ᐅ Which pressure switch should be used to shut off the mechanical ventilation system with heat recovery?

We have a mechanical ventilation system with heat recovery, recirculation, and a room-air-independent fireplace. The fireplace seller shifted the decision regarding the pressure switch to the local chimney inspector. According to him, of course, it wasn’t needed.

In the electrical tenders, neither procurement nor installation wanted an electrician to handle it, as if it was completely new territory.

Fortunately, our mechanical ventilation system (Zehnder ComfoAir) has an emergency shut-off, and the chimney inspector had just attended a training course at Zehnder and was aware of this.

Therefore, we do not need a pressure switch.

I believe the chimney inspector was as relieved about this as we were.

Hello,

we also have a mechanical ventilation system with heat recovery, a recirculating cooker hood, and a DIBt-certified soapstone stove.

When our home builder brought up the topic of differential pressure switches, we contacted our local chimney sweep and provided him with all the technical details regarding the mechanical ventilation system, the recirculating hood, and the stove.

He reviewed everything and informed us that a differential pressure switch is not required.

The key points for him were:

- The stove has an automatic locking mechanism
- DIBt certification
- The mechanical ventilation system is adjusted to maintain a slight positive pressure inside the house

As @Sebastian79 already mentioned, however, there is no guarantee that you won’t need a differential pressure switch if these points are met – the final decision always lies with the local chimney inspector.

Therefore, I also recommend involving this person early in the process and obtaining their decision in writing.

Best regards,

Dirk

From a construction perspective, positive pressure is actually rather problematic – if there is any leak, it pushes moisture into the insulation. Just a quick FYI...

Thank you, but the lively discussion doesn’t really help me move forward for now.
Since the stove will be installed later, I can’t show anything to the chimney sweep yet. So, it’s mainly about what I need to prepare for a possibly required pressure switch.

@Sebastian, can you tell me which switch you have?

The P4 standard – but today I would choose a version that includes an output for a notification.

@Sebastian79 : You are not entirely wrong. However, this only applies to a theoretically 100% airtight "box." The minimal "overpressure" will always find the path of least resistance, and in my opinion, that is still the numerous exhaust vents of the controlled residential ventilation system.