ᐅ Ventilation with Mechanical Ventilation Systems

Here’s my input as well: We built our house last year and moved in December. None of us had any experience with a mechanical ventilation system with heat recovery. Throughout the entire winter, we never felt the need to open a window, which was really very comfortable, and despite keeping the windows closed, there was always a feeling of fresh air. At times, my wife found the humidity a bit too low (~30%), but I’m not sure if that was connected to the mechanical ventilation system—it might not have been related at all.

Then came summer: We have very large window areas on the south side, and it’s easy to underestimate how much heat these add, even with triple glazing. Indoor temperatures rose to 25-26°C (77-79°F). We overestimated the effectiveness of the mechanical ventilation system for cooling (specifically the bypass function and the use of cool night air). In our case, it only lowered the temperature by about 0.6°C (1°F) overnight at best, and you end up "heating" the house yourself with your own body heat. For summer, we switched to keeping the roller shutters (external blinds) closed during the day and setting the ventilation system to its minimum level to avoid stuffy air. Classic cross-ventilation in the evening is simply more effective for cooling; even with the bypass, the outside air warms up again as it passes through the house.

Our personal conclusion: Mechanical ventilation with heat recovery is great and we would definitely install it again, but during summer it plays a minor role.

How does a system like this perform in a bedroom with two people? Should you expect drafts or poor air quality?

No, there is no need to worry. Of course, one could set their mechanical ventilation system so high at night that it might cause drafts, or so low that practically no air exchange happens, but no one would do that.