ᐅ Jamb Ventilation – How Large Should the Air Gap Be?

Hello everyone,

We have installed a controlled residential ventilation system Wolf CWL 400, and I want to create a transom ventilation horizontally, above the door leaf.

How many millimeters do I need to mill out over a length of 80cm (31.5 inches) to allow the required air volume to pass through? Is there any calculation formula for the air cross-section?

The gap under the door is sufficient in 16 out of 17 cases.

I would prefer not to be the 17th case. What is the formula to check this?

As a general rule, if 50% of the pipe’s cross-section fits under the door, there will be no issues. Depending on the system, this corresponds to a gap of 2-3mm (0.08-0.12 inches).

Door leaf with seals.

Door width > A 600 mm (24 inches) - B 700 mm (28 inches) - C 800 mm (31.5 inches) - D 900 mm (35.5 inches) - E 1000 mm (39 inches) - F 1200 mm (47 inches) - G 1400 mm (55 inches) - H 1600 mm (63 inches)

@Mycraft
This is exactly what I was looking for. Thanks a lot!

In my specific case, I have 90cm (35 inches) doors and a maximum air volume flow of 45m³/h (26.5 cfm). So, I need a gap of 13mm (0.5 inches). Assuming that 2–3mm (0.08–0.12 inches) are already accounted for by normal installation, I would make about 1cm (0.4 inches) with the door frame ventilation.

Is this okay? Can I generally assume 1cm (0.4 inches) for all door frames, or should I actually go room by room and adjust the slots accordingly?

@Lumpi_LE
But the diagram contradicts your statement now.