How much power is enough power? (In a range hood)

May 13, 2013 8:22 PM

We are finally getting a range hood for our oven! This is great! There are new building codes (2009 IRC M1503.4) that strictly govern how many CFMs a range hood can have without a make-up air unit. This is bad, frustrating, bad, confusing, bad and maddening. Everything I read gives me conflicting information. How much power does your average cook who likes to experiment but rarely uses all their burners at once really need in a range hood? (Lots of details inside).

So basically, a very long story boils down to the following bullet points:

-We are finally able to renovate the kitchen! I have long yearned for a shiny, wall-mounted chimney style range hood, and designed the floor plans around such a situation, without realizing how complicated the range hood situation was going to be.

-Every site I read assures me you need lots and lots of power in a range hood, the more the better (600 CFM or more)

-Some of the sites I read started to hint that something called make-up air was going to be required for such a powerful range hood if we didn't want to die horribly of carbon monoxide poisoning

-I found the 2009 International Residential Code M1503.4 that indicated that anything over 400 cfm was indeed going to require a makeup air unit.

-My local Building Inspector has confirmed they are enforcing this regulation in my city

-two separate a/c-heating experts have looked my house up and down and told me to forget about installing a make-up air unit. The house is almost 80 years old, and has no forced air heat or central air conditioning. The cost is prohibitive.

So, I am stuck. The maximum I can go up to in a range hood is 400 cfm. And, to be honest, I haven't seen many 400 cfm models that I really like. I have seen quite a few models (Zephyr, Faber) that offer a hood in the 700 cfm range, and the identical model at the 290 level. Of course, 290 is even lower.

So, how much of what I have been reading is, well, hype, a new fad, or aimed at people who will be doing much more fancy cooking then we might? We sometimes do have as many as four burners going at once -- but it is sort of rare, and more likely on holidays, or when schedules overlap. We would like to stop setting the smoke detectors off, however, and be able to do things like roast a chicken on high heat, or stir fry in a wok, without issues.

The oven is a GE Profile, 30" 5 burner gas range/convection oven with a second bottom/electric oven. According to a calculation run by the person at Best, they recommended 550 cfm.

Our fall back is a Best by Broan model that is not that high on my list of favorites, but has 400 cfm. My local appliance store guy was down on Best, however, not happy with the quality. He steered me towards Zephyr, and other brands (and also reiterated that I should go high for cfm).

Should I be spending this much time and effort worrying about this? Are there lots of people out there with 300 cfm models who live happy, contented lives, or will our kitchen be full of smoke and grease?

Also, if you have a range hood of this type that's right around the mark I am looking for (as close to 400 as possible!) please let me know what it is, any why you like it!

(As you might be able to tell from a lot of this question, I am feeling a lot of disappointment and gloom over what was supposed to be a high point of the kitchen for me, and which has just turned into a major headache instead. I had my beautiful Zephyr Savona 685 picked out and was very much looking forward to it.)

posted by instead of three wishes to Home & Garden (9 answers total)

We recently replaced all of our kitchen appliances and our hood is a Zephyr 1200S, which is an under-cabinet, 400 CFM model. I, too, would have liked a chimney-style hood but that would have required some renovations of the kitchen cabinets that I did not care to undertake. The fan is over a 30" GE glass cooktop with four burners. You can see what it looks like here.

FWIW, we cook almost exclusively Japanese and Chinese and I particularly get pretty intense with the wok. I have generally found that it does the job. We have been satisfied. I just turned it on to confirm that it runs at a decent volume. I don't have to shout to talk to people in the kitchen while cooking.
posted by Tanizaki at 8:46 PM on May 13, 2013

I have this 400CFM hood from Ikea (found in the as-is section). It gets the job done. The closer you mount it to the stove surface the better it will work; unlike commercial range hoods, it doesn't have a skirt around the perimeter to trap rising steam / smoke and funnel it into the hood, so you need to have a significant cross-wind over whatever you're cooking if you want it to extract all the steam/odors. Even with 400CFM it is still not enough to deep-fry / pan-fry indoors without having lingering smells, which I hate.*

That said, at least with 400CFM the whole make-up air situation is amply solved by just opening a window in the kitchen. This isn't exactly a difficult problem because the hood will work much better with a window in the room (or an adjacent room) slightly opened than with everything closed up tight.

I think the make-up air issue is a problem when you have kitchens in the interior of a building, or worse yet in a basement, where they can't easily just open a window to take in outside air. If you have a window you can open, I wouldn't (and didn't) worry about it too much.

Until I found the Ikea vent in the scratch-and-dent section I was looking at various commercial and commercial-esque vent hoods. My feeling was that the high-end "residential" stuff (JennAir, Wolf, Viking) is bullshit; they may look like real commercial vent hoods but they aren't, and you're just wasting your money. Unless you are going to spring for a no-shit commercial vent hood with a skirt and grease baffles (and hell why not get an Ansel system while you're at it) you should instead be buying based purely on CFMs and noise levels. The rest is just marketing.

Also the ductwork between the vent and the outside matters a lot to the actual CFMs delivered by the vent ... make sure that you use the recommended size of duct (in my case 8" IIRC, which the installer thought was absurdly large) and minimize the number of turns and especially 90-deg bends wherever possible.

* Unless the smell is bacon. Because ... bacon.
posted by Kadin2048 at 9:06 PM on May 13, 2013

I have seen quite a few models (Zephyr, Faber) that offer a hood in the 700 cfm range, and the identical model at the 290 level. Of course, 290 is even lower.

If the 290 model is truly identical, buy that one and then replace the motor with the 700 CFM motor after the inspector leaves.

And get a CO detector for your kitchen.
posted by jamjam at 9:09 PM on May 13, 2013

instead of three wishes: "two separate a/c-heating experts have looked my house up and down and told me to forget about installing a make-up air unit. The house is almost 80 years old, and has no forced air heat or central air conditioning. The cost is prohibitive"

This part doesn't make any sense unless there is some special requirement encapsulated in the term make-up air in your region that doesn't apply here. At it's most basic make up air is just another fan the same size as the exhausting fan that takes outside air and blows it into the conditioned space to prevent depressurization and maintain the efficiency of the the exhaust. In commercial spaces this air is often heated and or cooled to maintain internal temperature but commercial kitchens have massively higher air handling requirements than even the 1000 cfm fan you are coveting.

See for example the unit outlined in this PDF which is nothing more than a fan, some ducting and a pressure switch in the exhaust duct. These systems (PDF1, PDF2) can provide heat for self contained systems. Those units aren't as cheap as the fan only units but they shouldn't be cost prohibitive to install considering your choice of appliances. With a 600 cfm exhaust fan you would only need a a 200 cfm of make-air to get you below the regulation threshold. Even if you need to heat or cool your MUA that's not a lot of volume to handle. Ideally you'd want to dump that air near the appliance so it could provide some of the MUA heating.

Finally 1000 CFM for the stove you outlined would be crazy overkill; the 550CFM the sales guy calculated sounds more reasonable.

PS: barring substantial efforts to reduce the permeability of your building envelope it's highly likely that your 80 year old house doesn't require make-up air in the first place; compliance is a regulatory issue in this case not a safety or efficiency issue.
posted by Mitheral at 9:36 PM on May 13, 2013 [1 favorite]

In my last house I installed a 600CFM Zephyr model, and I would not do it again. The thing was really loud at top speed -- enough to inhibit conversation and be wearing to work around. I have used quiet, high-volume range hoods at other people's houses, but they were not compact little Zephyr units; those hoods were much bigger, heavier and more expensive than anything Zephyr made at the time (I haven't checked their catalog recently). Also, 600 CFM was not some magical threshold that allowed me to make as much smoke as I wanted; I still managed to infuse the whole house with the smell of smouldering beef fat a couple of times. In those extreme situations, a nearby window fan facing outwards did a better job than the range hood could.

I've since moved, and now have a thoroughly uncool LG OTR microwave with a 400 CFM blower, vented out through an exterior wall. It hasn't cramped my cooking style noticeably.

I would suggest you keep the ductwork as straight, smooth and short as possible. If the kitchen position / layout is such that the duct run is at all long or convoluted, you may want to go for a bigger blower just to to offset the static pressure. Far better, though, to arrange things such that a long, convoluted path to the outside is unnecessary. Also, I think it's a lot more pleasant, noise-wise, to use a high-volume hood on low speed than it is to use a lower-volume hood at top speed, even if the volume of air being moved is the same.
posted by jon1270 at 4:09 AM on May 14, 2013 [1 favorite]

Also, a GE Profile, 30" 5 burner gas range/convection oven with a second bottom/electric oven is exactly what we had in our last house, and similar to what we have now.
posted by jon1270 at 4:27 AM on May 14, 2013

IAAL, but not your lawyer. Laws is laws. Range hoods need to be able to protect against fires when all the burners are on, even if you promise you won't do that. There's zero possibility you'll get a building permit based on promises not to use all the burners.

Instead, consider adding a single super-burner or grill that can squeeze in under the powered ventilation rules. Your local contractors will be able to give advice and suggest workarounds.

Cheating on ventilation endangers you, your family and your neighbors. It's not just about carbon monoxide. It's about FIRE. Oh, and by the way, if you have a fire (or CO poisoning), the first thing the fire insurance company's inspectors will look for is whether you violated the fire code. If so, they'll cancel your insurance retroactively.
posted by KRS at 6:35 AM on May 14, 2013 [1 favorite]

Response by poster: A few more data points:

-the new floor plan is set, the cabinets already ordered. So, no under cabinet model or microwave can be substituted.

-The good news is that it will be right up against an exterior wall, and venting straight out, so we will gain some ground there.

-I know that with a house this age, there's a lot of leakage, and opening the window would do the job -- but unfortunately, this is not okay with the inspectors. And perhaps because of my location (cold cold winters, lots of snow, hot humid summers) Neither A/C-heating specialist was willing to go forward with a plan that just dumps untreated air back into the house. They wanted heating/cooling involvement, and for the air to be pushed up from basement to first floor.

jon1270: Thanks for the tip about Zephyr and noise. They have a new line with noise reduction that I may focus on instead, knowing that.

KRS: I know you probably meant to help with your response, but my entire question was devoted to the fact that I intend to follow the regulations on this issue, and just spent way too much of my life researching what is allowed and safe. And why on earth would I add another burner to the mix, when it would only increase the need for a more powerful range hood?
posted by instead of three wishes at 7:21 AM on May 14, 2013

I have just installed this from IKEA over my five gas burner stove. It is my friend. When cooking is very intense, I open the window too, but that is because of the heat.
posted by mumimor at 11:34 AM on May 14, 2013