Kitchen Exhaust

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I have a kitchen exhaust question that I hope you can help answer!

We recently purchased a home and it has a ducted range hood (Broan Allure 250 CFM or so model) connected to a duct that goes through the kitchen ceiling through the attic and connects to an exterior exhaust fan mounted through the sidewall of a dormer. 

The external fan is wired to the switch on the hood above the stove. The external starts when the hood switch is set to the hi position…and both fans run at the same time.

The external fan motor is: 1/20 HP, HVAC Motor, Shaded Pole, 1550 Nameplate RPM, 115 Voltage, Frame 3.3 

This seems like an unusual configuration to me and honestly doesn’t seem to work all that well. 

1. Is this a common setup? 
2. Would a much higher CFM fan and the exterior fan upstairs work much better?
3. Would you recommend a different configuration?

Any insight would be greatly appreciated!

Thanks so much!

Answers ( 8 )

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    2019-11-21T17:10:35-05:00

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    Thank you – I will. Will have to wait for a warmer day to climb out on the roof

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    2019-11-21T15:59:11-05:00

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    Are you thinking that because it is wired to the fan in the house that it may not be getting enough “juice”? The replacement motor matches what was in that unit originally – The external fan motor is: 1/20 HP, HVAC Motor, Shaded Pole, 1550 Nameplate RPM, 115 Voltage, Frame 3.3

    Perhaps it needs its own electrical and switch?

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      Yes, I would make sure at least 115 volts. Check the suction on that fan by it self. And than to the hood, and see if it’s about the same.

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    2019-11-21T15:50:08-05:00

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    The exterior fan motor is brand new. The housing and fan are probably 25 years old? The hood over the stove is probably 6 or 7 years old?

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    2019-11-21T15:44:27-05:00

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    WOW – that was fast! and thank you so much! There is no flap on the exterior unit – it is a typical external exhaust fan with a dome housing around the blades. You are correct in the length of the run. It is about 40 feet from the stove to the dormer I would say. While I do not believe there is any blockage in the ductwork, I can certainly check.

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      Just luck I guess. I just got home and when on the computer lol. Yes check that. How old do you think the the fan is?

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    It’s common for a long run and that seems to be what you have. I first would make sure you don’t have any obstructions in the line. Do you have a trap door on the outside where it vents out? If so is there enough power to open that vent?