having bigger ductwork than recommended in my Wolf rangehood

last year

last modified: last year

I am purchasing a Wolf 42x22 range hood insert with a 1200 CFM internal blower. Reading Wolf's website, I found that Wolf recommends 10-inch ducts. My HVAC installer would like to do 12-inch. The duct will be very short and vent out right behind my hood. I heard that going smaller than recommended is a bad idea, but I do not want to conclude that going with a broader duct is better automatically. It will change the pressure inside the duct. Will that affect the efficiency of the hood negatively?

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Comments (2)

kaseki
last year
Assuming round duct is intended by your HVAC installer ...

Pressure loss will be less, but over a short distance won't matter. The duct is rarely the dominant pressure loss element.

Generally, one wants (particularly in cold climates) to operate between 1000 ft/min and 2000 ft/min. Higher flow velocity means more grease impingement collection in the duct; lower flow velocity means more grease condensation collection in the duct. (Use 2/3 the rated blower CFM as a guess for actual flow, depending on make-up air system.) Over a short distance, I don't think grease collection from either factor will matter. The duct should warm up quickly and the condensation rate will likely be ignorable.

Be sure you have a damper at each end, if space allows, to minimize drafts and wind effects.

Since you asked, efficiency (CFM/watt) will very slightly improve.

I use a 10-inch duct with my Wolf 1500 CFM roof blower and achieve roughly a 1000 CFM.
krisztina_markus7
Original Author
last year
Thank you again, @kaseki. This information gives me peace of mind. I will ask about the damper on both ends; that is excellent advice.
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