Uncovering the Science Behind Noisy Oven Fans

[T.O.E Dream]

What causes a fan, most often the one on top of a stove to be so loud when turned on?

I mean is it the air moving or the motor?

 

[Emc²]

Extractor fans normally cause vibration in addition to the motor/fan noise so...

Solution = Open a window / door when cooking or...

Get a take away.

^trying to be funny. :D

 

[FredGarvin]

The more air a fan has to move, the louder it is going to be unless it is a highly engineered fan. A stove top vent fan does not fall into that category.

 

[vibjwb]

Is this an exhaust fan?
An exhaust fan does not have a noise barrier.
The bearings in the fan motor could wear out causing the noise.
A high output motor can cause a lot of high noise because of air movement.
Has the noise got higher lately or has it always been there?

 

[T.O.E Dream]

No, it's not my oven fan I'm worried about but I'm talking in general.

 

[russ_watters]

The exhaust ductwork on such systems (if it even exists) is almost always undersized and undersized ductwork makes for noisy systems.

Oftentimes, though, it isn't an exhaust fan, it is just a recirculating fan and a filter.

 

[crx]

Because of the water vapors (humidity) that makes the air more dense ,and creates more turbulence around the blades...just like an aircraft cuts into the clouds you can hear a chance in the engine frequency and increased wing vibration...I'm just guessing of course )

 

[sophiecentaur]

Because of the water vapors (humidity) that makes the air more dense ,and creates more turbulence around the blades... . . )

In fact, humid air is less dense than air with no water molecules. The molecular mass of H2O is less than that of O2 and N2 and there are the same number of molecules (total) per unit volume at any given pressure. This is a popular misconception - along with "Air is like a sponge".

The reason why many fans are noisy is that they try to make them as small as possible and, hence, the speed of air passing through needs to be relatively high, with a consequent amount of turbulence / noise generated by the fan blades. Also, the blades may be a really naff design and not necessarily suited to the application - just suited to the accountant at the factory.
I am always impressed by the low noise level that you get in the bathrooms found in some hotels and blocks of service flats. The extractor will be a large one, situated remotely on the roof, which goes round at relatively low revs. You can do it if you try!

 

[crx]

In fact, humid air is less dense than air with no water molecules. The molecular mass of H2O is less than that of O2 and N2 and there are the same number of molecules (total) per unit volume at any given pressure. This is a popular misconception - along with "Air is like a sponge".

you are completely right but i think that water will saturate the air rather than diffuse at a molecular level (above a stove for example or in the bathroom) and will form microscopic droplets of millions of molecules which at that level will have a higher density than dry air.

 

[turbo]

We have a Broan recirculating range-hood that is very quiet at the low setting, BUT it doesn't remove smoke and fumes very well on that setting. To get good air-movement, you have to use the high setting, which is lots quieter than our old hood was, but still a bit noisy. With the twin halogen lights, two-speed fan, two-intensity lamp intensity switches, the price was more than I really wanted to pay, but the brushed stainless with black trim matched the new Electrolux range nicely and my wife loves them. I would hate to have had to pay for a larger, more effective fan with better isolation and sound insulation. I've got to feel that there is a price-point that hood manufacturers try to meet, and since hoods are usually operated intermittently, noise-reduction is not high on their list lest they lose customers to less-expensive models.

 

[sophiecentaur]

crx
You have a point about the droplets.

 

[Intelligent-E]

Not enough technology or time either money to make them so they wouldn't make so much noise.
But they can actually change that "bug" if it can be called that way.

 

[sophiecentaur]

crx
You have a point about the droplets.

And the oil / fat molecules which are very much more massive and which soon will coat the blades and increase drag and turbulence.

 

[crx]

crx
You have a point about the droplets.

...I love you too!