With that short a run I'd tend to agree you lose much of the benefit of an external blower. I think there would still be some benefit, as some of the motor noise emanating from the housing itself will be kept outside, so it's only the motor noise and fan noise that will travel through the duct that you'll hear, but certainly it won't give you the full benefit of a remote installation, especially when a silencer is used.

If you did lengthen the run to move the wall-mounted external blower further from the stove you might increase the benefits. Any increased loss of airflow should be easily compensated for by using an adequately sized blower.

I agree with your instinct, which is to stay with a higher-rated blower. As the cliche goes, you can always turn a larger blower down, but you can never crank a smaller one up above its maximum capacity for those infrequent occasions where you need maximum exhausting. The key in my mind is to use an infinitely variable speed control which allows you to run the fan at extremely low speeds when you don't need much airflow, thus keeping the noise levels way down.

I'm hoping that someone with a similar installation (a very short run of duct that goes right out the wall) will jump in as this is very different than my two installations and I suspect there are issues specific to that kind of installation I'm missing.

Clinresga: Thanks. Your posts have been a real master class for me, along with your links to other useful posts. I covet your current ventilation system (main house, not lake house). Alas, attic silencers are but a dream for me! I'm hoping someone else in my short duct boat will weigh in here, particularly re. pros and cons of running additional duct along outside of house...

Anyone?

the overheard appliance salesman was correct, and what he said concurs with what all contributors here have said too.

You will have seen in all the other threads that some subjects are important: the position of the hood, its canopy shape and collecting capacity, your cooking type, etc. The subjects you raise and questions you ask, viva99, are fine-grained detail. Silencers, extra runs, remote blowers, etc. I'll answer your subjects and your questions.

If where you live there are stores that have installed working range hood fans (e.g. with ducting going nowhere, just pushing air out the top of the appliance), then go listen to at least one of the several models on the market that have ".... an infinitely variable speed control which allows you to run the fan at extremely low speeds when you don't need much airflow, thus keeping the noise levels way down. ..." You will hear minimal noise and it may be fine for your ears. I believe it will be. With a Variable Speed Controller you will enjoy it, and enjoy being able to adjust at will.

Since your ducting is short, IMHO this is all you'll need. Yes the blower is in the front end of the duct run, internal to the hood (so I've learned it's called an internal blower). This is what 99% of all hood fans are and they work for millions of people. When they work well, they make less noise than your house plants do when their leaves move under a gentle breeze.

The other two blower options are inline and external. You don't need this. Here is why. Your duct is short. All blowers get weaker when they have to push air against a head of static pressure. Even when the air current gets flowing, the blowers still strain, struggle, hum, chop the air current up into a more turbulent flow, and so they make more noises in various and sundry ways. You don't have that happening when the duct is a short length.

Referring to the charts you will see in all the spec sheets (on manufacturers' web sites), the curves showing the blower's loss of its ability to blow air against a resistance (air pressure), a significant load is placed on the blower when there is a long duct run (and Elbows!). So, what the appliance salesman said was correct, and it concurs with what all contributors here have said too. A short duct with no elbows, means you get a full clean almost-silent 300CFM or 400CFM when you buy a product rated for 300 CFM or 400 CFM, and on top of it all, you get that performance without irritating noise due to the blower pushing against resistance and performing less. If you want to have double or triple that CFM, you certainly can and it will work too, very well ! I'm all for having more.

I'll guess that you can find a Variable Speed control in a Broan or Best by Broan product, installed in a store. I'd be glad to hear if you can find others.

((p.s. I have ordered a Pass & Seymour variable speed control for my inline blower installation.)) It is always good when you can get all the parts in one complete product, so I won't recommend doing what I'm doing. Only a motor designed for variable speed operation can take a speed controller.

HTH
-david

HUGE help, David. Yes, I had a vague sense (no doubt from here) that short ducts were in fact more efficient, but somehow missed the part about them being quieter, too. Don't have any house plants, but your analogy is music to my ears! Also, that's great advice about listening to various range hood fans in person. No such stores near me, but I'm willing to drive many a country mile to get the firsthand lowdown on noise. Thanks so much for all the time, care and insight you put into responding.

I tend to have a different take than David on this. It seems sensible to argue that short duct makes lower resistance meaning blower doesn't work as hard leading to quiet operation. I just don't think it works that way.

From what I've seen and read, it's my belief that the major source of noise with an internal blower is from 1) the turbulent airflow generated by the fan spinning at high speed 2) the motor itself (i.e. the humming or an electric motor) and 3) turbulence from air as it flows across baffles or filters and then in particular where the air exits the hood and enters the ducting. I don't believe running an internal blower into a low or moderate static load will change the noise level much: I think that's intrinsic to the basic operation of the fan. Short duct length has no effect on number 2 or number 3.

This is speculation that can't be proven without either experimentation or the involvement of a higher power (kas?).

And I don't want to be pessimistic, but I am hard pressed to believe any internal blower, running at any kind of decent velocity, is going to be quieter than the rustling of house plants in a gentle breeze. That strikes me as the fantasy of an ad agency selling hoods. Heck, even my inline blower, located 25 feet from the hood, with a silencer in between, is louder than that, just from air flowing over the baffles.

Noise is friction and friction creates noise. The friction will come from the motor, the fan(s) the hood and ductwork. The shape of the hood will cause differences in frictional flow ... turbulence ... as will shapes of the ductwork, arrangement of baffles. the more ductwork exposed the more noise is transferred to the room. So, in the end...don't overthink the plumbing or you will stop up the drain. Have you checked the sone specs on the various hoods...they arent the most trustworthy but they help.

Clinresga and peterf:: thanks for the alternate perspectives. One thing that seems clear is I should try to get as many settings as possible and make sure I can turn the fan down LOW, LOW, LOW. As for the $64,000 question of what makes vent hoods noisy, I'm still pretty fuzzy. I wish somebody would put me out of my misery and test all the variables INDIVIDUALLY. Until then people like me will rely on the benevolent expertise of people like you...

So. Leaving aside the question of whether a short straight duct is quieter in and of itself than a longer/curvier one, do you agree that the former would allow the fan to do its job at a lower setting than the latter? And if so, does a lower fan setting correspond to a substantially lower noise level? Or does X amount of sucking create X amount of noise, no matter what setting was used to get there? Does that make any sense? Anyone?

Sorry if I'm being redundant or extra thick. Just trying to get a grip on this... I know that if I spend all this time researching, then plunk down 7 grand on a powerful range and kick-ass vent hood, only to pine for my anemic whirlpool-with-no-vent-whatsoever, well, it'll be... ironic.

Viva - stretch out a flexible straw and blow through it at a steady rate. Now bend the straw to create an "offset", i.e. two 45 deg bends but the end still facing away from you. It got louder right?

Now straighten the straw again and blow through it moderately hard, and while blowing take some scissors and cut the straw an inch or so from your mouth. (Watch your nose!) It got easier to blow, right?

You're right, it's hard to find objective data. People can make references to leaves blowing, quiet conversation, etc. that we can all relate to, but CFM comparisons seem to be out of whack. On clinresga's thread (linked below) on 10/8/08 parrym notes says that at his Kobe's lowest setting of 380 CFM he can barely hear the vent, and notes that this speed is sufficient to capture light whisps of steam. I'll offer my experience with a 360 CFM (max) Broan that my mom has: At full speed it's pretty loud, but even with several pots of water boiling simultaneously I've never had need to turn it much above halfway. What gives? I don't know.

I would suggest that you look for a brand that advertises its quietness and has infinite variable control, more max CFM than you probably need, and beyond that stop stressing.

Here is a link that might be useful: the other thread.

Couldn't have said it better.

Viv99, you want speed control. You do not want to ".... try to get as many settings as possible...." because "Settings" means only 3 or 4, and you will not be satisfied with the result. There are NO motors with large numbers of settings, therefore go for a motor with a Speed Control. This is your only option. Final answer.

The criterion is noise when on Low. Most people don't care much if it makes noise at its highest setting, but this could be one of your other less-important criteria.

Yes, get a big one and leave it on Low almost all the time. Get one whose normal "Low" noise is agreeable to you.

The disadvantage of having only 3 or 4 settings is that you have almost no choices if you want to keep noise down. The top two settings usually make a noticeably larger noise than the first one (or two), and this noise Appears Large because of the discontinuity; it's subjective. When you can "dial it up or down" to suit your instantaneous whim, you are generally satisfied with your chosen setting on the slider.

Perhaps in Germany a state agency will "test all the variables". Here, government only gets involved with safety, not comfort or convenience. Noise is just a necessary by product of moving air. It might take thousands of years before we establish reference benchmark noise(s) and a grading system that is fine-grained enough to be useful in the range of "nearly-as-quiet-as...".

HTH
-david

My perspective is that a higher-rated cfm blower will be larger, and hence when run on low will generate less turbulence off of the fan blades than a smaller fan running on maximum to achieve the same cfm. (Viz., Casablanca-style ceiling fans are very quiet, but move a lot of air.) This will, of course, depend greatly on the design choices made by the manufacturer. Also, optimal designs for pushing air into static pressure differences will be different than optimal designs for best pulling air through static pressure differences.

A sufficiently noise-adverse person could consider how to duct outside a wall, then pass the air through an external silencer to a blower. This seems to me to be a "project" that would involve several considerations besides cost, such as external aesthetics, weather protection, etc., so I'm not recommending it, particularly when the required cfm is modest relative to the capabilities of higher cfm-capable push or pull blowers.

I think the over-kill solution run on low is the best choice. Further, if you have a noisy party and want to wok cook or engage in similar massive grease generation, you can always crank the blower up without it being heard over the din.

kas

I think I've finally got it! I'm looking for a somewhat oversized hood with an internal blower that offers more CFM's than I'll usually need + infinitely variable speed control in a unit/brand that specifically claims to be quieter than most and can back up the claim in a showroom comparison (if possible). The rain in spain falls mainly on the plain!

Seriously, I'm much obliged to you all for finally clearing the fog in my brain -- sucking it away through some short, straight duct, as it were.

David -- thanks for giving me the correct term, "speed control." When I said "as many settings as possible" I was attempting to say "infinite settings" without sounding greedy or unrealistic. But infinite it is!

Ya think -- Bravo! That's an ingenious experiment. Just wait til I get my hands on a flexible straw! Until then, I'm going to take your word for it, and trust that my short duct, no curve situation has some advantages after all. And stop stressing. Also, thanks for the link, but that's the thread that got me thinking about this stuff in the first place... Worth reading again, though. Fascinating.

Kaseki -- It had definitely occurred to me that extending the duct along the outside wall for the sake of a silencer and more remote blower would entail major aesthetic and financial sacrifices (housing it, weatherproofing the housing, etc.). I guess I just wanted to push that option to the extreme and hopefully discover that it wasn't likely to offer any mind-blowing sound improvement anyway, at least not in my situation.

Now if only there were some noise comparison data on the different range hood shapes... Okay, now I'm being greedy.

Thanks again, all.

OK viva99, let's add a little complexity now that the picture is simple clear.

Initially I wanted to simplify things. I didn't want to go down two paths simultaneously. But in your first post you didn't describe whether or not the wall outside would be an allowable spot for a remote blower (a box on the oustide wall), and furthermore all your questions were about _lengthening_ the duct run and adding silencers.... hmm so i kept silent about this one other option, described in the next paragraph.

A simple external blower will be quieter than an "in-hood" blower, because it's a foot or two away, and because the vibrations (noise) it will make will be dampened by your outside siding or brick. It could make sense to have a remote blower. It could work fine, for you, your budget, your CFMs and your noise target. Yes, "...even if it's a short run from your hood to the outside..." ("just the thickness of the wall, basically").

HTH
-david

David - Your second paragraph, is that based on assumptions or solid evidence? I'm only asking because it would be a shame to send somebody down a more expensive, complex, aesthetically unpleasing path based on a theoretical guess.

By the way, a while back I called Fantech with a question about their silencer, and in the conversation the rep said that with runs over about X feet air noise gets to a level where they recommend a silencer. (I forget exactly what X is, but remember thinking I was just about at the brink, which would be about 15 feet.) This would lead me to think that adding duct length so that you can benefit from a silencer doesn't make a whole lot of sense.

Thanks, David; I welcome any and all curve balls. Now's the time! But I confess I'm not clear as to how a remote blower will lessen noise if it's not actually remote (a foot or two seems pretty insignificant to me). Especially if there is no silencer involved. And I'm not sure how my exterior siding would dampen the noise. Won't most of the noise be coming through the vent/ duct? Am I missing something?

During my initial research, I copied the following sentence from one of these GW venting threads: "I have generally read on GW that it takes a minimum of about 6 feet of duct to get any effective noise reduction going remote. "

I think the actual quote is from breezy 2 (thanks, Breezy!), but whoever it was seemed to be paraphrasing many.

David, do you disagree with this? What about other posters who are generally skeptical of internal blowers' capacity for quietness? Clinresga? Anyone?

Ya think, thanks for that interesting tidbit longer duct lengths requiring silencers. After the previous round of responses, I had ruled out adding duct length for the sake of putting more distance between my hood and the blower and adding a silencer. Given the financial/aesthetic downside, I would have to be pretty convinced that this would reduce the noise substantially, and nobody seems willing to make that claim.

So the question remains: should I go with an internal blower or spring for a remote blower that will reside a foot or two away? All thoughts welcome and appreciated! This is extremely helpful (and not just to me, I suspect). Thank you!

How about calling someone that makes both and ask for their recommedation. Broan and Prestige come to mind. This is their business, so they might actually know what they are talking about as opposed to a range company that just slaps their logo on a hood.

Great idea, ya think! Why didn't I think of that? (Your name is so apt in my case). I'll let you know what I find out.

I think in the end you will be best served by taking the advice you obtained from this thread and using it to discuss your particular installation issue with an experienced specialist, someone who does rangehood installations for a living, not a general contractor whose level of expertise is likely to be less than yours, after all you've learned from these forums. A general contractor will always advise you to do what it easiest FOR HIM, not necessarily what is most beneficial to you.

haus proud -- excellent point. I wasn't planning to get advice from a GC, only from a manufacturer (or 2 or 3) that makes both internal and remote blowers, as ya think suggested. Since these manufacturers are neither inconvenienced nor ruled out by either choice, they "should" give me an impartial answer, no? And pretty well-informed too, I would hope. (Of course a big difference in profit margin could factor in, but I don't know anything about that. Anybody else?) OTOH, that's a great suggestion about asking someone who INSTALLS rangehoods for a living. Just have to figure out how to get hold of one in my rural neck of the woods. (Not much specializing going on around here; everybody seems to do a little of everything.) Thanks for the tip!

No-one has ever said that a blower remote by 24-30 inches would be louder than an in-hood blower.

No-one has ever said that, compared to an internal blower, a remote blower makes more noise just by turning on its axis. So it is not noisier to start with.

I can't say whether it's worth it or not worth it until you have a longer distance; viva99, you quoted someone saying about 6 feet length. That could be what starts another "rule of thumb" law.

All I can add is that in-hood the blower is an actual turning motor located at 10 or 20 inches proximity to your ears and 2ndly, not separated by any membrane. But a blower positioned behind your house's exterior wall is farther away, and from that fact alone could be half or a quarter as loud without even the wall being taken into consideration, and 2ndly it will be behind a physical barrier ( a real solid wall) so its noise will be reduced by another factor. It is true that noise can reverberate in a cylinder (your duct tube) and you may hear the blower or some harmonics of its frequencies, as noise coming back through the duct. Tape the duct with any stuff that is gooey or gummy to dampen the duct's musical vibration-ability. Please note that the hood shape can also vibrate a bit and produce some sound too; this is worse when the motor is closest to it.

It's a good question to ask to what extent one knows something from solid evidence or from extrapolating from assumptions. Unfortunately I don't feel comfortable getting into descriptions of my qualificiations here; suffice to say that I have not built two simultaneous houses with only the blower as the difference, and I have not replaced a high quality internal blower with a similar quality external blower over a 20"-30" duct span; neither am I going on pure assumptions in the abstract, as I have a lot of ability to spot vibration (noise) and eliminate it, and I believe the preceding months of posting testifies to my experience.

HTH
-david

I spoke to a Prestige representative the other day (from Signature). While he mostly dodged the question in the subject line -- unless I was too thick to get his answer -- he did acknowledge that a remote blower at a wall-thick remove from my hood might not be much quieter than an internal blower. The point he kept coming back to was that a short, straight duct run would allow me to run the blower at much lower speeds. He spoke enthusiastically about the new Kobes, which are equipped with some new "silencing" technology. They have 4 speeds, the lowest of which is called "quiet". He seemed to think I would be running my blower on "quiet" 90% of the time, thanks to my short, straight duct, thus rendering the whole sound question moot. Of course, I'd be foregoing the variable speed control you've all been recommending, but Signature rep didn't think I'd miss it. Hm. Is he being overly sunny?

David, I'm appreciating several of the points you made, but find myself unable to grasp one or two. For instance, if the remote blower is directly behind my hood with an open airway connecting the two, how does my exterior siding come into play? Also, is the fact that an internal blower PUSHES air out, while a remote blower PULLS air out... does that make the latter quieter, regardless of the distance factor?

I'm probably revealing a tragic level of ignorance here. If so please forgive me. And move on. For your own sake. Otherwise, thanks in advance for any clarification.

I currently have one of those old-school, exterior wall mount one speed chain pull kitchen fans. Remember those? At normal standing distance from it, about 2.5 feet, verus taking a big step back, I notice no discernable difference in the noise level. If I take another big step back it's definitively quieter, but not by some crazy margine.

I think it's human nature to come into this forum not knowing much about anything, reading many people's opinions and perhaps gathering up some facts of your own, and then suddenly come across as a subject matter expert in posts. I'm not accusing you of this, David, but I do remember some of your initial posts just a few months ago. I, for one, try to be very clear when I'm offering a theoretical guess versus quoting opinion, versus quoting a fact from an authority, versus quoting a fact from my personal experience. I just like to be careful when I could be spending other people's money. Here's some food for thought:

The hood at my mom's that I referenced in an above post and elsewhere: After reading this forum for quite some time, I was extremely shocked when I took out her MESH filters and noticed NO noticable difference in noise between when the filters were in place versus when they were entirely removed. This begs the question, how much quieter are baffles versus mesh? From reading this forum you'd think it's a night and day difference. Not MY experience, unless baffles are somehow quieter than free air.

Viva - The only thing that I have left to add is to reiterate that my mom's blower does just fine on half the speed of Kobe's lowest setting. Makes you go "Hmmmm."

We are definitely hitting the limits of my knowledge and experience here.
At low speeds, I don't know.
At high speeds, I don't know.
Whether an air-pulling blower is quieter than an air-pushing blower.
What I know: in 2008 nobody said the noise is greater, AFAI have read, and I'm usually thorough.

I recognize that the distance is only a few inches, so let's just leave it at " you still have that option" of a remote blower, which is why I raised it in a recent post. Whether the wall helps dampen noise will depend on the shape and position of the blower; it could be that the wall will have no dampening effect.

It is true that some will say my writing sounds SME-like. What can I do now? In other threads I have issued long caveats not to take any action based on anything one reads here posted by myself (or any other internet stranger.)

viva99, if you can only get to see a 4 speed one, gee, well, you might be very happy with it. The salesman is right that you would have it on low 90% of the time. It is good to leave on for a long time and when it's pleasantly quiet it's a pleasure to have it "on" practically all the time.

HTH
-david

Thanks, ya think and David. You've both been really helpful, whether by introducing variables I hadn't thought of, or by bringing everything back down to earth through personal experience and common sense. I'm the kind of person that likes to juggle all the complexities for a second or two, just to get the feel of them, before tossing most of them away and getting back to basics. That's why this forum is perfect for me (maybe a little too perfect).

I was at a friend's house for dinner last night. He frequently cooks fantastic meals for 10-20 people in his newly renovated kitchen (his cooking was just as great in his funky old kitchen, BTW). He has a 3-speed Best internal blower inside a 48" hood over his 48" range, venting directly through an outside wall. He knew nothing about it -- just bought what his range seller told him to buy -- and is very happy. He pointed out how well his hood was sucking up all the pasta water steam. It really WAS impressive. He told me to stop obsessing. I said, "What?" He yelled, "Stop obsessing!" See, it was hard to hear him over that fan.

viva99, you are a great evaluator and funny too.

one more reason i like a remote is to have more cabinet space above the cooktop.

-david

viva, back in 2007 I was in the same position as you and asked many of the same questions. I spoke with a couple hood mfrs and was persuaded that it would not make sense to incur the added expense of a remote blower in a straight out the back and through the wall venting installation for the marginal, at best, reduced noise over an internal blower. The consensus was that the noise levels would be comparable. I ended up getting a 1200 cfm internal blower (actually, 2 600 cfm blowers) 42 X 27 Prestige proline hood, over a 36'' BlueStar range with grill. Is the hood whisper quiet? Not really. But it is correct that I leave it on the lowest variable speed about 90% of the time (unless grilling, woking or searing) and at that speed it is quiet enought -- easy to carry on a conversation, watch tv or listen to music. I'm fairly noise sensitive, and I wish the vent were silent. But it works very well and overall I am satisfied.

Good luck with your decision.

r.

"Also, is the fact that an internal blower PUSHES air out, while a remote blower PULLS air out... does that make the latter quieter, regardless of the distance factor?"

Viva - now you're delving into the realm of the utterly ridiculous. Hoods and blowers are complicated enough to size properly to capture fumes and grease, overcome static pressure of duct design and exhaust efficiently. Add to that an aestetic component, cost, and usually sound, and things get even more dicey. When you throw in caveats like is this brand louder then that one or this design more efficient then that, you are venturing into uncharted territiory.

The vast majority around here , and all that I can tell in this thread can only offer advice based on experience. No one is going to have run the testing and computations for the stuff you are asking about , let alone have conduct it on multiple brands. Much would be moot anyway because, it won't have taken into account your SPECIFIC site conditions and ducting materials.

You really need to hire a kitchen designer with EXPERIENCE designing venting systems , or probably better - get an engineer to evaluate your conditions/criteria/prospective brands.

To answer your question: noise on push vs. pull will depend on whether you are comparing the same fan in the same duct, or the specifications of the different fans you are comparing. You'll also nee to take into account the actual design of the fan, and exactly how are the ratings derived? How stringent is the CFM and sone or dB. rating of the fan's manufacturer. A fan from Broan rated at 600 CFM and 2 sones is likely to be better than one with the same specs from Xiansaodong Wi Fan Co. from China. Both are likely to be inferior to a product from O + F out of Germany.

With your very short duct run, just about anything you get will be adequate to exhaust fumes and hot air from a 36-48 pro range, you don't say your cooking source? Adding a 90 bend and a few more feet of duct isn't going to tax remote blowers or even require an upsize.

Probably the best avenue for you is to visit showrooms and distributors in your area that have hoods installed and pick one that meets your sound requirements. Most will not have a remote blower/hood setup.

"You really need to hire a kitchen designer with EXPERIENCE designing venting systems , or probably better - get an engineer to evaluate your conditions/criteria/prospective brands."

Yeah but antss, what are they really going to know? The engineer might look at the charts that the company publishes, but I think it's fairly established that unless the hood is HVI certified there is no standard between brands. Now how many of the popular brands are HVI certified?

The kitchen designer, what can they really bring to the table beyond their own experience with hoods? As you say, different applications will have different results. But if your customer says to you, "I want the quietest 1200 CFM hood setup available, I don't care what it costs or what it looks like," with all your experience wouldn't you be able to give a strong recommedation without asking questions like "How many elbows will there be, because I'm going to say Broan if it's three or less or Air King if it's four, Prestige if it's five or more?"

In short, taking the remote versus internal versus inline out of the equation for a moment, I struggle to believe that there is no fairly definitive answer of what hood will be the quietest, relatively, in ANY typical installation.

Now put back the remote versus internal, and specifically Viva's couldn't-be-simpler not to mention not-very-unique application, what other factors could possibly come into significant play to where someone who's seen a bunch of different applications of a 1200 CFM exhaust can't definitively and in good conscience recommend set-up A, brand B, over anything else they've seen?

I'm just trying to understand what a "professional" will have to offer other than his anecdotal experience, when it comes to the actual equipment. It's the same conversation when it comes to dishwashers. Yes, proper installation comes into play. But can you really walk into a kitchen and say "Normally I recommend Miele but in this kitchen an Asko will be quieter."

"Now how many of the popular brands are HVI certified? "

Not many - simply because the industry just agreed (reluctantly) to adopt consistent measurement of their products. Participation is not mandatory either.

The engineer will the units. You'd of course be paying for these and teh professional time , but if you're this obsessed, that's the way to go.

"In short, taking the remote versus internal versus inline out of the equation for a moment"

You can't tke it out of the equation - Viva is considering it and while one brand might have the quietest setup with an internal powerpak, it may not be as quiet as another brand's external setup. Simply put there are TOO many variables to come to an accurate conclusion. Add things like: "is a push design quieter than a pull design or is axial quieter than radial" and things get exponentially more complex.

"wouldn't you be able to give a strong recommedation without asking questions like "How many elbows will there be,"

ABSOLUTELY NOT, NO WAY, - this is one of the first things that needs to be calculated and factored in. Otherwise you cannot even begin to rec. a system. If I just sold you a Broan 280 CFM external blower, it'd be quiet but probably wouldn't pull out the smoke from your Viking grill even if it were simply 1.5 ft. away right behind the hood. Mount the thing 36 ft. away on the roof with a few elbows and it might not even overcome the static pressure of the ducting let alone exhaust the steam from your pasta water.

I think you completely missed my point.

If someone asks how many CFMs they need, then most certainly the cooking equipment, length and route of duct run, etc. all come into play. Yes, I can see where you may determine that someone needs to move 600 CFM, and then due to the particular application you'll need a 1000 CFM fan to accomplish this. Understood.

But my point and what I'm asking is this: Viva has about as straight forward possible application as can be imagined. The only variable that hasn't been established is desired CFM. What more needs to be known in order to answer the question of whether remote makes sense in this case?

As for leaving the remote versus internal out of the picture, I said that not for Viva's question - as this is of course exactly what he's asking - but on a broader level: If I tell you I'm looking for a recommendation for a very quiet 600 CFM (rated) internal blower hood, do you really need to ask me twenty more questions? Is it really possible that brand A will be quieter if there's X static pressure, and brand B will be quieter if there is Y static pressure - to any degree significant enough to where it would keep you from being able to make a safe recommendation?

By the way - you said "The engineer will the units." Clearly a word missing?

In case any of this isn't coming across right, to be perfectly clear: I'm not arguing, I'm asking. Not just for me, but for anyone else who gets frustrated when they can't seem to get a straight-forward answer. Thanks!

Interesting discussion, antss and ya think. To be clear, antss: I asked the pulling air vs. pushing air question because someone else had introduced the idea in an earlier post and I didn't get it. I had no intention of further complicating the issue, much less "delving into the realm of the utterly ridiculous." But it's true, the whole discussion CAN get pretty ridiculous if one keeps adding variables before ever coming to a solid conclusion about any of the variables that came before. Intuitively I agree with ya think: one SHOULD be able to say who makes the quietest 1000 cfm internal blower, period. One SHOULD be able to say whether a remote blower is inherently quieter than an internal blower by virtue of its design (i.e. over and above the fact of being further from your ear). These questions don't seem all that complicated to me. Some can be answered on a showroom floor, as has been suggested here. Others, like how remote a remote blower has to be in order to measurably reduce noise, seem pretty straight-forward too, although only a manufacturer/venting contractor/engineer is equipped to investigate. Alas none seems inclined to do so, at least not in any way that's accessible to lay people like me.

In my own case, I have made an executive decision not to add more duct to the outside of my house. I will entertain the idea of a not-so-remote remote blower a bit longer, but if the jury is still out on this, I will go internal, because it's the cheapest and easiest and least ugly solution. And then I will begin the hunt for the quietest internal blower I can find. (For those who asked: I'm looking for something in the 1000-1200 cfm range to go with the 42" X 24" hood that will hang over my 36" AG range that will have a maximum heat output of about 90,000 BTUs to be used for occasional searing and stir-frying, no grilling.)

Again I find myself humbed by all the impressive brain power that's gone into this thread. You people are amazing. (And BTW I wasn't kidding when I wondered aloud which hood shape was quietest... anyone care to wander into THAT thicket, hmmmm?) Thanks!

PS -- reposado, thanks for sharing the fruits of your own research. VERY relevant and helpful. And congratulations on finding a solution that works for you. Hopefully I'll be right there with you. Soon!

Humans think they are able to understand almost anything.
They think they can build instruments that will answer their questions.
Problem is, they often then give away too much power to their measuring instruments.

So far in observing the development of human society, we note they now measure Noise in dB, dBa, dBrN, dBrNc, dBrNco, dBs, etc -- but then humans are unable to manipulate these units to reach conclusions that become socially accepted norms.

Parameters measuring Low-noise Environments elude them.

Insight from an observer.
HTH
-david

Some thoughts on the relationship of noise to pushing or pulling.

In the kitchen ventilation scenario, whether a blower is pushing or pulling, the differential pressure is so small that the number of air molecules on either side of the blades is about the same whether pushing air or pulling air. Without doing the experiment, my guess is that at a constant differential pressure, the noise is negligibly different between the two cases. Generally, the fan doesn't "know" whether the static pressure difference is due to pulling or pushing.

This does not mean that there aren't differences in noise between different blade designs for particular flow rates and static pressures. Broan/Nutone's quiet bath fans, for example, use squirrel cage designs with many small blades, much like designs used in automobile air conditioning blowers (at least the ones I'm familiar with) and VAH kitchen hoods. The 1500 cfm (at zero static pressure) Broan/Wolf roof-mounted exhaust blower looks like a squirrel cage blower on steroids, with many fewer but much larger blades.

Paddle shaped fan blade air movers are common, such as radiator fans in cars and ceiling mounted whole house ventilation fans. These do not usually have to be designed for low noise, but for high flow and efficiency. They have higher turbulence around the blades and more noise. Some inexpensive kitchen wall exhaust fans I've seen use these.

There are also axial fans for inline use in ducts. Tiny ones sometimes use paddle-shaped blades, but the larger types are more related to the compressor designs seen at the front of a turbojet engine; they are bounded by the outer wall and do not have room to shed vortexes off of their ends as much as paddle blades do when pushed to high tip velocities.

What is different about pushing or pulling air is that at the extremes of pressure differential, one can only pull down to vacuum (one atmosphere) but push up to several or many atmospheres. In both cases, significant static pressure differentials are achieved using positive displacement air pumps, such as the piston types common on small air compressors, or the Roots type blowers seen on drag race car superchargers and used (in some form) on large industrial air compressors.

For residential use, one wants the pressure inside the house to be close to the pressure outside the house. This may require make-up air. The hood exhaust blower, then, only has to work against the static pressure of the ducting pressure drop, the hood filters pressure drop, and the losses due to the transitions from inside to hood and hood to duct. Since the pressure drops are associated with turbulence, noise will be caused by each of these elements, as well as at the fan blades themselves.

kas

................................see how complex it can get if you actually want to know the details and for them to be accurate!

Kas, you said a mouthful. And very eloquentlly, as usual. If I ever wondered just how complex the issue really was, I can wonder no more. Thanks for taking the time to lay all of this out for us laysters.

Antss, I've been schooled. (On the complexity factor). Guess I was really asking for it, huh? (Yes. I was, actually.)

David, thanks for putting a philosophical spin on things. I guess that's the best way for me to approach my own particular fan noise quandary-- philosophically. As in, que sera sera.

FWIW, we've just decided to downsize our range purchase -- from 36" to 30", and from 90,000 BTU's to 60,000. (It's just so rare that we ever need more, and we could really use the extra counter space) This might produce the side benefit of minimizing (literally) our hood concerns. We'll see.

Nothing wrong with an education. I know a few folks that attended law school because they though it'd be fun, never intending to practice.

SO, what did you decide to go with?

Kas - I love your lessons, sometimes I can even follow! Maybe you can answer this question from a practical standpoint:

Let's say someone tells you they want a 36" 600 CFM hood and the exhaust route is up two feet and then straight out the wall. Now let's assume you've had considerable first hand experience with many different hoods. What additional information is needed to recommend a brand or setup that will be among the very quietest?

I have a Broan 6400 Rangemaster Elite with a remote blower and I love it. But it is not silent. When it's on high, I do hear a lot of noise, but not motor noise. It's all noise from air moving. My ceiling is 13' high at my cooktop so the pipe exits the top of the cabinet and runs up the wall about 4' before disappearing into the attic space. I have not built a chase around the pipe yet, but will insulate the pipe when I do get the chase built. I think that will greatly reduce the noise I am hearing. that being said, this hood is so great that I rarely ever run it on high. It is variable speed so i can select a low (and nearly silent) speed for almost all of my venting needs. Because the blower is remote, the hood is pretty low profile. It has halogen lights in the front and warming lights in the rear.

Very, very nice, ccoombs. (And the rest of the kitchen ain't too shabby, either!) I am definitely focussing all my hood optimism on the low setting. Thanks for the affirmation.

Ya think: great, economically worded question. All I really need to know at this point. (You, too?)

Aantss: I'm hoping to order the range itself today -- probably a 30" American w/ two 17K BTU burners. Then it's on to the range hood. I'm thinking a 36" X 24" with an internal variable speed blower that goes up to at least 600 cfms. Should be enough for 56K total BTUs, right? As for the "shell", I really like that quarter-barrel shape that's all one width and 2 or 3 feet high. Modern Aire makes a black one with stainless trim, just like my likely future range. I think it's called a PS 26. Independent's "Bonanza" model is similarly shaped, but doesn't come in colors or variable speed. (Did I mention I'm as picky about aesthetics as about noise? Heaven help me...) Downside of Modern Aire is I'd have to buy one sight unseen -- or rather sound unheard -- which would be a little ironic after all this...

Which reminds me: do any of you experts, or hood owners, know if this barrel shape should be avoided for any reason?

Here is a link that might be useful: {{gwi:1392923}}

When the effluent rises it has some velocity, and hence momentum. When it enters the hood it has a tendency to "reflect" and curl downward and potentially escape. If the hood is deep enough (top to bottom) and the hood fan flow is high enough (cfm) the curling effluent will remain captured and will be exhausted. The barrel design in the picture looks to me (without examining one) like it has adequate depth.

W.r.t. ya think's question a few messages up: First I would say that the change from vertical to horizontal should be as large a radius curve as you can fit to minimize pressure loss (as well as noise). The effluent momentum (which is a vector) is being changed in direction. This is akin to stopping it and starting it up again. If it can slide along a curve, the momentum loss is significantly less. There is one commercial ducting source I came across once that uses 90-degree transitions, but embeds a curved shape within the duct to improve the flow.

I find it hard to answer the question of what questions to ask. Usually, the answers aren't available. Ideally, one would want to know the fan curve (flow vs. static pressure) and try to estimate all the pressure losses (including the pressure one might pull the house down to with or without make-up air) to see what the real maximum flow rate will be. This can then be compared against estimates of effluent generation rate calculated from the reference below. The power used might be adjusted to represent your cooking style, as rarely would one have all burners on maximum and cooking at the highest pan temperature. One thing is certain, flow rate in the hood has to at least equal the flow rate from all the active burners and pans, and arguably should be higher due to imperfect effluent collection.

Implied above is that the hood manufacturer can supply pressure loss of the filters vs. flow rate, as well as that of the hood transitions. Getting that data, even if it were ever measured, would be unlikely, me thinks.

I suggest that various hoods be "audited" in showrooms to gain a feel for their noisiness versus their designs.

The reference worth reading, even if one doesn't intend to use it for calculations, is "Thermal plumes of kitchen appliances: part 2 cooking mode," by Risto, Hannu, and Pekka. (I've found it on-line whenever I've looked for it. Part 1 is also interesting.) If you do use it for calculations, please note the following apparent errors in their Equation 1:

The constant should be 0.05 not 5.
The units of phi should be kW, not W.
(these corrections make their tables consistent with the equation)

You will need a scientific calculator or counterpart software to do the exponents (unless you are very old school and know how to do logarithms). You will also need to convert BTU to kW and cubic meters per second to cubic feet per minute. This is left as an exercise for the student. [insert sociopathic laugh here]

kas

I've been a regular reader of this forum for far longer than my registration date implies. I struggle to think offhand of one case where someone installed a good conventional hood (i.e. a ducted, not OTRMW, not downdraft, etc.) with range manufacturer recommended CFMs and came back complaining that it wasn't doing an adequate job of venting. The closest I can recall is someone who lowered their hood from 36 inches to 30 (or something like that) to improve performance.

On the other hand, there have been plenty of complaints about noisy hoods. So while all this engineer talk makes for interesting conversation, it does nothing to answer a very simple request: a recommendation for one of the quietest hood options in Viva's very straight-forward application. Oh and by the way, can someone with first-hand experience weigh in on whether a remote blower makes sense in this case?

Again, I really do dig the physics lessons. But if a KD or engineer tried to bill me by the hour for this, they'd be fired on the spot as it borders on absurd from a practical standpoint.

Making a low-noise product.
Making a product whose noise is deemed good.
---
Millions of people have asked this same question, as buyers.
Thousands of businesspeople and thousands of their employees have wondered how to make a product that would meet this simple demand.
---
The more you analyze noise the more you see it is just a batch of scratches on your instrument screen, more at some frequencies than others.

When you really study what noise is, you see that deciBels are not good instruments. They make a relative scale. Relative to what? Until you or I or a bunch of us pick a reference noise as a starting point, it is just idle talk to discuss what is quiet, and what quiet is. A reference noise shape.

The quieter you get, the more you end up measuring miniscule vibrations which don't bother many people and do bother some. Then you end up discovering that it is all in the ear of the beholder, whether a noise is quiet "enough" or pleasant "enough". Then you end up discovering that any other continuous noise in the background immediately changes people's perceived threshold of acceptably quiet noise in the device you are focusing on.

It's so relative, that the best advice is to play background music or plan for some background hum.

Have you ever lived in a concrete building? They are much quieter than wood-frame buildings. That should be great news. Problem is that then your kitchen fan sounds louder, because the background ambient noise in comparison is quiet.

When you move a large quantity of air it will make a fuzzy noise.
At first, it will sound good, at at low speeds.
Then, at higher speed, it will sound different.

"One of the quietest hoods" is a great question, but it has no answer.

HTH
-david

Yes, we all have different ideas of what is loud or what is quiet. But someone who has observed, first-hand, several different hood applications in fairly straight-forward installations should be perfectly capable of saying which they've found to be among the loudest and which are among the quietest without testing equipment. Some people think Ventahoods are loud, others would argue that they aren't. But would anyone question that clinresga's Modern Aire setup is significantly quieter than his/her Ventahood?

What do you think would happen if we took a survey asking people to choose between:

a) a hood that is quiet enough at normal levels to encourage daily use, but might let a bit of smoke escape under the heaviest conditions

b) a hood that's annoyingly loud to where you really don't like to turn it on, but when you really need it - like searing six pans of steak at once - it won't let out a lick of smoke

Of the two, I'd prefer A, and I'd be surprised if most people wouldn't feel the same way. My personal experience with Ventahood is such that I know I wouldn't turn it on much. So when someone like clinresga comes here to share experience with a much quieter setup, THAT to me is helpful.

Let's not forget one other variable in this discussion - cost! Most of us live in a world where $$$ are in finite supply, and we have to find an optimum balance of performance vs cost. For those of us in the far north, the infrastructure requirements to install a higher capacity blower than we really need, simply so we seldom have to run it on max, render the concept quite absurd.

Good point. A lot of cooking might be "fine" under a gentle fan drawing X (less than 100 CFM).

Doubling or tripling it, going to 200 CFM, you start needing to replace the air your fan is sending out its chimney.

Going from 200 CFM to 400 CFM is another doubling, and it absolutely requires make-up air -- What can you do "in the far north"? You can open a window and that only works for about a minute or two when it's below Zero degrees outdoors. I think the vast majority just wait until summer before frying salmon again. If your house is very modern, your whole house Heat Recovery Ventilator (HRV or ERV) takes care of the new air required.

Going from 400 CFM to 800 CFM is another doubling. Talk about lunacy. Unless you've got the air. I agree with you, cooksnsews. We need these more moderate points of view, so I'll be one of the first to thank you.

I'm eager for more comparative anecdotal evidence too ya+think.

-david

Hi Viva99

So what did you end up buying and are you happy with it?

Regards

mark