ᐅ Does the ventilation system really pump humid outside air into the house?

Good evening,

I need the help of this great forum again. I searched online beforehand but couldn’t find anything. So, I’m trying here:

We have a single-family house built in 2021. The ventilation system provides a very comfortable indoor climate. We feel good. However, my hygrometers show quite high humidity levels (in the basement 70% / in the living area just over 60%). On one hand, I find this worrying, but on the other hand: the ventilation system brings outside air inside, and currently, the outside humidity is over 70%. So, you could say: no wonder! If that’s true, I don’t understand the purpose of the ventilation system if it’s blowing humid outside air into the house.

Thanks for clarifying where my thinking is wrong…

Have a nice evening
Daniel

This is how ventilation systems usually are: too humid in summer, too dry in winter – ideally, there should be a so-called "humidity recovery" feature integrated into the system that operates during winter. But what about in summer? This humidity recovery function is available in some systems or can be added as an upgrade module. Then you can also set the system to run more at night in summer and more during the day in winter.

Do you have heat recovery as well, meaning a heat exchanger included? That might help to some extent.

But generally, the main purpose of the ventilation system is: to bring in fresh, oxygen-rich air and remove used, oxygen-poor, and odor-laden air.

Thank you for the quick reply.

Yes, we have heat recovery ventilation. It works fine so far, but unfortunately, it doesn’t have any effect on humidity.

Now I’m considering running a dehumidifier in the basement occasionally during the summer. Kind of a silly idea, though.
On the other hand, the relatively high humidity might not be that critical since the ventilation system does remove potential mold spores.

Oh, it’s all quite complicated…

Schubbiano schrieb:

I don’t understand the purpose of the ventilation system,

Well, the purpose of the system is actually in the word itself: VENTILATION. Nothing more, nothing less. It’s not a comfort air temperature and humidity control system ;-)

In summer, it’s basically like having an open window equipped with a fan (and, of course, a nice pollen filter in between). If you want dry air inside, you need to buy a dehumidifier or an air conditioner.

P.S. You have to distinguish between relative and absolute humidity. If it’s 16°C (61°F) outside at night with 80% RELATIVE humidity, when the air comes inside at 22°C (72°F), the relative humidity drops to only 63%.
In winter, it’s the opposite. If it’s -10°C (14°F) outside with 45% humidity, when it comes inside to 22°C (72°F), it corresponds to about 5.5% relative humidity (yes, that’s just a theoretical value). That’s why indoor air is always dry in winter with a mechanical ventilation system without humidity recovery.
In both cases, the absolute amount of water per cubic meter of air is exactly the same.

Addition: The moisture recovery module for winter is called an "enthalpy heat exchanger."

It is even more important to understand when humidity really becomes a problem.
This occurs primarily, or actually only, when the dew point is reached or passed anywhere in the apartment or house, usually on exterior walls. In that case, the warm, moist air condenses, causing the wall or the back of a cabinet to become damp and mold to develop.

As long as the dew point is not reached, which is almost impossible to happen during the summer, there is no issue with mold growth.

However, you should run your ventilation system at the lowest setting during the day in summer, especially in the peak summer months. Because along with moisture, you also bring warm air into the house. The heat exchanger can barely prevent this.
At night, switch the system to the "summer ventilation" mode (that’s what it’s called in my system). This extends the cycle from 45 seconds intake and 45 seconds exhaust to 1 hour intake and 1 hour exhaust, bypassing the heat recovery. This way, you bring cooler night air into the house.