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Range Hood Suction

Posted by racmrc (My Page) on
Fri, Jun 29, 12 at 7:10

Just installed a 48" Best range hood with external 1200cfm blower. Used rigid duct, one 90 and one 45 bend with Fantec silencer. Total physical length is 13 feet. System is super quiet.

Question - how much suction should I be getting below the baffle filters. Currently at max speed I feel suction about 6 inches below the baffles and it will hold up a piece of paper as one other person stated as a test. Just trying to find out how much suction other folks hoods have that work good with the woks and grills, etc. Do you have more suction than this or is this normal?


Follow-Up Postings:

RE: Range Hood Suction

I have a 54" Best with a 1500cfm blower outside and what you describe sounds about right. You can test it by getting a skillet really hot and then adding some oil in there to smoke. This is one case where extra virgin olive oil works really well for its low smoking point. Just make sure you give the blower a 5 minute head start to generate a nice circulation. If you don't have makeup air, crack open a window.

In case you find that it's not working well, just lift the pan up toward the baffles as a rescue measure.

RE: Range Hood Suction

Thanks - good to hear its seems about right. Since we are just now redoing the kitchen, we don't have a range yet but I'll find a way to do a similar type test.

Thanks again.

RE: Range Hood Suction

Hoods provide little suction due to flow rate and aperture area. A plot in the ASHRAE HVAC Handbook shows how quickly even the flow rate drops off with axial and transverse distance.

The way the hood works over the cooktop (ideally) is that the rising effluent (which will have an up velocity around 3 ft/min) enters the hood aperture where it is transported by the hood flow rate past the baffles and out of the house. The hood flow rate (and local suction) only need to keep the effluent from reflecting from the hood components and escaping the hood.

If the effluent doesn't directly enter the hood aperture, either due to air turbulence or the hood being too small, it won't be sucked in from the edges except as part of the overall house air that is being entrained in the rising effluent.


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