Replacement Windows-Air Infiltration
By Betty Stephens
Air infiltration refers to air leakage through unsealed joints in a structure and around the windows. The Air Leakage (AL) rating pertains to leakage through the window assembly itself. Air infiltration can also occur around the frame of the window due to poor installation or poor maintenance of existing window systems. Make sure windows are properly installed and maintained (caulking and weather-stripping). Cold glass can create uncomfortable drafts as air next to the window is cooled and drops to the floor. This is not a result of air leaking through or around the window assembly but from a convective loop created when next to a window is cooled and drops to the floor. This air movement can be avoided by installing high-performance windows.
Heat loss and gain occur by infiltration through cracks in the window assembly. It is indicated by an air leakage rating (AL) expressed as the equivalent cubic feet of air passing through a square foot of window area. The lower the AL, the less air will pass through cracks in the window assembly. At this time, the AL is optional among NFRC ratings. For code compliance purposes, however, air infiltration is often tested in accordance with the North American Fenestration Standard (NAFS), which produces similar results to the NFRC air leakage rating. Select windows with an AL of 0.30 or less (units are cfm/sq ft)
The American Architectural Manufacturers Association (AAMA) reports that any residential window that achieves a rating below 0.30 cfm/Sq.Ft meets the requirements for their gold rating. This is the best rating they offer. This is also the minimum air infiltration rating for the energy star program. This minimum rating may be reduced with the 2015 energy star program.
How do you know if there is Leakage?
The two recommended options in determining if a window, door or skylight will allow in too much air:
• Look for an AAMA certification label on the window to determine that the product has been designed to meet air infiltration standards.
• Determine if the product has been tested and authorized for AAMA certification by researching the product in the AAMA Certified Products Directory. Contact the manufacturer of your specific product to request test data.
Note: Certification programs offer enhanced quality that is not built into the basic testing process. Certification quality control measures include two unannounced manufacturer plant inspections by a third-party validator.
There are many factors to consider when choosing a replacement window, including visual appeal, style of operation, affordability, and last but not least is performance.
1. Structural Integrity
Structural integrity is the ability of a structure or a component to withstand a designed service load, resisting structural failure due to fracture, deformation, or fatigue... Structural integrity is the quality of an item to hold together under a load, including its own weight, resisting breakage or bending. It assures that the construction will perform its designed function, during reasonable use, for as long as the designed life of the structure. Items are constructed with structural integrity to ensure that catastrophic failure does not occur, which can result in injuries, severe damage, death, or monetary losses.
2. Thermal Performance
Thermal performance of a building refers primarily to how well a building is insulated from the external weather conditions in order to achieve a comfortable temperature internally. This means keeping the internal temperature higher than the external temperature or lower than the external temperature (not a common occurrence in Ireland). The comfortable range of room temperature is 19-22 degrees C.
There are a number of factors that determine the thermal performance of a building. The best known factor is the insulation value of the materials used in the fabric of the building (i.e. floors, walls, roof). This value is known to most of us as the U-Value of the material. The lower the U-Value the better. If the U-Value of a material reached 0 it would prevent any energy (heat) from being lost.
Other factors that influence the thermal performance of a building are air-tightness, cold-bridging, junction details and how the materials are brought together or fitted on site. If a high performing material is poorly fitted its effectiveness can be dramatically reduced. One result of poorly installed insulation is “thermal looping”. A thermal loop is a movement of air driven by warm air rising at one end of the loop, and cool air descending at the other end, creating a constantly moving loop of air.
U- Values are a true reflection of the thermal performance, only when the insulation is fitted correctly. No matter how thick the insulation is or how good the material is, if it isn’t fitted correctly and an air gap is formed then the performance of the structure is drastically affected. Heat flows from a high temperature point to a cold temperature point, and will find the path of least resistance. In a traditional masonry structure where an air gap occurs between the insulation and the cold masonry/block surface, air can circulate from the warm side of the insulation to the cold side. The heat is pouring out at this point.
The Best Windows from Consumer Reports' Tests
New windows can make your home quieter, more attractive, and less drafty, and they don't need painting. But replacing your windows is expensive, and there are lots of decisions to make before you swipe your credit card. Here’s what you need to know plus some window picks from the experts at Consumer Report:
The best windows from tests
In our tests of wooden, vinyl and fiberglass double-hung and casement windows we found 12 that performed well enough to recommend including four that we named CR Best Buys. Here is the top model of each type we tested.
• Wood double-hung: Andersen 400 Series, $310 per window
• Vinyl double-hung: Simonton Pro-Finish Contractor, $260
• Fiberglass double-hung: Integrity from Marvin Ultrex, $450
• Wood casement: Andersen 400 Series, $400
• Vinyl casement: American Craftsman by Andersen 70 Series, $260, sold at Home Depot
For more choices see our full window Ratings and recommendations and read our recent reports, "How to choose replacement windows" and "When to repair and when to replace your windows.