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Old 12-28-2007, 04:49 PM   #1
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Inline Duct Fan


I have a range hood that pulls 250 CFM, and exits through the roof. The duct is 7" stove pipe that pokes into the attic. Then it is flexible aluminum to the roof discharge vent. I want to install a inline duct fan that pulls 500-600 CFM at 8" duct. I will have to change to 8" (reducer) to install the new fan. No problem there. I will install the inline duct fan where the stove pipe and the flex duct meets.
Should I leave the existing range hood fan in place and let the inline duct fan help it or should I remove the existing range hood fan. The existing fan is very noisey on high speed. I am concerned that the inline duct fan will make the existing range hood fan turn much faster and cause it to act like a generator, possibly tripping the breaker.
So, should I leave the existing fan in the hood or take it out?

I am a master electrician by trade so the wiring will not be an issue.
Also, The fan I plan to use is made by "Fantech". Is anyone familiar with this brand?

Thanks in Advance......John Valdes

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Old 12-28-2007, 08:22 PM   #2
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Fantech makes very nice fans, but be certain that its specified for your application. Understandably, you want to move as much air as possible from the cook area, but do consider, your not merely moving air. Be prepared to spend some time cleaning this type of fan blade (squirrel cage). If it were dirt or dust, no problem, but once grease accumilates... Provide an access or make it easy to get to for removal and cleaning.
Personally, I'd find another solution.










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Originally Posted by J. V. View Post
I have a range hood that pulls 250 CFM, and exits through the roof. The duct is 7" stove pipe that pokes into the attic. Then it is flexible aluminum to the roof discharge vent. I want to install a inline duct fan that pulls 500-600 CFM at 8" duct. I will have to change to 8" (reducer) to install the new fan. No problem there. I will install the inline duct fan where the stove pipe and the flex duct meets.
Should I leave the existing range hood fan in place and let the inline duct fan help it or should I remove the existing range hood fan. The existing fan is very noisey on high speed. I am concerned that the inline duct fan will make the existing range hood fan turn much faster and cause it to act like a generator, possibly tripping the breaker.
So, should I leave the existing fan in the hood or take it out?

I am a master electrician by trade so the wiring will not be an issue.
Also, The fan I plan to use is made by "Fantech". Is anyone familiar with this brand?

Thanks in Advance......John Valdes

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Old 12-29-2007, 12:23 PM   #3
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My options are limited undone. I can buy another hood with a higher CFM and it has double squirrel cage fans installed or buy the inline. The new hood is $375 and the inline duct fan is under $100. I don't want to mount a roof fan as it will be much more difficult. If the fan is in the attic it will not be as noisey, and pull more air. I just wanted to know if I should remove the existing and let the inline fan do all the work?.......Thanks John

ps.....total lenght of duct is 10'
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Old 12-30-2007, 09:09 AM   #4
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Yes you should remove the first fan. But most importantly a better fan will end up pulling more grease into the exhaust ducting and if you use a fan not intended for that purpose you may end up with a very dangerous fire hazzard. Be smarter than what your working with.
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Old 12-30-2007, 01:11 PM   #5
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bigMike,
Agree. I was thinking the same thing. I have checked the existing duct and it is very clean. So is the motor and existing fan. I have two wire mesh filters at the hood. They look as if they are doing a good job of catching the grease. I will make sure the fan is rated for the application......Thanks
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Old 12-30-2007, 02:39 PM   #6
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Good luck with the project.
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Old 01-06-2010, 08:30 PM   #7
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DUUUUDE... this is a great idea... I might do this too... my fan isnt loud, but I swear it doesnt "suck"

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Old 01-06-2010, 09:22 PM   #8
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The problem that I see with this is that if you pull 600 CFM out of the house you have to replace it some way. Air will find the easiest path into the house such as the furnace and water heater flue or a fireplace chimney. These could be potential to bring carbon monoxide into the house. If you have no gas appliances or fireplaces then in will bring air into the house most likely from you attic or windows and doors.

It is code here that when there is any range hood over 300 CFM then fresh air must be brought into the house and interlocked with the hood and blower on the furnace.

It is not a good idea to put your house in a negitive pressure.

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