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Jon, Appliance Technician
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Experience:  Appliance Service Technician with 10+ years experience.
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Question on a new range hood. Jenn Air 3 speed high speed is

Resolved Question:

Question on a new range hood. Jenn Air 3 speed high speed is 600 CFM. 8 inch diameter duct coming off unit, instructions recommend continue with 8 inch. My old unit duct transitioned from 8 inch diameter to 4" x 10" to and thru outside wall. If I did my math right at 600 CFM, the 8 inch has 50 square inches of area and a discharge velocity of 28 FPS. The 4x10 is 40 sq inches and a velocity of 36 FPS.

Do I need to be concerned with this difference enough to rip out ductwork and replace?
Submitted: 1 year ago.
Category: Appliance
Expert:  Jon replied 1 year ago.

Jon :

Hello

Jon :

My name is XXXXX XXXXX I am an authorized Whirlpool service tech and I can help you today.

Jon :

Your blower motor being rated at 600 cfm will actually be ok with those specs.

Jon :

+- 10 fps is to specs.

Jon :

you would notice any backdraft of blower motor struggling to force the vented air out if it was not acceptable.

Jon :

Where is the blower going exactly?

Jon :

i know you said that it is to an outside wall, but where?

Customer:

Range hood is going in interior wall approximately 6 ft from outside wall.

Jon :

ok.

Jon :

But it then does go out and up correct?>

Jon :

so it goes approx 6 ft out and about 8 ft up?

Jon :

The use of the 4'' exhaust will do just fine.

Jon :

the smaller hose and venting that you are mentioning is more along the lines of a dryer exhaust hose and not for venting.

Customer:

Up 90 degree transition bend, over one rafter, another 90 and straight out from there.

Jon :

but if you already have it installed and inplace int he wall then it will do just fine. no need to remove and replace with 8"

Jon :

unless like i said you are getting backdraft and blower will not blwo air out.

Customer:

Not 4 inch. 4 inch by 10 inch duct is what existing is.

Jon :

That is ok about the 90 degree angles.

Customer:

Not installed yet.

Jon :

im sorry i thought you said 4"by 10'

Jon :

my fault.

Customer:

I may have typed that.

Jon :

how did it go from 8" to 4"x10"?

Jon :

if the unit is not installed yet, then yes, I would recommend using the 8" venting all the way through. It is not too hard to do if the unit is not in place yet.

Customer:

The first 90 degree bend is 8 inch on one end and 4x10 on other

Jon :

just get yourself the 8" venting and remove the older smaller portion of the venting and replace with the 8". this way you can be sure the unit is installed to specs.

Jon :

ok, gotcha. I assume the 4x10 is going out of the house then, correct?

Customer:

yes

Jon :

That should work ok. just after install check that the force of air out of the vent outside is blowing good.

Customer:

will do and thanks. Back up plan if an issue is I can replace in future from attic space. Also it is a 3 speed fan.

Jon :

The smaller vent actually gives you more footage clearance so you should be good.

Jon :

yes. that works.

Jon :

Please let me know how you do. and if you need more help i

Jon :

will be here for you.

Customer:

Thanks much for the help.

Jon, Appliance Technician
Category: Appliance
Satisfied Customers: 3508
Experience: Appliance Service Technician with 10+ years experience.
Jon and 6 other Appliance Specialists are ready to help you
Expert:  Jon replied 1 year ago.
Jeff,

Thank you again for the positive rating and very generous bonus. It is greatly appreciated.

Should you have any other questions and or concerns please get back to me here and i will help you more for no additional charge.

Thanks again.

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