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Wasn't sure where to post this but here's our observations after storm Eunice passed through. Initially we watched the storm gather, we could see that that the wind was strong but from inside there was no indication, no sound, no draughts. As the wind picked up something we were not expecting happened, we could hear and feel a draught. We have two fairly large sliders and at the peak of the storm, the wind was pushing against the slider so much that there was airflow between the slider and the fixed pane. Not much and not continuous but it was definitely happening. Our air test was done to passive standards (positive and negative pressure) so we're fairly certain there is no problem with the sliders because if there was then the negative pressure test would have exposed that. Anyone have a contradictory view? A short time later we had a power cut , that doesn't matter. The house is warm, the Sunamp is fully charged (minus two showers), what could go wrong? Well, we're fully electric so there was no cup of tea to sup whilst watching the storm play out. Information gleaned is that the power will be out for over 48hrs And of course there's no heating. But what does that matter because the house is toasty warm at about 21.5° and we've not had any heating on for days. And the house is almost airtight, apart from the few blasts that squeezed through the sliders. Thanks to @Adrian Walker's advice we have a CO2 monitor, well we bought a couple. It was quite amazing how quickly the CO2 PPM started to increase after the power cut. Obviously the MVHR was having a bit of "quiet time", so now we had a toasty warm passive house that was not working as planned. As night drew in it got worse because lots of candles were lit. The only solution was to open some windows and get some airflow. Out of interest, it was only the monitors that informed us of the poor air quality, it wasn't something we sensed. So, we have a toasty warm passive house but with no airflow so a couple of the 'tilt and turn' windows on opposite sides of the house were tilted. That fixed things, air quality wise, very quickly but it also meant the passive house was now going to cool down more rapidly than planned. There are no heating options, apart from the bio-ethanol fire) so we were getting ready to break out the cold weather gear. Fortunately power was restored about 12 hours after the cut. We have a fair amount of PV, and it was quite a sunny storm but of course the PV trips off in a power cut. We were meant to have a battery system but the that didn't happen. The M&E individual who specced that (and didn't provide) had wired in an emergency power supply from which we could run the fridge and freezer in the event of a power outage, which was a pretty smart idea, shame it never happened, but actually my advise to anyone building to passive standards, if they have a battery system then make sure that the MVHR will run off the batteries. That's the main thing we've learned. If you have built to passive standard and have a battery system, make sure your MVHR can run from the batteries in the event of a power cut, I suspect most battery systems will power an MVHR unit for ages. Without that, you're not in a passive house anymore. Oh, and we had the first BBQ of the season this evening. Bit nippy!