Homelink's engineers wanted to prevent the typical pressure variations between rooms that are found in modern, tightly constructed homes. Part of their solution called for strict control of airflow by way of an airtight envelope--including windows. The other half of the equation meant allowing conditioned air to flow passively through "jump ducts" in walls.

"We effectively keep all of the air movement within the building shell," Lstiburek explains. "There's no ductwork in attics or exterior walls. That's key." As a continuation of the wall spaces, the use of wood trusses for floors created ample, forgiving space for running insulated ductwork, along with copper plumbing and structured wiring.

In the lower level mechanical room, insulated ducts feed the high-efficiency Carrier HVAC equipment, which includes dual speed air conditioning, gas furnace, electronic air cleaner, whole house humidifier, zoning system, and energy recovery ventilator.

And, of course, the walls also conceal the builder's many efforts to apply BSC's optimal framing system, including special "open" headers above doors and windows, single top plates, and open corners. As a result, more square feet of unfaced Owens Corning fiberglass batts could be squeezed into wall cavities--improving the home's R-values.

In addition, HVAC equipment was sized somewhat smaller than would be expected in a home this size. Lstiburek felt the tonnage could have been even less, but HVAC installers decided to err on the side of caution. The result, a two-speed Carrier condensing unit, capable of adjusting to any load between 2 1/2 and 4 tons.

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