The 2019 polar vortex produced -24 F lows that averaged approximately -17 F for 34 consecutive hours. As many witnessed, Ellis Passivhaus maintained an interior temperature of > 71 F throughout, far above the 68 F comfort standard. The ERV (energy recovery ventilator) continuously delivered fresh filtered air while retaining some 84% of the energy in the extract air stream. Despite the heating system’s rated capacity of 140 kW per hour (48K BTUs), use approximated 7,5 kWh per hour during the 48 hour event or ~ 90% less than comparable Chicago stock. All systems performed flawlessly. Extreme temperatures far below the -3.2 F (99.7%) design temperature induced a minimal increase in kWh demand proving the inherent robustness of the Passivhaus Institut Building Standard and the resiliency of Ellis Passivhaus itself as it passed through uncharted territory. Contrary to expectation the actual energy expense incurred was nearly at parity with natural gas despite a doubling in price apparently induced by the event. Given ComEd’s hourly pricing plan, credit is due to the air to air heat pump technology employed that is normally 2 - 4 x more efficient than boilers or forced air systems typically employed in most homes. This combination is all the more compelling because Chicago normally pays ~ 14% more per kWh and ~ 31% less per Therm when compared to a cross section of major US cities. That said, the low energy demand Ellis Passivhaus required in the first instance rests entirely with the Passivhaus Institut Building Standard and the construction crew who implemented the plan.