UPDATED on August 22, 2017 with a new author’s postscript.
Longtime readers of GBA know that I get frustrated by exaggerated energy savings claims. A glaring example is the statement that “a Passive House building uses 90% less energy than a conventional building.” A variation on this claim: “A Passive House building uses 90% less energy than a code-minimum building.”
It doesn’t, of course. The oft-repeated falsehood is based on a boast made by Wolfgang Feist in the 1990s. Back then, Feist claimed that a new Passivhaus residence needed 90% less energy for space heating than a “conventional” residence in Germany. (It’s important to remember that space heating energy is just one small part of the energy-use pie.) The “conventional” residence that Feist was talking about was an average German home, not a new house meeting modern code standards. (Many German homes are decades, or even centuries, old.)
These days, Dr. Feist and the Passivhaus Institut are usually more careful in their statements than many of their enthusiastic followers. That said, it’s easy to find a Passivhaus Institut document online that includes the boast, without any qualifications about space heating or the age of the housing stock that is used for comparison. Here are two sentences from a Passivhaus Institut press release published in December 2015: “Feist built the world’s first Passive House almost 25 years ago. Still today, this terraced house in Darmstadt (Germany) consumes about 90 percent less energy than conventional buildings.”
As I said, it doesn’t. Let’s peel the onion and figure out why.
What two homes should we compare?
Let’s say that a young couple has money in the bank and wants to build a new energy-efficient home. The couple is weighing…