The 2019 polar vortex produced -24 F lows that averaged approximately -17 F for 34 consecutive hours. Ellis Passivhaus maintained an interior temperature of > 71 F throughout, far above the required 68 F design temperature. The Zehnder ERV (energy recovery ventilator) continuously delivered fresh filtered air while retaining > 84% of the energy in the extract air stream. Despite 54,000 BTU of heating capacity (and 48,000 BTUs of cooling capacity) actual use averaged 7.5 kWh per hour (< 26K BTUs) during the 48 hour event. 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 while showcasing the resiliency of Ellis Passivhaus itself. Contrary to expectation the actual energy expense incurred was nearly at parity with the natural gas price despite a doubling in actual spot electrical price apparently induced by the event. Given ComEd’s hourly pricing program, credit is due to Mitsubishi’s Hyperheat air to air heat pump platform that is normally 2 - 4 x more efficient than new boilers or forced air systems. 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 meticulous attention to detail the construction crew exercised in implementing air-tightness and insulation details.