carri's passive house adventure: searching for the perfect passive house window

February 16, 2014

While we continue to wait for our long lost grading permit, we've been exploring window options for our Net Zero, Passive House.  We decided to look at three options:

1) We were willing to take a hit on window performance and use a wood stove more, maybe even forego Passive House certification, if we could save a substantial amount on standard, double pane, low-e North American windows.  We replaced our 1920 bungalow double hungs with Loewen many years ago and have always been impressed with their quality, aesthetics and performance.  Therefore, we chose Loewen windows for the standard, double-pane window variable.

2) As we are always prioritizing US made and/or locally made over shipping from far away and mass production for our house, we wanted to give the newly Passive House Institute US certified Marvin window a chance.  Variable number two.

3) A European window.  Currently, there are many beautiful, high performance European windows readily available to the US market.  I've always had an architectural affinity for Zola windows and based on past experience, they've been cost competitive with the other European manufacturers. Variable number three.

We sent the same window package to all three companies, asked for the same sizes and hardware.  Our goal was to have the best apples to apples comparison of the three variables.


1) We went through the Loewen rep we've known for years and he had the window package priced using the best performing glass combination available in double pane glass. (U-value .26, SHGC .28) This was a simple and quick turn around.  Actually, we initially had Loewen price triple pane windows thinking that maybe that could potentially save money with just a very small reduction in performance (U-value .20, SHGC .36).  See chart below for numerical results.

2) With Marvin, we had a very informative conference call with the research team and Marvin tech rep from the main factory.  They walked us through what allowed their window to meet Passive House requirements. Essentially, they are meeting the standard through a series of films, coatings and high performance glass.  European windows have a modified frame and a much thicker sash.  And also unlike European windows, Marvin's PH certified window is only a fixed or casement configuration.  Casement did not really work with our design, and frankly I'm not a fan of the interior aesthetics of the Marvin casement window, but again we were willing to compromise for a US made window.  The turn around time for a quote was significant and it was very overwhelming for us to figure out which option of films to select for which performance, they were almost too unlimited. I think we ended up with a U-value of .12 COG and a SHGC of .50

3) Dealing with Zola was by far the easiest and most comfortable.  There's something to be said about working with people who speak the same language, can offer value engineering and technical support. Zola's windows are Uvalue of .09 COG and SHGC of .54

"I can't afford a Passive House because those fancy European windows are just so darn expensive. End of conversation."

We would like to announce to the Passive House community and anyone seeking Passive House design that this myth is bunk. We would really like to have supported a North American manufacturer, but the numbers just don't make sense.  Not even close sense. The Loewen double pane window is a 20% savings, $9,600, but it performs less than half as well, so it doesn't seem worth the savings. Also, the knowledge of Passive House detailing within the Zola company is worth a lot of that difference.
window cost comparison.jpg

*I do want to add, we are comparing to quality wood clad windows, not vinyl windows available at Home Depot.
*The cost of shipping of the Zola windows is roughly cancelled out by the sales tax on the other two.