clinresga

vent hoods and noise: the real scoop on vah!

clinresga
September 24, 2008

OK: I've been following with great interest keitel's post on VAH hoods and noise. I'm in his camp: our VAH is noisy as all get-out. Others including shannonplus2, juliet3, and john.com have disagreed, arguing that their VAH's are "almost unoticeable on low" to quote john.

So, I figured, time to get some objectivity into this discussion (excuse my ego, but I started a new post cuz I think this is of general interest and worried it would get lost in a VAH post).

I pulled out my trusty Radio Shack SPL meter, normally used to calibrate the home theater, and took some readings (measuring from ear level when standing at usual cooking distance from range):

Our Vent a Hood 42'' 600 cfm hood liner at the lake:

65 decibels at low

67 decibels at high

Our Modern-Aire 64'' (1200 cfm) hood liner with remote inline Fantech FKD 10XL blower and LD10 silencer at the main house:

60 decibels at high

What does that mean? Well remember decibels are a measure of sound energy on a log scale. Thus, a three decibel increase represents a 10-fold increase in sound energy. Thus, 67 db represents about a 100-fold higher sound energy level versus 60 db.

A more useful way of comparing these noise levels would be to reference them to everyday sounds. Here are some examples:

60 db: "normal conversation"

[Ref: http://www.howstuffworks.com/question124.htm]

60 db: "conversation in quiet living room"

[Ref http://www.epd.gov.hk/epd/noise_education/web/ENG_EPD_HTML/m1/intro_5.html]

In contrast:

65 db: "average road traffic at 25 meters from busy primary distribution road"

see www.epd.gov above

67 db: level of noise that Caltrans feels justifies construction of a soundwall by an existing freeway

Ref: http://www.dot.ca.gov/dist07/resources/soundwalls/samples/synopsis.htm

69 db: the sound of loud snoring

70 db: vacuum cleaner at 10 feet

Ref: http://trace.wisc.edu/docs/2004-About-dB/

That's a fancy way of saying that the VAH is way noisy, and the MA/remote blower is very quiet.

Could it be our ducting making our VAH noisy? Doubt it, since as I posted before it's a straight shot up from the hood directly into the attic (it's a one story house) and out the roof through 10'' ductwork. Could we have an unbalanced blower? I guess, though both of the two 300 cfm blowers in the VAh are equally noisy and I'd be surprised if they were both defective.

Bottom line: this is an apples and oranges comparison. There is no way that it's fair to compare our inexpensive VAH to the very high end Modern-Aire liner/Fantech blower and silencer combo, and I'm not disparaging the VAH hoods, which obviously many folks have had a good experience with.

I do think though that this reinforces my belief that if:

1) you want high cfm ventilation

2) noise is a major concern

3) cost is not a primary issue

then remote blowers, preferably with silencer, are clearly superior.

Just my obsessive 2 cents worth :-)

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