ᐅ Sizing of the Exhaust Duct for the Range Hood

Hello,

I am currently considering the appropriate size for the exhaust duct of the range hood.
Based on my research, I found a table from Miele that recommends duct sizes depending on the airflow capacity of the hood:

Ø 100 mm (4 inches) up to 300 m³/h (176 CFM)
Ø 125 mm (5 inches) up to 500 m³/h (294 CFM)
Ø 150 mm (6 inches) up to 800 m³/h (470 CFM)
Ø 200 mm (8 inches) up to 1800 m³/h (1060 CFM)

Our range hood operates at 270 m³/h (159 CFM) in normal mode and 420 m³/h (247 CFM) in intensive mode.
Accordingly, we probably need a 125 mm (5 inches) duct.

If the duct is too small, the airflow noise is said to be higher because too much air is forced through too narrow a duct, which causes noise.

Now I wonder what the effects would be if I installed a 150 mm (6 inches) duct anyway:
- Would the noise level be even lower?
- Would it be less efficient in terms of energy? (We are installing the Weibel "Mauerkasten," which is supposedly 100% airtight against air, wind, and water.)
- Any other negative impacts?

Thank you very much for your advice.

Hello.

A larger diameter has no negative effects. A proper wall box is sealed and complete. Also, there apparently are no wall boxes in 125 mm (5 inches). Even Miele only offers a 150 mm (6 inches) model. Technically, the airflow capacity will always be higher in a larger duct, since the pressure loss decreases as the flow velocity drops.

The cover flap from Weibe is pipe-independent. It fits pipes up to 160 mm (6.3 inches) in diameter because it is simply "slipped over" them.

Knallkörper schrieb:
Technically, the airflow in a larger pipe will always be higher, as the pressure loss decreases with lower flow velocity.

My understanding is that because the pipe is larger, the extractor hood will also move more air outside, as it is easier for the hood to transport the air out while maintaining the same power consumption.
Or in other words, with a larger pipe, I could potentially run the hood at a lower setting and still transport enough air outside. This in turn would lead to a quieter hood during operation.
Is that correct, or completely wrong?

Kaspatoo schrieb:
The cover flap from Weibe is independent of the duct size. It fits ducts up to 160mm (6.3 inches) because it simply slips over them.

I understand it as follows: since a larger duct is used, the exhaust hood will move more air outside because it is easier for the hood to transport the air out while maintaining the same power consumption.
Or in other words, with a larger duct, I could possibly run the hood at a lower setting and still transport enough air outside. This in turn would result in a quieter hood operation.
Is that correct or completely off?

Well. I would rather buy a wall box that matches the duct and can be sealed against it. Otherwise, you’ll end up with a perfect breeding ground between the base plate and the facade. On Weibel’s entire website, there is no information about the diameter of the outlet opening. For that reason alone, I wouldn’t buy it.

A larger duct (150 mm / 5.9 inches instead of 125 mm / 4.9 inches) does lead to higher airflow, but probably has less impact than changing the speed setting on the hood. Unless your duct is very long, then the diameter has a greater influence. After all, a 150 mm (5.9 inches) duct has a cross-sectional area that is 44% larger than a 125 mm (4.9 inches) duct.

The fact is: Larger duct = less noise + more airflow at the same setting.

Knallkörper schrieb:
Well. I would rather buy a wall box that fits the pipe and can also be properly sealed. Otherwise, you’ll end up with a great habitat between the base plate and the facade. On the Weibel website, there is no information about the diameter of the outlet opening. For that reason alone, I wouldn’t buy it.

I found information on the website stating that pipes up to 160mm (6.3 inches) are supported.
Why would anyone want to preserve a habitat like that?
Why wouldn’t such a habitat form with “complete” wall boxes?
I consider the biological conditions the same, whether it’s just a base plate or a projecting box. Previous experience reports have not mentioned habitats like that, so it seems more like your assumption, right?

Higher air volume means more warm air is lost, which is an energy disadvantage.

Is the Miele chart reasonably accurate in saying I would need a 125mm (5 inches) pipe, or does anyone have a differing opinion?

Kaspatoo schrieb:
Why should a biotope be preserved?

Because exhaust air can flow between the foundation slab and the exterior wall and condense there.

Of course, higher air volume results in more heat loss. But air volume is what you want after all. Otherwise, if every cent in heating costs matters to you, you might as well buy a recirculating hood.