Can I get some expert advice about sizing hood liner / fan

3 years ago

last modified: 3 years ago

I have really spent a lot of time the past week trying to get my arms around this. Some really great posts by @kaseki and others over the past decade really - with all sorts of great info. But I still have a few targeted questions for the expert air flow guys... All of this in a "typical" 1997 brick suburban home (with really leaky windows)

installing a Wolf Natural Gas range top (SRT366) - 98k total/max BTU

I am really digging a hood like one of these and plan to couple it with an Abbaka XL Pro Liner and the Hy-Ex 1.4 fan mounted on a roof with a 20' slope https://static.appliancesconnection.com/attachments/D55afe7a43eb88.pdf.

The Abbaka XL Pro liner duct outlet is 10", and I plan to add a fantec silencer to the bottom 1/3 of the total exhaust run, which is probably 8-10'

Can anyone suggest a "better" configuration than this concoction I have designed? The liner is significantly more expensive the the Fantec HL42, but also seems to move significantly more air.

Thanks in advance, Jeff

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Comments (3)

kaseki
3 years ago
last modified: 3 years ago
You seem to be on the right track. As far as I have been able to discern from their literature, the Abbaka roof blower is appropriately conceived. (I don't have one, however, to confirm this.)

The silencer will be helpful.

I am unclear what you mean by the liner moving significantly more air. The roof blower fan curve and the hood aperture baffle system pressure loss vs. flow rate will be the first determinant of air moved. MUA pressure loss will be the second determinant. Do you by some chance have hood pressure loss vs. flow rate data?

Ah! I see Fantech list 750 CFM for this liner. But their liner is only 18 inches deep, of which about 5 inches is lamp bezel. Their flow rate limit is probably determined by noise and pressure loss.

The Abbaka liner is deeper, front-to-back, (22 inches overall) and the bezel area smaller. I would go with the Abbaka, given I'm using your wallet. Best would be at least 24 inches, front-to-back.

By the way, a 40 x 20 actual aperture (5.6 sq. ft.) requires 500 actual CFM to achieve a desirable 90 ft/min air velocity. Can I assume you aren't planning on running a char broiler that would require a higher flow rate?

500 CFM can be achieved with a HYEX-1.4 at 1.4 inches of pressure loss, and by the HYEX-1.0 at around 1-inch pressure loss. These values should significantly exceed the hood baffle pressure loss at that flow rate, but it would be good to get some data on that from Abbaka. In either case you do not want the part of this pressure loss to be MUA pressure loss. Plan on an MUA system. It likely can be passive if you have no combustion appliances. In other words, do not plan on achieving 500 CFM by overpowering your house leakage.

Please specify what combustion appliances you have and whether you want a fireplace to work when the hood system is running.
Jeff Bridges
Original Author
3 years ago
@kaseki, you are such an amazing resource, thank you!

I would go with the Abbaka, given I'm using your wallet. Nothing about a kitchen remodel is cheap is it?

Can I assume you aren't planning on running a char broiler that would require a higher flow rate? I am not going to run a char-broiler; but a secondary goal of the design is to move air our of the kitchen. I dont have a whole house fan, and it gets really hot in the kitchen. Plus I like expensive powerful toys. :-)

I do have some other combustion requirements that I hadn't even considered to be honest. I have 2 natural gas fireplace (rarely used), (2) 50G hot water tanks, and 2 furnaces in attic, 86% efficient 185k btu each if I m not mistaken

Regardless of the final flow due to pressure loss, there does't appear to be a higher performance system that I have found, unless you get into commercial/industrial.

And by passive do you mean non-powered MUA unit, or an open door/window? I am going to have to find a way to "sneak" that into the budget; wife just doesnt get it..
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kaseki
3 years ago
Passive meant blower-less.

Higher performance can mean one, some, or all of several characteristics, so I'm not willing to claim that your conceptualized system is the highest residential performance.

Another way to vent the kitchen besides using the hood is a ceiling register and suitable roof fan. One of those ceiling vents for cooktops (that in my opinion are pretty marginal) might do for venting oven cooking fumes if the oven/ovens are wall type. One might even join ducts to one larger blower on the roof, but careful tuning will be needed to get the cooktop component where it needs to be. In any case, MUA is needed to replace the air moved by all externally venting ducts.

With combustion appliances, the MUA is going to get complicated. If your attic is separately vented to the outside, then your furnaces won't notice any household interior pressure drops (I hope) and their existence can be ignored.

Do the hot water tanks have their intakes connected to the outside? Or are they in a room with its own MUA (passive perhaps) that otherwise is closed to air paths to the kitchen? If not, then the MUA safety requirement (independent of code requirements) is not to exceed the back-draft pressure of the appliances. See chart below kindly provided to us by another user here. The lower pressure drop values described are difficult to achieve with MUA systems without some complexity. Your life will be greatly simplified if the combustion appliances can be separately MUA'd. For the fireplaces, though, unless the type of built-in units with their own MUA, will be an issue.

Can I get some expert advice about sizing hood liner / fan

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kaseki

Jeff Bridges
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Can I get some expert advice about sizing hood liner / fan

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kaseki

Jeff BridgesOriginal Author

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Jeff Bridges
Original Author