What happens if there is a power-cut?

Similar to normal houses, all mechanical systems will cease to work. However, because Passive House Buildings are so well insulated, they will maintain a higher level of comfort for much longer than would a normal house in the event of a power failure. If the power cut lasts for a prolonged period (say, more than 12 hours), then the windows can be opened to provide fresh air if required. Carbon monoxide alarms can be fitted in the house to detect reduced air quality.