Range Hood Additional Charcoal Filter Air Flow Effect

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Old 09-02-17, 10:35 AM
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Range Hood Additional Charcoal Filter Air Flow Effect

I'm installing a 900 CFM range hood with a very short, straight distance of 6" duct. The manual indicates a maximum run of 50'. I would like to add a charcoal filter (larger than the 6").
1. Are there any disadvantages to adding a Broan CleanAir RF49C (7.5" X 8.5") after the motor?
2. There is good filtering before the motor so it should remain reasonably clean and it is very easy to add a filter after the motor but not before. Are there any advantages (less demand on the motor?) to adding the filter before the motor rather than after?

Any help would be appreciated. Thanks
Jim Brennan
 
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Old 09-02-17, 10:39 AM
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A charcoal filter is only used when the vent hood is used in the recirculate mode. It takes the smells out of the air. Since you are discharging outside.... it's not needed or helpful.

A good mesh screen before the blower is all that's needed.
 
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Old 09-02-17, 10:43 AM
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I don't know who started that recirculation thing. An outside vent is always better, IMO.
 
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Old 09-02-17, 10:46 AM
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The recirculating type are only supposed to be used where it is impossible to run an outside exhaust.
 
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Old 09-02-17, 11:02 AM
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It is impossible to run outside. I would have preferred the outside option, it is simply not available. My choices are no range hood, the tiny unit in place or one at a reasonable price that can help keep grease from gathering on the 16 to 20 foot ceiling and reduce cooking smells in the house. It will never be as good as going outside but it should improve a difficult situation when the snow is piled high on the barbeque and it is exceptionally cold.

Thanks for the quick reply.

Jim Brennan
 
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Old 09-02-17, 11:04 AM
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An exhaust hood gets converted from discharging outside to inside. It should come with all the parts needed to do so.
Where are you going to be discharging that 6" vent pipe ??
 
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Old 09-02-17, 11:13 AM
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Above the stove...the same place the unit would discharge if the 'ductless' option fit and was purchased. There are two layers of filters before the motor, I was just considering adding a third. We looked at a great many range hoods with the ductless option, it can't be that uncommon. It seems people living in high-rise apartment building have no other choice. At least their ceilings don't require scaffolding for regular cleaning.
 
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Old 09-02-17, 11:25 AM
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With a ductless unit.... the recirculated air normally comes out the front of the unit.

So yes.... the charcoal filter over your duct outlet will help control the odors. Most blowers can handle two filters. I wouldn't try for a third.
 
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Old 09-02-17, 11:39 AM
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The recirculation unit for this one was designed to go up as the vented unit would and then out to the sides, not the front. That was not possible in this situation. The unit is designed for a louvered filter system and fifty feet of ducting. I added one layer of charcoal on top of the louvers, which did not appear to change the flow much at all. I then wondered if a second charcoal filter would still put less demand on the motor than the 50' maximum distance of ducting.
I'll try it without the additional filtering and see if the results are satisfactory.

Thanks again,
Jim Brennan
 
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Old 09-02-17, 12:08 PM
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When the filters are clean there will be no issue with flow.
As soon as they start to become dirty the flow will diminish.
 
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Old 09-02-17, 12:33 PM
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Great advice.

Thanks

Jim
 
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