Double check my "hood math"

11 years ago

Do these specs look right to you? The reason I ask is that with all these specifics, I don't see a lot of choices and either I'm doing something wrong or these's not much demand in the market for this. The application is a 36" BlueStar range top on an exterior wall where the attic above has poor accessibility. My kitchen has an 8" ceiling.

Capture area: 48” x 27” (6” overhang each side, 3” front). 42" also acceptable
Style: Wall mount
Airflow: 1200 cfm or greater (Based on 112kBTU)
Blower: External (slightly less noise)
Exhaust Size: 10” (8" may work since the run is only a foot, but volumetrically speaking, I don't think it's ideal.)
Discharge: Horizontal (back side exhaust)
Material: Stainless steel
Filter Type: Baffle
Manufacturer Approved Height: 36” above cooking surface so 5'11" me and "mini" me teenage boy at 6'2" don't bang into it too much.

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Comments (4)

kaseki
11 years ago
OK, lets see how it works with a different "rule of thumb" using Galculator (http://galculator.sourceforge.net/), capable of operating in RPN like an HP-15C does and saving me from having to locate mine. Or you can ignore my plug for Galculator and follow using mental arithmetic because the numbers here are all simple.

A space of 48 by 27 inches is 9 square feet. Multiplying by 90 cfm/sq.ft yields a desired flow rate of 810 cfm. Duct losses are negligible, but baffle, transition, and MUA losses may be significant. Without more information (particularly a fan curve), we might stick with a nominal fudge-factor of 1.5 for working at some pressure drop on the fan curve. This yields a zero static pressure blower rating of 1215 cfm. 1200 is close enough.

If the blower input is designed for a 10-inch duct and the hood output is designed for a 10-inch duct, use a 10-inch duct, even if you have to frame out the studs to accommodate the location. Otherwise, the necessarily abrupt transitions needed to get down to 8 inches and back up to 10 inches within a foot will have some turbulence-caused pressure loss and noise you don't need.

kas
PRO
Trevor Lawson (Eurostoves Inc)
11 years ago
Are you getting a 6 burner or 4 Burner + ?

I would go.

42" wide x 27" deep x height 26"

1200 internal blower. (no benefit using a remote blower)

Mount 34" MAX from countertop.

Rear Vent.

10" Round Duct.

SS Baffles
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Robert Long
Original Author
11 years ago
The six burner version is the plan at the moment. Four burners is enough for 350 days a year. But we left "sane" behind in the rear view mirror a few kilometres ago.

I need to mock up the different heights with some cardboard boxes and see. Not saying you're wrong Trevor, I'm just saying I have to "experience" it because I cannot visualize less than 34" inches not blocking my view or banging my head.
PRO
Trevor Lawson (Eurostoves Inc)
11 years ago
We have a hood in the cooking school that 27" deep set at 32" above the countertop. To date fingers crossed not head banging has been reported. When you build your box try actually cooking with that in place.

Most people when I talk to them about hood depths focus on the hood and stand to close to the range, closer than they would if they were actually cooking. If I don't mention the depth of the hood until later they are surprised.

While a functional hood height is very important, enjoying the cooking experience is vital.