You don’t have to go back to the Stone Age to have a more efficient home, but it certainly can help a “ton!” Our friend, John Avenson, has employed a few simple techniques to manage stratification inside his home, and he’s turned to a few rock-solid solutions to do so!
We’ve talked about convection currents inside a home, and how warm air naturally rises and pools near the ceiling and upper floors. That effect, known as stratification, can leave the top of a house too warm while the ground floor stays chilly. It is a common headache in multi-story homes, especially ones with tall, open stairwells or great rooms. But stratification is not a problem to solve so much as an opportunity to manage, and one Colorado homeowner figured that out more than forty years ago.
Meet John Avenson
John Avenson is a friend of AE Building Systems and a passionate advocate for energy-efficient living. His Westminster, Colorado home was built in 1981 with help from the Solar Energy Research Institute (SERI), the predecessor to the National Renewable Energy Laboratory and more recently National Lab of the Rockies. As part of the Passive Solar Design approach in the U.S., John’s home applied many of those principles: south-facing glazing, generous thermal mass, and a floor plan designed to work with the sun rather than against it.
*We will state a quick caveat that we are not in the business of selling rock boxes or passive solar retrofits, but John’s approach is a great real-world illustration of how stratification can be turned into free heat instead of wasted energy. And, we’re big fans!
The Rock Box: Turning Rising Heat Into Stored Heat
During the day, sunlight pours through John’s large south-facing windows and heats the air inside the house. Left alone, that warm air would simply rise and stratify near the ceiling. Instead, John’s home actively pulls that hot air down and pushes it through a rock box: a five foot by five foot chamber, ten feet tall, packed with rounded river rock. The round rocks allow air to flow freely between them, and as the warm air passes through, the rocks absorb and store the heat.
When the sun goes down and temperatures drop, the process reverses. The rocks slowly radiate their stored warmth back into the home overnight, smoothing out the temperature swings between day and night. It is a simple, mechanical solution to a physics problem, and it means John’s furnace barely has to run through a Colorado winter.
Why Thermal Mass and Solar Gains Matter
The rock box works because it pairs two passive solar fundamentals: solar gains and thermal mass. Solar gains are the free heat energy that enters through south-facing glass. Thermal mass, whether it is river rock, interior brick, or an insulated concrete foundation, is what stores that energy so it can be released later instead of escaping through the roof. John’s home leans on both, along with insulated foundation walls and a tightly sealed envelope, to keep those gains where they belong.
A Window into the Solution
Avenson’s home is also equipped with high-performance Alpen windows, which are products we provide our clients. Alpen windows achieve high energy efficiency through their patented AlpenGlass technology, which utilizes suspended films and ultra-thin glass in triple- or quad-pane configurations. These panes, paired with super-insulated, thermally broken fiberglass frames, create an exceptional thermal barrier that minimizes heat transfer and condensation.
Alpen photos
A Comprehensive Approach
John Avenson’s home is one that employs a few key strategies, but if you dig in deeper (watch the video below!), you’ll quickly see that this home has thought through so many angles to be energy efficient and harness passive management strategies.
A Lesson for Any Home
Most of us are not building a rock box into our next remodel, nor can we retrofit our entire house in one season, but the underlying lesson applies everywhere: air sealing, thoughtful glazing, insulation and thermal mass all work together to manage the convection and stratification already happening inside your home. Choosing high-performance windows that control solar heat gain and limit unwanted air leakage, like those from Alpen Windows, is one of the most practical ways homeowners today can apply the same thinking John put to work in 1981.
Curious how your home’s envelope and windows measure up? Visit AE Building Systems to learn how high-performance products can help your home manage heat too!
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