Looking Through Windows — Part 1
Selecting the right windows means juggling performance specifications, warranties, availability, and price
[Editor's note: Roger and Lynn Normand are building a Passivhaus in Maine. This is the fifth article in a series that will follow their project from planning through construction.]
When we first began looking at windows for our Passivhaus project, we started with a list of 15 window manufacturers. We whittled the list down to two: Schüco, which on paper looked like the best European-style window, and Pella, the best North American style window.
Our architect, Chris Briley, has further refined the south facade of our house to add more glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. and reduce the roof overhang. Both actions were meant to enhance the net solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. of the house and hopefully get us into compliance with the Passivhaus standard.
Image 2 (below) shows what the revised south facade now looks like. The windows are now wider and taller, and the number of venting units is reduced.
After visiting both Schüco and Pella showrooms and doing further research, we have decided ... to look at other options.
The Schüco windows have great performance specs
Marc Rosenbaum, our Passivhaus energy consultant, ran the PHPP software and concluded that we met the Passivhaus standard with the Schüco windows without further modifications to the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.. His analysis showed that the Schüco windows yielded a total annual heat load of 4,350 BTUBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /square foot, comfortably below the Passivhaus standard of 4,760 BTU/square foot. (A lower annual heat load is better.)
But after looking closely at the Schüco windows and reflecting on them, we have decided not to use them. There was no single objection, but rather an accumulation of concerns, mostly subjective, that left us feeling uncomfortable. For example, a week after our meeting, we still have not received additional promised information, including a copy of the warranty.
The Schüco website only lists commercial windows and makes no mention of residential windows, nor does it provide any links to U.S. distributors. We were told that Schüco divested its residential window business some five years ago, so it was unclear who (Schüco or the Massachusetts distributor) would honor any product delivery concerns or future warranty issues.
There was not a solid heft when we tried opening and closing the heavy triple-pane windows. Perhaps that is due to Schüco using a thin aluminum reinforcement within the sash and frame rather than heavier gauge shaped steel we have seen in a competitive PVC window manufacturer.
Pella windows are nicer, but they don't perform very well
We found the Pella windows to be superior to Schüco in all aspects except for performance. Since the Pella specs were not as good as those from Schüco, we knew it would cost us more money to upgrade other portions of the building envelope if we were to select Pella.
We were surprised and dismayed to learn the results from Marc – using the Pella windows in our design yielded a total annual heat load of 7,960 BTU/square foot – well above the Passivhaus standard. The difference is mostly due to Pella’s poorer glazing. The overall R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of the Pella window is R-4 – only half that of the Schüco.
Regrettably, Pella’s top triple-pane kryptonA colorless, odorless inert gas, often used with argon in fluorescent lighting and sometimes used as gas fill in high-performance glazing.-filled window is inadequate for use in our Passivhaus! The incremental cost of enhancing the building envelope to make up for the low performance of the Pella window approaches that of the cost of the windows themselves.
So we will look at two other alternatives. Stay tuned!
- Schüco International KG
- Chris Briley
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