Heat Recovery Ventilation Rundown

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There’s a lot to cover about MHRV, but this article covers the basics:

MHRV, or Mechanical Heat Recovery Ventilation is a vital aspect of the Passivhaus design system – but it can also be used as part of any other high-performing, airtight build. In fact, once a build passes a certain threshold of airtightness it becomes essentially a necessity.

Put simply, it’s a continuous, highly efficient ventilation system designed to mechanically regulate air temperature within a building – similar in layout to ducted air conditioning, with ducts & vents placed in important rooms like bedrooms & living areas, and return ducts in corridors & other less-used spaces.

So how does it work?

HRV exchanges the temperate indoor air past the incoming outdoor air to transfer the warm air temperature of the interior to the cool incoming air, or cool indoor air to warm outdoor air. (This can be done a number of ways.) In a Passivhaus, the minimum efficiency requirement is 75%, but some systems can transfer up to 94% of the internal heat.

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It is operated by a very low-output extraction fan gently circulating the air - this way it expends minimal energy, and so can run continuously without running up an expensive power bill. Some Passivhaus buildings can rely entirely on this system without the need for additional heating or cooling – using only solar heat gains through windows, and surplus internal heat gains from occupants and appliances to heat the atmosphere. This is one of the principles that make it an almost “passive” system by being so efficient.

It also filters outdoor air through high-quality filters, and controls humidity which keeps mould growth down. This is probably the most important aspect of the way it works within an airtight system to create fresh air-filled spaces. This ensures the occupants have access to clean, fresh, low-carbon air year round, with help of an air quality monitor. This makes it a great system to use for those with hypoallergenic or respiratory conditions.

Whether you’re looking for the Passivhaus standard or simply a high-functioning home, an MHRV system is definitely something to consider to get you there.