The function of ventilation is to handle three things

• Human
• Construction
• Wallet

Many people suffer from indoor air quality problems in old houses without even realizing it. When I talk to them, I often hear things like, "We haven't noticed anything, we haven't had any symptoms, we sleep really well, this house breathes, we open the windows, we've managed just fine for this long, people managed fine in the old days, we have cubic meters to breathe here, our fresh air comes from the sauna, etc.". 

This is how it's done, as it's always been done, or is it?

However, while touring old houses, I often had to notice deficiencies in their ventilation.

In gravity ventilation, the building's ventilation relies on the pressure difference caused by the temperature difference between outdoor and indoor air and wind. Supply air, or replacement air, vents are located in the exterior walls of living spaces, window frames, or ventilation hatches. Exhaust air vents are in so-called dirty areas like restrooms, bathrooms, and closets.

Principle of operation of a gravity ventilation system: Fresh outdoor air enters the living spaces of a dwelling through supply air vents, and the air exits through exhaust air vents in the utility areas into exhaust ducts due to the pressure difference.

Starting the oven in the summer heat?

The weaknesses of gravity ventilation are air exchange, especially during summer heatwaves, high energy consumption, and the feeling of drafts.

Drafts are felt near the replacement air vents as cold replacement air flows into the building. Drafts are also felt if replacement air is not systematically arranged. In that case, the building draws the necessary replacement air uncontrollably from between the structures, which often results in cool floors and drafty corners. Of course, in this situation, impurities are also carried from the structures along with the replacement air flow.

Does air move on its own?

The problem with gravity ventilation is that airflows vary due to changes in weather conditions. Ventilation is most effective in cold and windy weather. In warm and windless weather, ventilation is non-existent. In the exhaust duct, air may sometimes even flow in the wrong direction, causing odor and dust problems indoors.

Ventilation can also be enhanced by installing wind-powered draft enhancers or wind deflectors at the end of the exhaust duct. Nowadays, so-called fan-assisted gravity ventilation is also used. In fan-assisted gravity ventilation, a fan is added to otherwise gravity-based ventilation to achieve sufficient airflow.

The above-mentioned system generally causes significant negative pressure, and it is impossible to balance the amount of make-up air with the exhaust air.

Remnant of ancient history

Until the 1960s, residential buildings had almost exclusively gravity ventilation. Today, gravity ventilation is no longer commonly favored because it does not provide adequate ventilation to all rooms. It is also not an energy-efficient system.

Energy prices are rising, should I heat the magpies or my home?

People shop around for electricity plans, try out electricity from the exchange and off-peak electricity, but what if energy were reused?

Energy consumption is also higher in gravity ventilation compared to a mechanical supply and exhaust ventilation system. This is because the heat energy of the exhaust air cannot be recycled back into the supply air, but is directly released outside.
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How is ventilation handled nowadays?

Nowadays, nearly all new apartments and single-family homes are equipped with a mechanical supply and exhaust ventilation system. In mechanical supply and exhaust ventilation, air is blown in and removed through the system. The advantage of this system is that airflow can be precisely controlled, ensuring continuous and consistent air exchange. The incoming air can be heated before it is blown into the space. The heat energy recovered from the exhaust air is used to heat the incoming air, meaning the system is also energy-efficient.

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But you can't install mechanical ventilation in an old house, can you?

This is a common—and actually quite reasonable—idea. A standard heat recovery ventilation system generally operates continuously under a slight negative pressure. Why? Because positive pressure would shift the dew point of the air into the walls of the building, causing moisture damage. New homes are built to such a high standard of airtightness under strict building codes that negative pressure cannot draw replacement air through the building envelope. 

What kind of ventilation is suitable for an old house?

Fresh’s room-by-room HRV system is specifically designed as a breathable solution for older homes. We are able to maintain a controlled supply and exhaust airflow at a constant pressure, ensuring that the same amount of air is brought in and removed, preventing negative pressure from developing. In addition, thanks to HRV technology, we can supply replacement air that is warm and draft-free year-round.
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The need to boost ventilation can be determined with indoor air measurement, whose results can determine the scope of the required actions. Order a free indoor air measurement.

Sources:

• www.hengitysliitto.fi
• https://www.tiede.fi