# rooftop grease exhaust fans



## william sparky (Jan 30, 2010)

i need to install liquid tite flex or teck cable for a 3 h.p. commercial kitchen exhaust fan on a flat wooden roof. i want to know the correct way to penetrate the roof for the cable. the cable will be #12 3 wire.


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## BurtiElectric (Jan 11, 2011)

how about a pitch box?


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## McClary’s Electrical (Feb 21, 2009)

I use this and a pvc weatherhead. I cut the hole right beside a truss and use two hole straps on the truss.


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## ohiosparky99 (Nov 12, 2009)

Anyway to come up inside the curb under the fan??


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## B4T (Feb 10, 2009)

I get a pitch pocket made.. bring the flex through it.. spray foam the inside.. and cover exposed foam with roofing tar after it dries..


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## McClary’s Electrical (Feb 21, 2009)

ohiosparky99 said:


> Anyway to come up inside the curb under the fan??


 
Don't make any wiring preparations until you see the fan. I've seen them come with threaded conduits going through doublewalled ducts.


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## ohiosparky99 (Nov 12, 2009)

mcclary's electrical said:


> Don't make any wiring preparations until you see the fan. I've seen them come with threaded conduits going through doublewalled ducts.


True, alot of times we come up through the curb, stub out the side of the curb to a WP bell box w/ disc then sealtight to the motor if possible


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## BurtiElectric (Jan 11, 2011)

B4T said:


> I get a pitch pocket made.. bring the flex through it.. spray foam the inside.. and cover exposed foam with roofing tar after it dries..


Me too, but I call it a pitch box


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## chicken steve (Mar 22, 2011)

ohiosparky99 said:


> Anyway to come up inside the curb under the fan??


actually the duct opening should have space , if not a KO for squealtight.....~CS~


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## ohiosparky99 (Nov 12, 2009)

BurtiElectric said:


> Me too, but I call it a pitch box


Pitch pockets are great also, we just try not to make any roof penetrations at all if possible


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## MechanicalDVR (Dec 29, 2007)

I have used Alumi-Flash pipe portals for roof penetrations going back ten years. They can't be beat. http://www.commercialproductsgroup.com/products/rps-accessories/pipe-portal-system/alumiflash.aspx


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## n5i5ken (Jun 5, 2011)

for your roof penetrations, we usually use a "witches hat" and have the roofers then seal around it. We do not do the roof penetrations on our jobsites.


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## Sparky208 (Feb 25, 2011)

You should check with the owner if there is a warranty on the roof. Most flat roofs I work on we have to use the company that installed it to hold the warranty.


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## leland (Dec 28, 2007)

The curb is usually bigger than the duct,sneak in there and then up to the motor.
Avoid your own penetrations.


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## chicken steve (Mar 22, 2011)

i'm an electrician, not a roofer.....~CS~


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## william sparky (Jan 30, 2010)

*rooftop grease exhaust fan*

thanks for the info. i am hoping i can get up between the curb and the duct


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## Amish Electrician (Jan 2, 2010)

DON'T do it!

There are fans, and there are kitchen exhaust fans.

The mechanical code does not allow you to run the wires through the fan, as is common in fan installs. Nor can you run it up along the outside of the ductwork. That's your first problem.

Your next problem is that the fan will have to be removed for cleaning the ducts. OK, I know that the fans are often hinged - but the duct guys typically cut the hinges and set the unit off to the side while they clean. Allow for that.

Typically, I will come through the roof with my own penetration, above the fan. I'll stub up pipe to a box, and have a whip of sealtite to a disconnect switch on the outside of the unit. This arrangement allows the cleaners to set the unit above the duct penetration while they clean, and you to turn off the unit when you replace a belt.


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