External blower for hood in Garage??

15 years ago

For all of you experts out there.....I'm trying (desperately, I must add) to finalize my cooktop/hood choices and have narrowed it down to the Bluestar 36" 6-burner slide-in or the 48" 6-burner slide in with grill. The hood would be a Best by Broan IS4290 with 1000Cfm internal blower, or the ISER222 with internal (1000) or external (1500cfm) blower. This is an island application and there is a bath/hallway above the kitchen. The ducting would go up about 3 feet, make a 90 degree turn, and then out the side. GC wants to have it exhaust into the garage. Not having dealt with a hood before, is this reasonable? I assume the grease would be trapped, and the only thing vented would be hot air and "aromatic" vapors (which I'm not too concerned about. The garage has a very high ceiling, to vent out above would result in another 90degree bend and another 6' up. The horizontal run from the hood to garage is about 10'. (this is what we get for designing a house with a kitchen dead-center!)

Hopefully someone can shed some light on this....I thought it was odd, but if it'll work, I'll go for it.

Also, can anyone chime in as to just how loud a 1000 cfm internal Broan blower is?

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Comments (10)

racerdinah
Original Author
15 years ago
Actually I need to clarify something in my question....no matter which type of blower I choose (int/ext), GC wants to vent into garage.
racerdinah
Original Author
15 years ago
Ok, never mind about the venting INTO the garage. I called the GC *again* and asked him to clarify what he meant....no, he meant the duct would run THROUGH the garage and out the side, which is not what he said the last time I asked.

If I could delete that part of my questions I would. Jeez....

My question about the noise level of the Broan hood still stands...
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In my view, losing only 300 cfm given the duct pressure loss, the hood transition losses, and filter losses, is pretty good for a fan curve. However, I would suggest using a larger 1500 cfm fan to improve chances of successfully capturing and containing the effluent that is possible from such a large and powerful cooktop. Given the hood size that is needed, a large flow rate is needed to keep the air velocity high enough at the hood aperture. It is essential that the hood overlap the cooking surfaces by enough to capture the rising expanding effluent. Assume from each cooking surface an expansion half angle of 22.5 degrees, and determine for the intended hood height whether the expanding cone stays within the hood aperture. Don't ignore that when Broan or others assert a flow rate, they are assuming that the cooking area pressure equals the outside pressure. This would require an outdoor kitchen or near perfect make-up air system. Any house negative pressure will cause the maximum flow rate to drop per the relevant fan curve, another reason for increasing the fan capability. Broan publishes their fan curves so the effects of pressure loss can be clearly quantified. kas
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I may have failed to notice catinthehat's response of April17, 2018 because I don't see a response from me. Thanks for the link. Ria Raj: The fan curves by duct length can be converted, but either way don't tell the critical part of the story -- what is the pressure loss vs. flow rate of the hood with baffles in place? This pressure loss may be expected to dominate duct loss when using 10-inch ducts at the 1400 CFM blower's full power, even a 100-feet's worth. And that assumes no MUA pressure loss, which will certainly exist, even with a sophisticated active MUA blower system. I still recommend assuming a 2/3 of rated actual flow rate when all of the variables are not known, and using that value divided by the hood entry aperture area to achieve roughly 90 CFM/sq. ft. My asserted hood rule is: Overlap the cooking plumes to achieve good capture, get the velocity in the baffle gaps up to roughly the highest plume velocity, ca. 180 ft/min. (With induction one might squeak by with a bit less due to lack of a gas flame aiding the upward velocity of the plume.)
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Differential means the difference between the outside temperature and the temperature you want the MUA to be (warmer or colder than outside). CFM means actual hood CFM, and the actual hood CFM will never exceed that provided by all the sources of MUA CFM available at the kitchen. If the differential pressure is zero, then one has perfect MUA (pressure balance) and the hood will only be "gagged" by its own baffles, transitions, and ducting. The achieved indoor-outdoor differential pressure won't generally be zero, but it can be kept modest relative to changes on the fan curve. Aim for 90 hood CFM per square foot of hood intake aperture. This should provide complete containment for most cooking for captured plumes using residential hoods with baffles. (Plumes are initially captured if the hood aperture overlaps them.) So, for a desired/required 800 CFM, say, one finds 800 on the abscissa and goes up to a differential temperature curve representative of an outdoor and indoor temperature difference, and thence left to the ordinate where the BTU/hr needed is listed, based on the specific heat of air and the mass of air being moved at that CFM. BTU/hr has a counterpart watts value for electric heating, and also a tons of air conditioning value if one intends to cool. Conversion factors may be found by use of an Internet search engine.
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+1 to what @kaseki said. Is it going straight out the back of the hood or up in to the ceiling and then out? The latter would be much quieter than the former and both s/b quieter than having it in the hood itself. Make sure to isolate the duct and blower from the house structure to avoid vibrations being xmitted through. A larger hood and in particular greater containment volume will allow you to use lower CFM's (which generate noise) for the same or better effluent removal.
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heimert
15 years ago
Yeah, it would be crazy to vent *into* your garage, since you'd be cleaning grease off your vehicles daily. Venting *through* a garage is fine, unless you had planned the area for storage (You might have him put some 2x4s around the duct to protect it from dents from surfboards/skis/bikes/ladders/whatever.

As for the plan, it seems quite fine. I imagine it would be this way, but have him put the fan in the garage, not under the hallway--the reason for a separate blower is to get the noise elsewhere.
amirm
15 years ago
A note on internal vs external blower. I have been told that to get an external blower serviced is a pain. Appliance repair people may claim their insuarance doesn't cover climbing the roof or even on a side-mounted blower.

So if you are on the edge, go with internal blower....
racerdinah
Original Author
15 years ago
amirm - many thanks for the head's up. The issue is the cfm....the internal blowers just aren't strong enough.
alexamd
15 years ago
I have an inline Prestige blower with the duct work going through my garage and out the side. I have a 48" Bluestar with grill. All seems to work fine. The fan on high is a little loud, but on low is tolerable. I don't run it as often as I should. I guess that it is all those years of not having an exhaust fan.
racerdinah
Original Author
15 years ago
alexamd: Thanks for the info. May I ask how often you use your indoor grill, and what the weather is like in the winter? We live in upstate NY and having to run outside to grill with 2' of snow on the deck isn't so appealing. And I love grilled food (veggies, shrimp, chicken, etc). AND the option of using the griddle pan over it is inticing. Having said all that, I just plugged all the #s into a spreadsheet, and the bigger hood + additional cost of the grill unit puts it $2000 over the "plain old" 36" 6-burner with slightly smaller hood......trying to decide if its worth it. I've lived without it all these years and can use a grill pan if I have to.....but...you know how it is when tempted by all these nifty appliances!
alexamd
15 years ago
Originally, I was going to get the 36", but switched to the 48" to get an extra oven and the grill. We live outside of Boston and we used the grill quite a bit over the winter, but now that the nice weather is here we use the outside grill. I won't fool you, the outside grill does a better more consistent job, but the inside grill works well enough for a substitute in the bad weather. Once the range was installed, I didn't use my outside grill until the weather got nice again.
User
15 years ago
Be sure that your contractor is planning to create a soffit in the garage for your ductwork to run through and not planning on leaving it bare. The wall between the garage and house must not have any penetrations into the home for fire code reasons. Therefore, any ductwork running through a garage needs to be covered with drywall from the kitchen through where it exits the home.
racerdinah
Original Author
15 years ago
Live_wire_oak...thanks for the advice. I'll make sure to double-check.

External blower for hood in Garage??

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External blower for hood in Garage??

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