ᐅ Dimension of central ventilation system

We will be installing a central ventilation system from Zehnder. I am considering the "Zehnder ComfoAir Qxxx" model since I will also be implementing a KNX system.
The unit is available in three versions:

- up to 350 m³/h (210 cfm)
- up to 450 m³/h (265 cfm)
- up to 600 m³/h (355 cfm)

The house will have around 170 m² (1,830 sq ft) of living space, and there are currently 3 occupants (another child is possible).
Which of these three units would you choose? Of course, it shouldn’t always run at full capacity, but it also shouldn’t be oversized.

The pressure loss in the pipe network also affects how much the system can actually deliver at different settings. I think the 350 model could work, but it would probably need to run on a high setting, so it’s better to choose a slightly larger size for reserve capacity and potentially quieter operation (you would only notice a difference on the high/intensive setting).

sent from mobile

Same here... for 170 m² (1,830 sq ft), I would also plan with the 450 size. The 350 would probably run at full capacity more often.

Based on the living area, the 350 unit should be sufficient. What air exchange rate is being targeted? What is the building volume? How airtight is the house? I would avoid oversizing.

With controlled residential ventilation, oversizing is not a problem like it is with heating systems, because every controlled ventilation unit can be adjusted continuously. However, “up to 350m³” (up to 12,360 ft³) means that at maximum setting—and usually assuming much lower resistance in the ductwork—this performance is just reached. That means the unit has to be set relatively high for nominal ventilation and truly at maximum for intensive ventilation, which might then become noticeable in terms of noise.

There are regulations regarding the air exchange rate, and the minimum airtightness the house must have is also fixed.

Sent while on the go

Hello,

The argument that a "smaller system produces more noise at a high flow rate" is often mentioned. If the charts on Zehner's homepage are accurate, you don’t need to worry about this. The noise levels for the 350 and 450 systems differ only marginally at the same pressures. The pressures are also determined by the pipe diameters used. In other words, if you simply install a 450 system instead of a 350 system in an otherwise identical setup, you won’t notice a significant difference.

Best regards,
Andreas