Hoods, Noise and Venting Q & A

Q.
At 12:46 PM 9/5/2006, you wrote:

Hi Peggy,
Quick question:
I went to purchase our Viking Range and Hood and was asked and/or told the following so before I purchase, I want to make sure what I order will be accomodated in our kitchen plan.

1- I was told I had to order the 27 inch depth hood. Although, we talked about 24 inch depth.
Do you know of a reason why I should consider the 27 inch?

2- I have a choice between a 1200 or a 1500 CFM external motor for the hood.
Do you have a preference? (Which by the way, I didn't realize that the motor didn't come with the hood. Note to self.)
Thanks for getting back to me as soon as you can.
I would like to place our appliance order in the next day or so.
Hope all is well,
Monica

A.
The 27" deep hood will capture more of the smoke and steam and fumes off of the range than a 24" deep hood would.
A column of heated, greasy, air comes off a pan and spreads 3" in a 30" rise from the pan surface to the hood.

That means a 12" fry pan gives off an 18" diameter plume by the time it gets to the hood.
If there is no hood over part of the column, some of the greasy steam will rise to the ceiling and spread into the room.
There is no such thing as a hood that can capture and pull grease-laden air beyond its overall dimensions.
This becomes a cleaning issue over time.

There are other considerations though...

The height of the user(s) is definitely an issue.

I would hang some cardboard to mock up the bottom of the hood at 66" from the floor, sticking out 27", to see if it is an issue for the cook.
It likely could be...in fact, the 24" deep one could be an issue too.

Another option of course is to hang the hood higher to get it up out of the way.
Viking says we can go up to 72" high (although that is really marginal in my mind...it defies physics).

We already are using a 54" wide hood with a 48" range so we have the capture of the 3" in 30" rise covered on the sides.
If you go with the 27" deep hood we will have it covered in the front.
BUT the column of steam keeps expanding as it rises, so the higher the hood the bigger it needs to be to capture everything.
Raising the hood above 66" will again lose some of the steam in the front.

There is also the issue of venting the hood to the rear, which is desirable in this case.
If we raise the hood, that option likely goes away, since Viking recommends 24" of vertical rise before turning the vent pipe to the rear.
Unless your house has balloon construction (wall studs that go from the foundation all the way up to the roof), we only have about 24" available if the hood is mounted at 66".

I would use the 27" only if it is comfortable (or you can LEARN to be comfortable) using the range with the hood at 66".
If it's not, I would skip it and stick with the 24".

Now, on the hood motor choices:

I strongly recommend an INTERNAL motor for your hood rather than the external ones they want you to buy.
The reason to buy an external motor is touted as the noise factor.
This is a fallacy.

The noise a hood makes is directly related to how it is vented.
This is why I asked you to be sure to read the caveats about hood venting on your appliance specifications.
If you plug in a hood fan without having it attached to the vent and run it, you will find it makes almost NO NOISE.
The noise you hear when it is all assembled and installed is the noise of the air rushing through the vent pipes.

This is why I specify that all hood vent pipes be as LARGE as possible and as STRAIGHT as possible.
And, when turns in the pipes are necessary, that they be 45 and 45 degree turns rather than 90 degree turns.

90 degree turns cause AIR TURBULENCE in the pipes and contribute to noise.
I also specify that the pipes be supported and thoroughly sealed and insulated with pink fiberglass around them.
This is so they do not VIBRATE and create noise.
Vibration and turbulence are what creates the noise that people object to with their hoods.
Such vibration will be there, or not, no matter where the motor is.

Back to the hood motor...which should be 600CFM.

An internal motor pushes the air.
An external motor PULLS the air.
If you ever have a fire on the cooking surface, an external motor will pull the fire up through the pipes.
Cooking fires are the most common fires in the home.
An internal motor with a squirrel cage fan will cut off fire at the motor, so it will not get into the vent pipes.
This is why I recommend internal motors (they are also cheaper).
Safety, economy, nearly-quiet (when properly installed)...What more can you ask?

Share this email with your contractor.
Best,
Peggy