Building Ω-Mechanical Systems

A Wisconsin couple, Clay Yapp and Danielle, built a 1,536-square-foot net-zero home largely on their own in Wauzeka (a cold climate zone), and the mechanical systems they chose show what it takes to heat and cool a very airtight, well-insulated house efficiently. Rather than buying a standard furnace or central air system, Clay ran a room-by-room heat-loss calculation (called a Manual J) to find out exactly how much heating and cooling the house actually needed. Because tight, well-insulated homes need far less capacity than typical houses, he sized the equipment small on purpose: a 9,000-Btu ductless heat pump (a compact unit that both heats and cools by moving heat rather than generating it) for the main floor, and a 6,000-Btu unit upstairs. Slightly undersizing the units, he explained, avoids the on-off cycling that wastes energy and actually improves the system's ability to pull humidity out of summer air.

For fresh air, the house uses a fully ducted energy recovery ventilator (a system that swaps stale indoor air for outdoor air while recovering some of the heat or coolness from the air being exhausted), pulling humid air from the kitchen and bathrooms through a filter before it leaves the house. The broader lesson for any homeowner is that once a house is sealed and insulated well, mechanical equipment can often be smaller, cheaper, and more efficient than what a standard installer might otherwise size for a home of the same footprint.