Tag: Alpen

High-Performance Windows & Air Infiltration

Generally speaking, windows are the weakest link in our building envelopes. When evaluating windows, often the insulative specifications (R-value / U-factor) are the primary focus. Just as important are the air infiltration rates. Code-built homes often lose 20 to 40% of the heat in the home through air infiltration. Windows and doors are a significant source of this heat loss. 

For windows and doors, air infiltration is defined as a volume of air (cubic feet per minute) divided by the window area (in square feet) when subjected to a 25mph wind (blowing perpendicular to the window) – Cubic feet per minute per square foot at 25mph windspeed.  As of 2017, window manufacturers were only required to report air infiltration numbers if the windows were to be labeled Energy Star. 

An Energy Star Compliant window allows air infiltration to be as high as 0.30 cfm/sq ft

Now some quick math for a 10sqft window:

0.30cfm/sqft x 10sqft = 3.0cfm total air infiltration allowed. 

To think about this another way: A basketball has a volume of 0.26 cubic feet. 

3.0cfm / .26 cubic feet = 11.5 basketballs per minute or 690 basketballs per hour from a single window. Imagine how much air this equals for a typical home of many windows. 

Now let’s compare an Advantage or Alpen High-Performance windows to an Energy Star compliant unit:

While we can’t prevent a basketball from being thrown through a window, let’s talk about how Advantage and Alpen prevent these air infiltration “basketballs”.

  1. Gaskets & Seals – While fixed units have the best infiltration rates, operable units must also be considered. Any sliding window uses a friction type gasket material to seal the window for air and weather. Over time this material can break down and will not perform as well as a compression seal. Consider awnings, casements, and tilt-turns which use compression seals rather than hung or sliders that use a friction type gasket. We always recommend against sliders and hungs and for fixed, casements, awnings, and tilt-turns. 
  2. Hardware – Consider the window hardware used to seal the windows. With a friction fit, there isn’t a practical way to better seal a window other than applying slight pressure or replacing the weatherstripping. With a compression style, minor hardware adjustments can be made to place more or less pressure on the seals, and while weatherstripping can be replaced, typically minor adjustments are all that is required to achieve an excellent air seal. 

High-Performance windows help create comfortable, quiet, high-performing homes conserving energy for future generations. We are burning through our fossil fuel resources rapidly and bad windows and doors are a primary source of wasted energy use.   If you have any questions about air infiltration or other aspects of high-performance windows, please call us at 720.287.4290 or send us an email. info@aebuildingsystems.com

High-Performance Windows

If eyes are the windows of the soul, then windows are the eyes of the energy-efficient home.

Generally, windows are the weak link in the walls of a home. “I love putting plastic on my windows to keep cold air out and warm air in,” said no one ever. That is why considering the brand and style of the windows in a home is just as important as deciding insulation and exterior materials.

The goal is comfort and operational cost saving, and the goal for builders and architects is providing both.

High performance windows are necessary in keeping with Passive Haus standards of efficiency: design, minimal thermal bridging, air tight, super insulated, optimized glazing, energy recovery ventilation and passive gains.

So we have learned that code built homes often lose 20 to 40% of the heat in the home through air infiltration, and windows and doors are a significant source of this heat loss.

To better grasp just how significant, imagine the volume of a basketball as our measure of air infiltration. According to the National Fenestration Ratings Council (NFRC), the maximum allowable air infiltration in a window, with the outside wind at 25 mph, is 0.3 CFM (cubic feet of air)/sq. ft. Air infiltration for a 10 sq. ft. standard window at the allowable maximum is 3.0 CFM or 11.4 basketballs per minute. At sixty minutes, one window allows in 684 basketballs per hour.

If you have (30) 10 sq. ft. windows, that equals 342 basketballs per minute or 20,520 basketballs per hour. That is a substantial amount of heat loss.

How do we reduce the basketballs?

Consider installing Alpen or Advantage Woodwork High-Performance windows. With a high-performance window, air infiltration at a 25 mph wind is <= 0.01 – 0.05 CFM (cubic feet of air). A 10 sq. ft. high performance window is at 0.10 CFM or .38 basketballs per minute or 22.8 basketballs per hour.

Therefore, (30) 10 sq. ft. windows equals 11.4 basketballs per minute or 684 basketballs per hour. We just went from 20,520 to 684 basketballs per hour. To summarize, that’s approximately a 97% reduction of air infiltration from what the NFRC says is acceptable.

The bad news is loss of air through a structure’s windows is like opening the windows and tossing our hard-earned money out of them. The good news is high performance windows fixes that problem.

The overall quality and performance of windows like Alpen or Advantage High-Performance windows is also superior. What makes these windows even more unique are their individual components, designed to combat heat losses (winter) and gains (summer):

  1. Frames – High performance windows have durable, low conductivity frames which generally include insulation. These frames offer better thermal performance. The R-value of most standard frames is r-2 to r-3.5. High performance window frames are r-4 and up to r-7, 8, and 9.
  2. Seals – High performance windows generally have multiple seals, which promote not only weather tight but also air tight seals.
  3. Glazing – IGUs (insulating glass units). Glazing can have double, triple and even quad glass. High performance IGUs have special coatings that high performance window manufacturers leverage to optimize heat gain from the sun in colder months and reduce heat gain and over-heating in the warmer months.
  4. Spacers – Depending on the material used, the spacers in between the IGUs can help increase the interior surface temperature of a window up to 15 degrees. For example, a galvanized steel spacer in a fixed high profile Alpen 525 window is rated R-5.9, whereas a stainless-steel spacer in a fixed high profile Alpen 625 window is R-6.7. Also, high performance window spacers reduce condensation on the edge of the glass (which reduces opportunity for mold and rot) and increases the inside glass surface temperatures, therefore improving comfort.
  5. Gas – There is “gas between the glass,” as it is denser than air and a reliable barrier to heat loss. Argon or Krypton gases are often used. Argon is much less costly, but Krypton increases performance and is often used in Passive House projects.

While ROI (return on investment) is important, comfort and unnecessary energy use are the primary reasons people pursue high performance windows.

High-Performance Windows help create high performance homes which conserve energy for future generations.  We are “burning” through our energy resources (coal and oil) rapidly.  Why not own a comfortable, energy efficient home that is also super quiet and will likely last much longer than your neighbor’s home?   And … let’s conserve our resources for future generations.

Please do not hesitate to call us at 720.287.4290 to learn more.