Why your airtight building needs mechanical ventilation with heat recovery

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Why your airtight building needs mechanical ventilation with heat recovery

If you’re using our method of constructing energy-efficient buildings, or indeed any other method that creates an airtight shell, you must install a ventilation system.

We find that most people don’t initially like the sound of this! But bear with us and we’ll explain what it is and why it’s essential.

What is a mechanical ventilation system?

Simply put, it’s a system of air pipes throughout your building, linked to a heat exchange system. It ensures there’s always clean, fresh air inside and it also manages excess moisture. Its ability to capture heat is central to how a Passivhaus works.

Why you need one in an airtight house

  1. Heating

When you use a building, you generate heat and moisture during everyday life – from appliances and cooking, for example. The idea behind an energy-efficient, airtight house is that it captures this warmth, using it to heat the fresh air brought in from outside. Indeed, that’s one of the main reasons why this type of building costs less to heat. By re-using heat that’s naturally created in the home, you reduce the demand on whatever other heating system you may have, whether you’ve opted for a biomass boiler, ground/air-source heat pump or gas, for example.

Your mechanical ventilation system draws in air from your rooms, captures the heat from it and then expels it, bringing in fresh air that’s warmed using the heat captured from the expelled air. It maintains a comfortable temperature all year round with minimal use of other heating sources.

‘You should view your ventilation system as the lungs of your energy-efficient house and it’s one of the essential components of a Passivhaus. To quote the Passivhaus Trust website:

  • “To achieve the Passivhaus Standard in the UK typically involves:
  • very high levels of insulation
  • extremely high performance windows with insulated frames
  • airtight building fabric
  • ‘thermal bridge free’ construction
  • a mechanical ventilation system with highly efficient heat recovery
  • accurate design using the Passive House Planning Package (PHPP)


Moisture control

Your ventilation system also performs another really important job: it controls moisture in your building. One of the great benefits of an airtight, energy-efficient building is that you won’t suffer from the problems of damp, mould and condensation.

Your building works as a system to achieve this, your heat-recovery and ventilation system is at the heart of it. It draws in air from inside your house as well as fresh air from outside, removing excess moisture before circulating it around the building.

Your timber-panel frame is the other component in your building that reduces the possibility of condensation and mould. Condensation happens when warm, moist air (like you have inside your house) touches a cold surface. Our timber panels are highly insulated, so all the coldness from outside stays on the outside of the panel, meaning there isn’t a cold surface on the inside for moisture to condense against. Meanwhile, they have a vapour barrier that stops moisture in the air inside the house from travelling through the panel and condensing against the colder exterior side of the panel.

You often hear about people moving into new houses and immediately having problems with condensation and mould. That’s often because there hasn’t been enough attention to ventilation.

One of our suppliers of airtightness materials, Ecological Building Systems, sum it up quite well: “Build tight, and ventilate right.”

By |2017-03-05T13:48:40+00:00February 18th, 2016|Moisture control, MVHR, Passivhaus|0 Comments

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