not liable because the window does not have to be tested for the argon content after it leaves the factory. Ensure, if building at a high altitude, the windows were manufactured at a similar altitude.

Spacing is another factor for argon retention. The spacer is the piece at the edge of the window which separates each pane of glass. Metal spacers are common and use a rubber compound to seal. Metal spacers are not as good as they will allow gas to leak out over time and they conduct both heat and sound. Consider non-metal synthetic spacers which seal better and will not allow the gas to escape.

With more pole buildings being used with climate controlled interiors, windows become more significant. Making careful choices and doing some research can either pay off with big savings, or involve costs which can never be recouped.