High-performance windows provide views, connections to the outdoors, and even a means of emergency escape. In addition, they can make a home more energy efficiency by capturing passive solar heat gain and daylight. How much depends on the design of the building and the orientation of the windows. And on the windows. Even with long, cold winters, a high-performance window can bring in more heat by solar gain than it loses. However, conventional "code minimum" windows will typically lose far more heat than they will harvest. So, for a Passive House, careful window selection is essential.
And there is another reason windows bear extra scrutiny: most windows do not insulate nearly as well as the exterior wall of even a conventional, non-Passive House building. However, windows vary greatly in their thermal performance. The highest-performance windows available in North America may insulate up to 4 times better than the worst-performing window allowed by building codes.
And this is not important only in winter. Insulation is also important in summer. Just as poor performance windows transfer far more heat out in winter than a Passive House window, the same poor performer allows more heat to invade your home on a hot summer day than a super-insulating window. Thus, these windows can reduce your air conditioning.
A simple, but often overlooked important quality of a high performance window is to be airtight when closed. Just as with the rest of the building enclosure, windows must not leak warm air out of the home in winter or hot outdoor air into the home in summer. Thus, all "operable" (opening) high-performance windows should have multiple, durable, continuous seals and multi-point locking mechanisms to ensure they do not leak air when closed.
At the same time, windows can transmit a large quantity of heat through conduction. You feel this conduction if you put your hand on the inside of a window on a cold winter day and it feels cold to the touch. It shouldn’t.
The inside surface of a high-performance window feels about the same temperature as the inner surface of your exterior walls on a cold day. Try this test on your windows!
Tanner. Wood frame windows engineered and built in Europe. Aluminum cladding option. Complete line incls. historic appearance Brooklyn Double Hung Windows, swissFineLine hidden frame windows. Triple glazing, warm edge spacers, low-e coatings, gas fills, triple seals, multi-point locks, multiple drainage layers.
THANK YOU FOR YOUR CONTRIBUTION
Henselstone (Thanks to Vincent Fournier)
Eco Windows (Thanks to John Rountree at Rountree Architects.)