Vent hood power?

Virgil · January 2009

I was hoping someone could tell me what CFM vent hood has worked for them using a large BGE. I can't seem to get any advice from BGE or any vent makers. I was thinking something pretty minimal would do (around 400 CFM), but the guy keeps trying to see me this 900 CFM unit. Its for an outdoor kitchen enclosed on 3 sides and screened on one side. Thanks,

Virgil

Little Steven · January 2009

Virgil,

900 cfm is a pretty strong unit. I am putting that size in for a 48" Range. I wouldn't think you would require that much for what you are doing.

Steve

Nature Boy · January 2009

Howdy Virgil
Our kitchen hood is 1200 CFM, and it does a nice job of sucking out whatever comes from our cooktop. Of course, that's inside. No idea how one would be sized for a room where air is coming in from 3 sides, but even 900 sounds kinda low if you want to move air.

Curious to see what the others say.
Cheers
Chris

Jeffersonian · January 2009

I'm not an HVAC guy, but I'd agree from what I know of the field. A 400CFM should work in all but the strongest winds.

Little Steven · January 2009

Chris,

1200 was the reccommended size for my old range. It had the grill and griddle combo. When it was damaged after the fire, I went with the French top so I downsized. We had already put a ton of air makeup in to compensate for the other stove.

Steve

Eggtucky · January 2009

It's about face velocity at the hood lip Virgil. Depends on the square foot opening dimension of the hood at the lip. There are easily available guidelines for this that tell you how to calculate total cfm based upon face velocity and square feet of hood. If the guy trying to sell you the 900 cfm unit is using a calculation that says velocity(fpm) x sq.ft=cfm, then he probably is calculating it correctly. if he's just saying he 'thinks' about 900 cfm, I'd go elsewhere for an opinion.

Firetruck · January 2009

A lot depends on the cost difference too. You are not doing yourself any good to undersize the system just to save a few bucks.

Fidel · January 2009

A good friend of mine is an HVAC designer. Let me know the square footage of the area and I can give you a good answer.

Nature Boy · January 2009

Another factor he might need is how many CFMs are coming out of the egg? When the egg is cranking at 550 doing pizzas, and burning up a pound of charcoal every 5 minutes, I wonder how many CFMs are coming out of the top of it?
Beers!
Chris

Fidel · January 2009

That was the first thing he asked me - how much smoke and CO pours out the top.

His honest opinion is that in an open sided outdoor area since pull is not an issue then a 400cfm fan right over the egg would be fine, but install a roof vent or 2 on the top of it just to be safe.

Coincidentally, he is in Virginia, so you know he can be trusted

stike · January 2009

sounds like it's essentially outside. tough to get a draft going with all that wide open free area.

bigger the better.

BGE won't help because (i'm assuming here) they probably don't want to be involved in what is an installation under cover.

Eggtucky · January 2009

Chris,
The amount of airflow coming out of the egg even with a 10 cfm Q fan is inconsequential to the air flow of the hood. This would be a class 2 (non-grease)hood similar to what is designed to exhaust heat and smoke over a pizza oven or in a kitchen and the volume of air flow required is more relative to linear length or sq footage of the hood. Don't mean to sound like a knowitall but I spent over 20 years doing HVAC engineering and design for industrial facilities in a previous life. Now if the exhaust from a BGE was anywhere near the intake volume of the hood, this could be an issue, but not the case with a BGE even with a 10 cfm fan.

Nature Boy · January 2009

Well, I am simply a graphic artist, and now a struggling small business owner, and very much right brained and non-technical....but seems like the output of the cooking device underneath the hood would be important. Reason we have a 1200 CFM is cuz we have 2 burners that are 22,000 BTUs, and an 18,000 and a 10,000 with a griddle in between. Somehow (and I have no idea why because I am a right brainer) these numbers affected what fan we used. And folks who had the same cooktop and lesser fans complained of smoke getting in the house when wokking something in a real hot wok.

Now you are talking about a 10 CFM guru fan, but to me that doesn't register, because that's just the input, and I have seen the wrath of the output of a 600 degree egg with both events wide open. Wonder if anyone has measured it?

And like Stike says, you have to create some kind of draft. You have air coming in on three sides. You don't sound like a knowitall. I'm just confused ;-)

Love to see how this thread develops!
Cheers
Chris

Fidel · January 2009

Interior fans are normally based on the size of the room in which they are installed. I don't think the BTU of your cooktop really factor in to it, but I could be wrong.

And in this instance air is only coming from one open side.

Nature Boy · January 2009

Hmm. Maybe a 200 CFM would suffice then?

Hell. I dunno. I'm just goin by feel (like everyone else in this thread?) and my feeling is that if I wuz cookin on an egg I'd want as much airflow as I could get. Especially on a screened porch. It would stink to put something in that didn't draw.

Or maybe I just miss posting on the forum and I am looking for a way to contribute....even though I know I am not qualified to answer this question!! hehe hehe.

Still fun. I miss hangin out here every day and posting up numbers like Fidel and Stike ;-)

Beers yall
Chris

Fidel · January 2009

Yea, rub it in...I have no life.

Nature Boy · January 2009

LOL!
Actually, you do have a life cuz you can do everything you need to do and still hang out here!

I'd like to feel I had a life when I was chalking up 20 or 30 posts per day. Hey, I DID have a life then!! Was just different. LOL.

Fidel · January 2009

It's easy, I just keep the laptop open while watching football....wireless internet makes it simple.

Eggtucky · January 2009

Chris, the explanation does get quite technical and goes way off topic of the original post. Plus I would probably bore you to sleep with the technical details and still not get you to understand, much the same way that you could probably not get me to understand why a certain graphic is higher quality or more marketable than another. Regarding your personal hood, I dont know without more tech details, but I suspect that the sizing of your fan was more dependent upon 'how' you would be using your burners and griddle (grease, no grease, etc), inside or outside, and the square footage of your two burners and griddle and the size hood that was required than it did with the BTU output of the burners and griddle. Also considered are things like whether or not the air being exhausted is conditioned or not, make up air (a whole other subject), and whether or not it has to be re-conditioned. Regarding your 'gut' feel on the roaring BGE, the air out cannot exceed the air in or the BGE besides being a great cooker, also creates air.

Secondly, the diameter of the opening of a Large BGE is 4", this equates to 0.087 sq ft of opening. At a discharge velocity of 1000 fpm this is still only 87cfm. I know it's deceiving, but I doubt that the discharge velocity in even a roaring BGE is 1000 fpm, that's about 1/5 of a mile in one minute. Sorry for the length of this reply but wanted to give you at least some understanding as you requested.

Nature Boy · January 2009

Ah yes. That does make sense. Especially the part about the opening on the egg only being 4 inches. The cooktop is much wider than that, which is why we need so many cubes. Makes extreme sense.

So...is there a correct answer for Virgil? How many cubes does he really need?

Been fun. Hope yall sleep well!
Happy 2009
Chris

Eggtucky · January 2009

Yes there is and since we've stolen his post the least I can do is offer to help him size his unit. So, Virgil, if my first reply did not answer your question, please email me with more details and I will gladly send you my opinion of what size your hood fan should be. Now, I am going to bed

stike · January 2009

if you want to help me "size my unit" you'll have to buy me a drink first.

(thank you, thank you all very much. we've had a wonderful time. if you happen to be in poughkeepsie for the convention, well, i'll be here through thursday. please, tip your waiter or waitress, and if you haven't yet, try the veal)

Eggtucky · January 2009

:laugh: :ohmy:

:blink:

:laugh:
in your case no need to..your wife already told me the size of your unit and it ain't a purty picture!

(thank you, thank you all very much. we've had a wonderful time. if you happen to be in poughkeepsie for the convention, well, i'll be here through thursday. please, tip your waiter or waitress, and if you haven't yet, try the veal)

Conundrum · January 2009

I hate to contribute to the "mine is bigger than yours war" but my hood is 1500 CFM and it sometimes falls behind but only briefly. My blower has 3 speeds with the fan mounted in the roof assembly. The set up allows me to run the unit at the middle fan speed for most cooks, the low speed for low-n-slo type stuff and WOT only for pizzas TRex and the like, which is nice from a noise persepctive as WOT is loud. My patio sounds about like yours - 3 sides of house and one open. One tip I've learned the hard way - pay attention to how the smoke vents, the prevailing winds, and the direction the open side of your porch faces. Every once in a while the wind will blow all of the smoke my hood evacuated right back into my porch which can be kind of unpleasant. If I had to replace mine I would go with roughly the same size.

Good Luck.
Reed

Vent hood power?

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