In a series of back-of-the-napkin sketches of his energy-efficient dream home for the off-grid wilds of central Alaska, Karl Kassel came up with an octagon shape. It was a compromise between a circle (the shape with the highest ration of area to perimeter) and a square (the handiest shape for builders to work with).
Aside from that ratio, the advantage of a circle or an octagon would be that a single fireplace in the center could touch—and heat—all of the rooms. We aren’t talking about any ordinary fireplace, now. This is a masonry heater or kachelofen, an enormous mass of masonry built around the intricate flue of a rather small firebox.
The strategy of operation … is to burn fuel quickly at very high temperatures. Flue gases pass through a series of serpentine channels inside the stove before exiting, transferring heat to the large mass of the stove (typically around 10-12,000 pounds of concrete and stone) and lowering the exhaust temperature to around 110°F. … High temperature allows full combustion and results in the very clean burn characteristic of masonry heaters. (Rich Seifert in Alaska Building Science News.)
In the bathroom, a soaking tub nests into the masonry of the back of the fireplace, and circulates its water through pipes buried in the masonry, maintaining perfect 100° water at no added energy cost.
The stove “can produce fine breads, pizzas and more in the winter, but is quite useless in the summer, unless you’re interested in a sauna at the same time.” (I wonder if pizzas have to be fired in the mornings, at most times of year.) Similarly, it heats the home’s hot water in winter, but turns that task over to solar water heaters in summer.
Sunset Roost sits outside of Fairbanks on a hilltop with a view of Denali in the West. The hill has several houses but no power grid. The average January afternoon high here is 0°F. (This is much colder than Dillingham, which in turn is much colder than most parts of Norway and Sweden, where quite a few Passive Houses have been built.)
Sunset Roost is a truly imaginative suite of technologies well suited to its site. It has R65 walls, R85 roof, triple glazing, 3 kW of wind generation, 1.6 kW of solar (useless here in midwinter), and a buried 12,000 gallon water tank that stores energy in the form of heat at times when an surplus is produced. There is a diesel generator and a propane water heater for backup, but they aren’t used much. Two cords of firewood get it through the winter, including heating domestic hot water.
The builder, Thorsten Chlupp, must have liked Sunset Roost a lot, as he followed it up with a house for himself that also centers around a masonry and also borrows heavily from the Passive House (PH) playbook. Both houses have water pipes for radiant heat built in their concrete floors, but haven’t used them yet; apparently the wood stoves suffice. Firewood is an abundant resource here, and people enjoy putting it up for the winter. And remember: two cords. Not a lot of wood for a house in the Arctic.
Both houses—as well as the World’s Tightest House in Dillingham—owe a lot to technologies developed by the Passivhaus Institut, but all three fall short of PH standards in one way or another. This suggests that PH standards have a ways to go to truly embrace climates and environments very different from Germany’s.