Although not an official standard, a ZEH home (or ZEB) must obtain a HERS index of 0. This level indicates that the home has increased insulation levels and uses only site generated energy such as photovoltaics or wind generation.
Collette & Ed, Derry, NH “We love this house! Thermally, it works very, very well. It gets easier to heat every year and is always quite cool in the summer.”