Hoods, cfm's, and do I really need as much as they say?

16 years ago

Hi all,

I'm hood shopping (have read all the relevant hood posts here on the forum). TheHusband, who greatly dislikes spending money, is less than thrilled about the price of these hoods. I need a retro style for my kitchen, which, as far as I can tell, leaves me with the Vent-a-hood excalibur, and a Modern-aire one. The latter is about twice the price of the former! And, of course, it is the one I really want.

I *might* be able to swing it, but only with the 400cfm blower. "Technically," I should have a 600cfm for my range. (I have a vintage stove with 4 12.000-13,000 btu burners, and a 9,000 (I think) griddle. TheHusband insists that the technical specifications are hogwash, and since I'm never running all the burners and griddle at full capacity, 400 is more than enough. Money wise, 400 is probably my only option. But I don't want to spend so much money, and then not have sufficient cfm's. That would be a costly mistake!

So, who's got 400 cfm's? And do you wish you had more?

Thank you!!

Francy

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Comments (9)

Fori
16 years ago
Have you been using this stove? And what ventilation do you have now? Do you do much fat frying? DO you do much at full power? If things get bad, can't you just bring in a box fan and open a window? :)

Most of those old ranges aren't vented at all (and have the sticky kitchens to prove it!). Even if 400 isn't enough (I suspect it would be for most meals though), it's still not entirely wasted. It'll still catch a lot, maybe not as much as a 600, but most.

On the other hand, you don't have cabinets on the sides to help funnel steam up...what size hood are you considering?
weissman
16 years ago
I have 600 CFM's and rarely use it on high and I have 4 16K burners and 1 17.5K burners. On the other hand, it's nice to have the high speed when I'm doing something with a lot of smoke. I do agree with your husband that the math is overrated - you'll never have all your burners running on high at once. Most likely 400 CFMs will more than meet your needs. You are venting outside, right? Just out of curiousity, how much more expensive is the 600 CFM one than the 400 CFM one.
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Start with the uprising effluent velocity of around 3 ft/s or 180 ft/min, multiply by the hood aperture area in square feet. This is the air flow (cfm) required to capture and contain the cooking plume that is intercepted by the hood if the surface the rising plume meets is relatively flat and horizontal. With less velocity, some effluent may "reflect" (curl) out of the hood. For pyramidal hoods, usually sold with baffles, the interior reflection angle is predominantly upward, and this allows the cfm to be less because some of the effluent momentum is still carried upward after the first bounce. One might get away with a factor of 0.5 on the product of aperture and plume speed. For example, a 6 square foot baffled hood of the pyramidal style (e.g., commercial, Independent, or ModernAire baffled hoods), would require around 540 cfm (actual). Please consider that due to various duct pressure losses, hood pressure losses, and house negative pressure, the actual flow rate that a particular blower can move will be significantly less than its rated (at zero static pressure) flow rate. So, a four square foot hood would require 2/3 of the above calculated value, or 360 cfm. But to make up for the losses, the blower should be rated perhaps as much as 1.5 times larger to actually move 360 cfm. C.f. Blue Star's choice of words: "... move a minimum of 300 cfm." Please consider all these values nominal, and dependent not only on many factors not accounted for here and rarely specified so that they can be accounted for, but also on user tolerance for odor, type of cooking, etc. kas
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Sorry ribs1, you're caught in a situation many of us don't face and I surely empathize with the expense of conditioned Make Up Air (MUA) due to code. I read the OP asking about Blue Star BTU and venting CFM's. MUA is increasingly considered and discussed when re-doing or building a kitchen, and should be discussed pre-purchase of a pro-range. MUA has been an active topic of interest here on GW as well as on greenbuildingsdesign.com in "Makeup Air for Range Hoods" (linked below) and on many HVAC forums. Good reading and sources for solutions for industrial conditioned MUA (which perhaps will help you somehow too ribs) are also found on http://www.greenheck.com. MUA, passive or active, is available without excessive expense for most of us as we are not restricted, as yet, by specific code requirements. I'm firmly in the camp of matching one's cooktop/range purchase to one's budget for proper ventilation and MUA and more to avoid any risk of acute illness/death due to carbon monoxide poisoning from lack of replacement air. Here is a link that might be useful: Makeup Air for Range Hoods
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The problem Beatrix is not leaving people breathless. The issue is in tight construction the air you are venting outside with the kitchen vent has to come from somewhere and since it can't seep in around loose doors and windows it finds different sources by sucking air down chimneys used for other appliances like furnaces and hot water heaters or for your fireplace. If any of these appliances is in use, it therefore draws the combustion products like CO and CO2 back into the house and could theoretically cause asphyxiation. If your fireplace backdrafts you will probably notice the smoke and burning wood smell but CO and CO2 are odorless and could easily go unnoticed. With new construction makeup air is important. While an open window works, people will forget sometimes to open one, so code is beginning to prescribe some automatic source. The reason it can cost $5000 is because that quote probably includes a furnace to warm the outside air to room temperature in the winter.
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OK, youall have succeeded in drawing me into another argument. Let's start with the purpose of the overhead vent. The vent is intended to capture and contain effluent contained in the rising and expanding cooking plumes. It has an overlap capture requirement that depends on height, and a flow rate containment requirement that derives from plume velocities and secondary factors. It is not for capture or blockage of grease splatter, as that could require enormous air velocities to achieve. Down-draft "venting" and pop-up side-draft "venting" cannot achieve the needed capture and containment provided by an overhead hood of proper specification for these reasons: Air flow velocity drops rapidly as a function of the smallest dimension of a slot air intake (see the 2003 ASHRAE HANDBOOK, HVAC Applications, Fig. 6). The air velocity in all cases is too low to significantly change hot cooking plume momenta except those plume portions close to the pop-up, so the overhead hood depends on the natural rise of the plumes. Deviation of the upward momentum to the side, or by 180 degrees to head downward, can only work if the plume has low momentum, as in steam from boiling water. Hot oil/grease/moisture plumes from wok cooking and searing will be poorly deviated sideways or in reverse. Fume hoods can have horizontal hood configurations, but the top and sides are blocked from allowing fumes to leak out. The turbulence issue is complicated. Up-rising plumes can be disturbed by side drafts, poor insertion of make-up air into the kitchen, and cook motion. Side-drafts will be pulling air across pan and pot clutter, so some added turbulence is possible, but I don't think it will be a significant addition except close to the pop-up due to the velocity fall-off introduced above. On the other hand, a pop-up can block splatter trajectories from the burner up the the angle between pan and the top of the pop-up and as far as the pop-up sides shadow the area beyond. For this function, no air flow is needed and much of the pop-up system hardware can be dispensed with. If a blank face is used (no vent holes/slots), cleaning may be greatly simplified. Underfloor ducting, blower, external cap can all be deleted. Some cabinet space for the elevation mechanism has to be sacrificed. While a pop-up splatter blocker is a good idea if the degree of blockage is deemed sufficient for the expense, the subject raises the question of why children are sitting in range of hot grease splatter. At a minimum they would need eye protection. There are requirements (that I don't have at hand) for desirable rises and/or runs of seating countertops connected to cooking surfaces. I recommend proper desks in quiet areas for studying. The student should be fully absorbed into the material to be studied without distraction (or at least as little distraction as a post pubertal youth can manage).
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bayareafrancy
Original Author
16 years ago
Currently I have no ventilation. I don't even have a stove pipe, so we sometimes have a lovely "gas" smell in the kitchen. I do little frying/sauteeing b/c the wall behind the stove gets so gross! So I'm looking forward to doing more! But only on one burner at a time. And the griddle is strictly for pancakes (so no fat frying).

The stove is 39", so I'll need the 42" hood. Eventually I'll have a cabinet unit on one side only. I *think* the 600 would be between $200-400 more (I was quoted 1471 for 400cfm at 18" high vs 1855 for 600cfm and 30" high. So those prices encompass 2 different heights as well as blowers.

And rats: just realized those prices probably don't include those nifty cute bands that give the hood its retro look. Oh shoot!!!!

Why does everything stylish have to be soooooooo expensive!!!!!???????TheHusband and I are not $2,000-hood-people. Rats, rats, rats!!!!!!! The Modern Aire is just much more beautiful than the Vent-a-hood.

Francy
igloochic
16 years ago
You could buy a vent a hood insert and then do something custom on the outside (which we're doing). You can keep your prices down that way (sometimes) :) And keep within the style of your home.

We have a 600cfm Vent a Hood and significantly more power than you do for your stove. Vent a Hood cfm's can be smaller than the recommended cfm's because if their technology (so 600=900 for vent a hood). Don't ask me why, read the literature LOL Cuz I can't explain it :)

One thing you could consider is to bring your hood out from the wall a bit as well. You can compensate for lack of power by higher coverage. If the hood dosen't have to suck in so far from the front burners it won't need to be as powerful.

We brought the VAH insert out to 27" which completely covers our range. Even with that added expense (we had the entire insert rebuilt but this isn't necessary...I just wanted to) and a 58" hood, we still aren't at $2000 for the hood. (but we're darned close!)
bayareafrancy
Original Author
16 years ago
Ah--depth! I never even thought about that! The vent-a-hood is 24" deep. To cover my front burners, I need about 26". I don't know what the M-A depth is.... But if it is deeper than the v-a-h, that would make a difference!

I haven't even looked into custom hoods, b/c I assumed it would be a lot more expensive. I could check it out. Though I dearly love the design of the M-A: it's the one in klb's beautiful kitchen.

Thanks again!

Francy
housekeeping
16 years ago
Ventahood makes a 27" deep hood in some styles and when I was pricing it on line a while ago it wasn't more costly than a 24"

I think I've got my head wrapped around the simple explanation for why VAH cfms are "equivalent" to higher cfms in other fans: it has to do with the fact that the exhaust air path is less obstructed because of what my DH calls the "fat slinging design" vs a design that has to suck the air through a metal filter to extract the grease.

I'm going to go with a 27" deep one because my stove is unusually deep front to back and because I'm mounting the hood more than 30" above the range surface. This is just a temp set-up so we will be able to judge if the height is OK before moving it to its permanent place in another room in a year or so.

Molly
orangedaisy52
16 years ago
I have 400 cfm with four burners, largest is 15,000 btu. It's at an 18 inch height and seems just right (except that height is way too low...always bumping into the hood.

I got a 400 CFM external blower from Fantech for about 300...I don't think 600 is that much more. I also got the silencer (very important) for about 125 and I think my entire installation including labor and all new 8 inch ducting(going into my previously existing hood) was about 750. That would leave a lot of money left over for a retro hood of some sort. Fantech also makes liners to put into whatever hood you have. hmmm maybe you could buy an old hood on ebay or something (like the vintage of your stove and spruce it up? Here's the link

Hope it helps

Here is a link that might be useful: Fantech fans
kailleanm
16 years ago
We are also using the Fantech system (400 CFM). However our kitchen is very small and has three opening windows, so we are just planning to use the grille in the ceiling with no hood.

If your DH can install it himself, you could save even more money for a fan. My DH did ours yesterday and didn't have any problem, though he is a tradesman (carpenter).
sleepydrj
16 years ago
We were also looking for a retro look. We used the venta hood DAH30/DA30 Flairline hood in white enamel (white river?) which really attempts to hide in our kitchen. The scooped-in shape gives it a retro appeal. It is very close to an arch shaped doorway to our kitchen nook, and so we really wanted to de-emphasize our hood.

Never had the chance to fall in love with the excalibur, hadn't ever seen it! Still, I probably would have ended up with this one since we really want it to blend in.

The ventahood technology is supposed to give more pull per cfm, so you can order a "lower" cfm hood. Mine is definitely sufficient for my 36"wolf. I haven't used it with my infra-red grill yet though!! luckily there are windows all around if it's not enough!!

Hoods, cfm's, and do I really need as much as they say?

Comments (9)

Fori

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Hoods, cfm's, and do I *really* need as much as they say?

Comments (9)

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Hoods, cfm's, and do I really need as much as they say?

bayareafrancy
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