Design Principles

The motto for building super high efficiency homes is “build tight, ventilate right”. When most people think of passive solar homes, they think of the homes built in the 70’s with huge south facing windows and concrete or stone inside the house for “thermal mass”. These homes were often epic failures in that they got way too hot in the summer and were very difficult to control. We’ve learned a lot since then.

RecoupAerator from Ultimate Air

An Energy Recovery Ventilator (ERV) like the RecoupAerator brings in fresh air from the outside while keeping up to 95% of the heat from the exhaust air.

Modern Passive Solar Design uses just the right amount of south facing windows. Instead of using thermal mass to store the sun’s heat, we simply don’t let the hot air escape by making the home extremely air tight. While it’s great to keep all of the hot air in the home in the winter, we still need fresh air to breathe. So we add a controlled mechanical ventilation system that ensures just the right amount of fresh air makes it into the house. This system, called an Energy Recovery Ventilator or ERV, moves fresh air into the home while exhausting stale air. A heat exchanger in the ERV uses the heat from the stale air being exhausted to warm the incoming fresh air, saving valuable heat in the winter. In the summer, we bypass the heat exchanger and bring in the cooler night time air to keep the home comfortable.


EcoAir Earth Tube System from Rehau

Earth Tubes pre-condition fresh air that is brought into the house by the ERV.

In addition to the ERV, Geos homes utilize “Earth Tube” technology from EcoAir. Earth Tubes are a simple concept where you lay a 8” diameter pipe around the entire foundation of the house at 5 to 7’ deep. Since the basement has already been excavated, it’s simple to install the pipe. One end of the pipe is brought to the surface. This is the intake. The other end of the pipe enters the house into the mechanical room. Instead of the ERV pulling fresh air into the home directly, the outside air is drawn through the Earth Tubes. Since the temperature of the earth at that depth is typically at a constant 55 degrees, the Earth Tubes can pre-condition the incoming air to the home. In the winter, the Earth Tubes warm up the cold outside air, and in the summer, they cool the hot outside air. When you combine the optimized shading from window overhangs and trees with the Earth Tubes, Geos homes maintain a comfortable temperature all summer long without the need for air conditioning.


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