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Historic Solar House Has Been Bulldozed

George Löf’s pioneering solar house — a 1956 house in Colorado with an active solar air system — has been demolished

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In the mid 1950s, solar pioneer George Löf built this modern ranch house in Denver. The house had an active solar heating system that included solar hot air panels mounted on the roof.
Image Credit: Historic Denver
In the mid 1950s, solar pioneer George Löf built this modern ranch house in Denver. The house had an active solar heating system that included solar hot air panels mounted on the roof.
Image Credit: Historic Denver
In 2011, two years after Löf's death, the house was on the market awaiting a buyer.
Image Credit: Anthony Denzer
These sturdy red cardboard tubes were filled with gravel. Hot air from the solar collectors could be directed to the gravel bins, which acted as thermal storage batteries. This illustration of George Löf’s heating system appeared in the February 1958 issue of Popular Science magazine.
Image Credit: Popular Science

Here is some sad but not surprising news: the George Löf house — one of the seminal buildings in the history of the solar house and certainly a modernist landmark worthy of protection and preservation — was recently destroyed. I visited the Denver site earlier this year and found a large excavation and a foundation (presumably) for a McMansion.

Most of us associate the term “solar house” with the 1973 energy crisis. But the feasibility of solar houses in the 1970s would have been impossible without the earlier exploratory work by pioneers such as George Löf. The house Löf built for himself in Denver, in 1955-56, was a seminal experiment in solar heating, using an innovative system of rooftop collectors, solar-heated air, and gravel storage. It “became a model for emerging solar home heating systems and attracted engineers from around the world,” according to the Wall Street Journal.

Present at the creation

Nobody played a more enduring role in the 20th-century solar house movement than George Löf. He was present at the creation, so to speak, having been a student of Hoyt Hottel when Hottel built the first-ever “active” solar thermal house at MIT in 1939. In 1945, Löf built the first active solar air system, a precursor to the system installed in the Denver house. He would remain active in the field for decades, and served a term as president of the International Solar Energy Society.

In the 1970s, the George Löf house was frequently hailed for having the oldest continuously operating active solar heating system in the world. Löf lived in the home until his death in October 2009 at the age of 95. (For more information on George Löf, see my book, The Solar House: Pioneering Sustainable Design, or George Löf: Denver’s Solar Pioneer. A February 1958 magazine article on the George Löf house is available online: “Will Your Next House Get Its Heat from the Sun?”)

A tear-down

Prior to the demolition, the Löf house was in original condition, including the flat-plate solar collectors (air heaters) on the roof. It had hardly been touched since its construction 57 years ago: not even a coat of paint in my estimation. Image #2 (below) shows how the Löf house looked when I visited it in September 2011.

At that time (two years after Löf’s death), the house was vacant and for sale. Because of the large size of the lot, the condition of the house, and the (wealthy) neighborhood, it was predictable that the house would be purchased as a tear-down. At that time I contacted the realtor and local preservation groups to make sure that the house’s importance was understood, but obviously to no avail.

As I document and discuss in great detail in my book, the Löf house was remarkable for its technical innovation and for the sympathetic relationship between the architects (James Hunter of Boulder, assisted by Tician Papachristou) and the engineer (Löf). The design was celebrated by the New York Times for its heating system and Hunter’s “modern lines.”

The rooftop collectors, still in place in 2011 and just barely visible behind plywood screens, produced hot air which could be sent straight to the rooms of the house or to gravel tubes that were used to store the heat. The sympathy between architecture and engineering was expressed most beautifully by Hunter’s decision to place the cardboard tubes near the staircase in the center of the house, visible from the entrance, and to paint them bright red. (And in a wonderfully poetic contrast he formed a concrete chimney from the same type of cardboard tube, and painted the chimney a cool blue.)

Only photos and the blueprints remain

I visited Dr. Löf at the house just a few months before his death. He was bright, and we had a long conversation.

He gave me the original set of blueprints to the house, and I suspect, sadly, that he recognized that the drawings wouldn’t be needed by the next owners of the property.

Anthony Denzer teaches architectural engineering at the University of Wyoming and is the author of The Solar House: Pioneering Sustainable Design.


  1. dankolbert | | #1

    Sad story, great piece
    Thanks for the history lesson. What a shame.

  2. GBA Editor
    Martin Holladay | | #2

    Solar pioneers
    These days, now that we understand the importance of airtight construction methods and the advantages of superinsulation, it's easy to dismiss those who use active solar thermal equipment as misguided. But the pioneers of the 1940s and 1950s were visionaries, and all of us in the green building movement stand on their shoulders. When I began working as a builder in 1974, the "solar house" movement was still with us, and we all eagerly read the stories of pioneering work by the 1939 MIT team and George Löf. (I first learned about the 1939 MIT researchers in a college engineering course I took in 1973).

    Indeed, the story about the destruction of George Löf's house is sad.

  3. Ericwest1 | | #3

    Denver looses another great house
    This was in interesting house from both a solar heating and mid-century modern design. Too bad it's gone.

    More pictures in this slide show from Historic Denver

  4. kevin_in_denver | | #4

    George Lof
    Anthony, thanks for caring and following this story.

    I studied under George at the CSU SEAL in 1978-79, and was the design engineer for Solaron (the company he founded) in 1982-83. My father attended East High in Denver with him in 1930-1931.

    At Solaron, my main job was to expand our market share in water-based solar thermal because we had been learning that air-based systems were relatively inefficient. That was a bit ironic because Solaron was the world leader in air-based solar and George had been the world's leading expert in the field for over 40 years by that time.

    Now, liquid based solar thermal is being supplanted by net-metered solar PV for economic reasons. And my company is tearing down old homes in Denver near light rail and replacing them with PV powered net zero homes. Passive solar is still in the mix when possible, but Denver's street grid only allows 10% passive solar homes.

  5. Floozina | | #5

    I really thought that this type of wanton vandalism was a feature of this country (Australia) but it seems I was mistaken. From the photographs it appears that this important house was not beyond rescue, but the line in the report about the footings for a McMansion being in place is extremely alarming. When are governments - because consumers, builders and many designers are not - going to recognise that the planet can not support the endless proliferation of McMansions? If it requires legislation, then so be it, although given the current hooha in your country about the introduction of Obama's health care policy, I guess I am off with the fairies. I am still fuming however.

  6. Tony Denzer | | #6

    Thank you for the comments,
    Thank you for the comments, everyone. If you're interested in the general subject of early experimental solar houses, please visit

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