Mechanical heat-recovery ventilation is mandatory in Passive Houses because they're sealed so tight (0.6 air changes per hour) that fresh air must be supplied mechanically. The HRV draws in outdoor air while extracting stale air, and the outgoing air pre-heats the incoming air so winter ventilation doesn't introduce cold. You can still open windows, but the HRV lets the house stay sealed and maintain temperature control with far less supplemental heating than conventional homes.
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One of the other pillars of a Passive House is using mechanical heat recovery ventilation. The reason that you need mechanical heat recovery ventilation, or HRV as we call it, in a Passive House is because of one of the other pillars of Passive House, which is airtightness. So this house that we're standing in has achieved 0.6 air changes per hour. And so we have a heat recovery system installed. The heat recovery system essentially takes outside air, pumps it into the house, and at the same time passes it over the outgoing air that's being drawn out through the wet areas. So at the moment, we've got the heat recovery installed in the laundry, which is quite a common installation point. And so the laundry being a wet area, The window is one of the spots where air is drawn out of the house. That way, what happens is you're not, during winter, you're not pumping cold air into your house. The air is actually warmed up as it goes through the heat recovery unit by using the outgoing air. The big thing to remember with heat recovery units is that they are not air conditioners and they are not heaters. So their entire purpose is to keep the air inside the house fresh. A lot of people get There's a misconception about Passive House that you can't open the windows on a Passive House, and that's simply not true. However, when you have a Passive House, you are in control of the air temperature inside. So on a cold day like today, you can keep all the windows and doors closed, which will keep the heat that's generated in the house inside, and still have fresh air being constantly pumped into the home and exchanged with that warm air. That's inside so that you don't get your house cooling down. Whereas in another type of house which is not as airtight, you have the equivalent of having a window open all the time. So as you're heating the air in the house, that cold air is being drawn in under doors and around windows, and so you're constantly having to provide more heat to actually maintain a temperature. A Passive House with heat recovery ventilation, on the other hand, doesn't require as much additional energy to heat the air as you would with a normal home. If you want to know more about building a Passive House, download our guide to the 5 key skills of a Passive House builder.
