How does the ventilation system work in a passive house?

María Eugenia Velásquez

March 16, 2022
Young woman sitting in armchair taking deep breaths

I have been wanting to do an article on the ventilation system of a passive house for some time, mostly because it is a key aspect of Passivhaus construction but most of the information that can be found about it tends to be very technical.

That's why I've tried to break it down into 5 basic questions that you as a future passive house owner might be asking yourself.

1. Why do passive houses have a ventilation system?

The answer to this question is very simple: so that you don't have to open the windows to ventilate. OK, this doesn't mean that you can't open the windows, but the idea is that it shouldn't be the main source of ventilation in your house. Because all the effort that has gone into keeping the indoor temperature comfortable passively goes down the drain when you open the window. 😅

2. How does this ventilation system work?

The ventilation system is very well thought out, what it does is to bring outside air into some rooms of the house, such as the bedrooms and the living room. This air then passes through a filter to remove impurities and pollutants. And here's the really cool part - it draws air from rooms in the house that tend to generate higher humidity and odours, such as the kitchen and bathrooms, and exhausts this air to the outside.

This graph from the Passivhaus Institute can help you get a better idea:

3. What is a heat recovery ventilation system and what is it for?

To improve their energy efficiency, Passivhaus buildings must have a ventilation system with heat recovery. This system not only circulates and filters the air, but also helps to maintain a comfortable indoor temperature. By recovering heat from the air extracted from the kitchen and bathrooms, and transferring it to the fresh air coming in from outside.

This system is able to transfer up to 90% of the heat from the extracted air, so it serves as a kind of "heating" because the air coming in from outside reaches the rooms and the living room almost at room temperature.

Important! During the summer there is no need for heat recovery, so the system includes a summer bypass option that disables this function.

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4. What are the benefits of having a ventilation system in your home?

- Fewer allergies and respiratory diseases. As the outside air passes through a filter, pollutants, pollen and dust that cause allergies and respiratory illnesses will not enter your home.

- Less humidity. The air that is extracted from the kitchen and bathrooms helps to eliminate the humidity that is produced in these environments, thus preventing the formation of mould and mildew.

- Less unpleasant odours. Yes, by maintaining constant air circulation, odours are also extracted.

- Reduced need for heating. The heat recovery unit will transfer as much heat as possible to the incoming air and this reduces the need for additional heating.

5. What maintenance does a ventilation system require?

The maintenance of a ventilation system is very simple. The main thing will be the change of filters, which can be between 1 and 4 times a year. The frequency of filter changes will depend on where the house is located, as the air in the city is not the same as the air in a rural area.

You may also consider contracting regular check-ups with the manufacturer to help prolong the life of the ventilation system.

Bono: Is the ventilation system noisy?

No! The ventilation systems you can find on the market today are almost imperceptible. The sound they generate cannot exceed 25 decibels, which is equivalent to the noise in a library or any room with quiet people, or the rustling of leaves in a light wind.

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Source: "Active for more comfort: Passive House", International Passive House Association.

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