Best of all, the entire system is weather-responsive, equipped with sensors that monitor everything—from outdoor temps to the number of zones in the house calling for heat to the airflow demand on the ducts—and adjust both the water temperature and the fan speed accordingly. "On a cool fall day, the system will produce a slightly warm, gentle flow of air," says Richard. But on a frigid day in January, the air in the ducts could be 20 degrees warmer and moving much faster. Combine that with the house's super-insulated envelope—and the mini-duct system, which is designed to mix the house's indoor air to avoid hot and cold spots—and John and Sally will get both efficiency and superior comfort. Richard estimates that the system he designed will operate about 20 to 25 percent more efficiently than a conventional heating system.
Shown: The condensing boiler also feeds the supplemental radiant floor heat on the first floor and in the bathrooms, which is designed to take the chill out of the air on days when using the full heating system would be overkill.