External blowers reduce motor noise at the hood. but unfortunately that is a small portion of the noise you actually hear. As you correctly point out, the airflow noise is much louder and the only way to reduce that is to move less air. The other big con to external blowers is servicing them is a pain. The only time I think they're worth it is if you need to exhaust more air than an internal blower is capable of. Too many CFM is a bad thing - I see the hood you linked is available in 600 or 1200. Over a 30" range I would go with 600 (and stick with an internal blower for cost effectiveness and ease of service). Best has more styles than Broan, but if the one you like is available under Broan and cheaper go with that.

External blowers may or may not be harder to service than in-line or in-hood blowers. (The former depends on the roof configuration, while the latter case has to include risk of damage to the cooktop. In-line may be easiest to service if the attic space it lives in is large enough for it and the servicer.)

External and in-line blowers potentially allow for use of in-line silencers (mufflers). Noise comes from baffle turbulence, transition turbulence, duct turbulence, and blade tip turbulence (at the higher frequencies), and motor and duct rumble/vibration at the lower frequencies. A more powerful blower running at part speed will have much lower blade tip turbulence noise (which will probably dominate most configurations) than a smaller blower running full speed to achieve the same flow rate.

For six square feet of [actual] aperture, I would aim for achieving an air flow capability of 540 cfm, which given various pressure losses over the air loop from baffles to outside to make-up air path to baffles, would likely require a blower of about 800 cfm rated performance at zero inches w.c. of static pressure (i.e., hanging freely in the air).

Yes, a piece of something cleanable, such as stainless steel from a local sheet metal shop, would make a suitable filler strip. I would recommend if the aesthetics allow, that it not be horizontal, but angled from hood aperture edge to wall such that rising cooking plumes reflect upward. The necessity for this depends on other factors such as side cabinet configuration. You don't want the effluent to reflect down and spill outward.

kas

I have a Best Hood with an internal blower and 1100 CFMS over a 6 burner 36" Wolf range top. I find it to be very quite and reduces grease and odors very well. I have been very happy with it. We did not do make up air, no problem. And it is very easy to clean, baffles go in the dishwasher.

Thanks all!

That does look nice, Kalapointer, but everything else in your cooking area is so pretty you could have gotten away with a cardboard box! Quiet is also good. We were looking at that model too, probably because of your photos. :)

I expect to use lower speed for most cooking, but would like reserve oomph available. (For example, exactly half my household will have asthma induced if habaneros are being processed without thorough ventilation.)

So the same amount of suction from a big fan should be quieter than from a small one, correct? So I should try to avoid the ones with 2 fans, if internal?

I've never had to have a hood serviced but I guess I should keep that in mind. The attic will not be comfortable and might not have room for a silencer (I admit I have no idea how big those are). And I probably don't want extra stuff on my roof facing the front of my house. I DO like the idea of simply replacing a blower in the future to having to rip out the hood; maybe having the functional parts somewhere that isn't cosmetically important is worth the inconvenience or some guy having to bellycrawl in my attic.

I'll have to run this by my GC, but now I have a better idea of what to run by my GC!

I doubt that we will need MUA--the kitchen will be open to the rest of the house which is anything but tight--but we might be required if the permitting office can figure out what it is...

I appreciate all the advice. Thanks!

One more thing guys.

DO not forget to provide adequete MUA

Interesting!

Which model did you have? How was it situated? What did you replace it with and are you happy with it?

Fori, Thank you for your nice words. We didn't want a vent on our roof either so the inline blower is in the space between the ceiling and the roof and then the duct work makes a turn towards the back of the house. If it needs to be serviced, we can get to it through an access in the ceiling in my pantry to the attic where the blower is housed.
I also use the lower settings most of the time and if I am making a lot of smoke or grease spatter I turn it up higher. The power is there when you need it. It is so quite on the lower end, that we have left in on all night and didn't realize it was even on.
Here is the vent on the back side of our house.

Chefwong and fori, The model is WP29 and it is an in-line blower not an internal blower. That was my mistake using the wrong terminology, sorry. I have never had the controls clog up. The MUA is not an issue in my house. It is a very open floor plan and I have lots of windows to open if i need.

I have a Tradewinds Hood.

Kala - I hear what you're saying and even on a not so tight house, MUA is important. Alot of people just overlook it. Proper Vent/Exhaust design is important. Oftentimes, it just becomes a backburner item in the design/install of things

Thanks Kala. That looks like a really good setup.

C'mon, Chef! You're not sharing nearly enough information for one to learn from your mistake! :D

While I dislike the MUA code it's to make sure you are safe. I think people shouldn't just dismiss it saying they will not have an issue. Remember, it's there to prevent backdrafting exhaust from your water heater/furnace/dryer and any other Carbon monoxide sources into your house. Is it worth the chance with your family?

CO is odorless and clear. By the time you think you have a problem to open up a window you my be pasted out on the floor.

Unless you are 100% sure you will not be pulling exhaust into your house I believe you should at least consider it. If you are going to by pass it, make 100% sure by testing your house to make sure it's leaky enough to keep up with the air being drawn out of the range hood.

On my Best by B, I did a simple test. Boiling Kettle of water....watched as the steam went through the front lights more than through the baffles....

MUA is important. Either via a seperate switch or one that comes on via a sensor that opens up the servo/dampener after a certain CFM. We have a 10 duct exhausting _ and a 10 inch under the stove for MUA

Trivan, Our only source of carbon monoxide gas would be the water heater which is in the basement at the other end of the house and it is vented outside. Our heat source is radiant floor heat which uses the hot water from the water heater. Everything else is electric, so I think we are ok without MUA. But I understand your concern that people need to know why MUA is important.

Best by Broan has many models though. It would be helpful to know which performed so poorly, as well as its position relative to the cooking surface. I can't write off an entire (large and generally well-reviewed) hood manufacturer based on that!

If the house pressure falls below 0.03 inches, you may get back-drafting of your water heater. If the water heater is given its own MUA (if a kit is available), then lack of deliberate kitchen MUA only affects actual hood cfm. There is always MUA that exactly equals what the hood moves outside; the question is where does it come from and what pressure drop results.

kas

I'm sorry, there are certainly situations where external blowers are easier to service than other situations, but I can't think of an easier-to-service setup than an internal blower. I won't deny that there are some sound-saving opportunities that are available with an external blower, but really, how many hours per day do you run your hood on a high enough setting for it to matter? In my opinion an internal blower is the best setup for the vast majority of homeowners. Keep it simple!

Makeup air if it exists should always be interlocked directly with the hood, not run off a separate switch. I think Broan lets you interlock the controls of some of their model hoods directly with their dampers, but otherwise a current sensing relay or sail switch could be used.

I still believe more than 600 CFM is overkill for a 30" range, even if it is pro-style. Yes, running a 1200 CFM hood on low is quieter than running a 600 CFM hood on high. But running a 600 CFM hood on low is much quieter than either of those and is what the OP will likely need most of the time. Yes, by going with 600 CFM you won't be avoiding the makeup air requirement, but if you're in a climate that gets extreme temperatures like I am, you're going to be concerned about how much outside air you're bringing in. I only have a standard size electric range so I don't need to worry about a powerful hood and makeup air, but if I did, in the middle of the winter I would want to be bringing as little 10 degree air into my house as possible.

I agree with Chefwong that CFM is not the only thing that matters. Capture area and hood design are key too. I have a Broan hood and it works great, but maybe my model doesn't have that design flaw, or maybe I'd notice it if it had a more powerful blower. I don't know.

We have no idea what the design flaw is, or if the hood was even installed to manufacturer's specs. Chef hasn't shared that information.

hvtech42 wrote: "Makeup air if it exists should always be interlocked directly with the hood, not run off a separate switch."

Certainly this is the easy path for a single vent system, but lacks control for different hood flow rates unless more control is inserted into the MUA path. Possible schemes would be pressure controlled dampers, motor control operating in parallel with that of the hood blower, etc.

I hope the "separate switch" interjection wasn't a deliberate Strawman argument, because I don't recall anyone recommending it. However, the "always" assertion is a bit strong; as it can only apply if there is only one vent to sense. Large building ventilation systems, for example, usually control MUA by maintaining constant pressure using pneumatic, fluidic, or electronic control. A house with multiple kitchen vents, multiple bathroom vents, appliance vents, and a fireplace, with variable seasonally open windows, can be better served by proportional control, either passive or active depending on the setup, and particularly depending on the pressure losses in the MUA path.

In any case, I recommend separate MUA for combustion appliances when any powered ventilation system is present that can exceed the house leakage rate at an internal differential pressure of -0.03 in.

kas

How about big holes in the floor open to the exterior under combustion appliances? I have that.

I'm really not interested in MUA. If I need it I'll put it in. This is not a small project and the expense of that is not going to register. (On the other hand, I am happy to get a cheaper hood if it's all the same.)

I've only ever dealt with powered MUA in commercial applications. In residential, just dampers that are interlocked with the hood. Yes powered ventilation is obviously more effective than passive ventilation, but a simple damper has done the job in any residential application I've ever seen, integrated with the HVAC system if needed.

The separate switch would only make sense if you were doing a separate blower which I think is overkill for most residential. As I said before, simple is the key! Simple design, simple to operate, simple to service. Most people just want to be able to turn the fan to a certain speed and get cooking. They don't want to futz around with a bunch of variable speed controls balancing exhaust flow with intake. And I'm never a fan of putting complicated crap like that into a house that only makes sense to the owner. You're going to flummox guests and future owners for no real advantage.

Of course, if you are going to connect to the HVAC system, you should have a HVAC person who can deal with that, including automatic blower activation if needed and making sure you're not bringing too much outside air into your return duct. This goes especially if you have gas heat. You do not want to kill your heat exchanger prematurely.

Makeup air has been a real problem in the residential appliance biz. Clueless salesmen/kitchen designers spec'ing these gigantic ranges and gigantic accompanying hoods (often that are too powerful for even the gigantic ranges), and they have no idea there could possibly be a consequence. Kudos to Broan for coming up with a prepackaged solution that does not require an engineering degree to understand and use, or any expert for that matter (although as I said above, an HVAC tech's help may be needed for some installs).

I guess you could rig up a dedicated blower and resistance heater for the kitchen, but most people I know would rather ditch the prostyle range than cough up the cash to install and operate that.

Nobody is "interested" in MUA. It is not a creature comfort. Either you need it or you don't. If you don't, there's no point spending the $$$ for it.

This post was edited by hvtech42 on Thu, Jun 26, 14 at 23:45

By "Not Interested" I mean that I am just looking for a hood. I am comparing these two lines of hoods. MUA is important yadayadayada I'm just trying to pick out a stupid hood first!

MUA is something that will be dealt with separately because it's not relevant to cabinetry design or anything *I* can responsibly select before I start my project. I'm ignoring it NOW but I am not ignoring it permanently.

Is the Broan package good? darn it. I am NOT interested! :P But If I end up with a clueless HVAC person, it might be easier to go with that.

OK, got it! I misunderstood. I'm not sure which Best model you're considering, but I assume one that looks like the Broan one you linked. Honestly if I were in this situation and I liked the looks of both I would pick the cheaper one. A lot of people, myself included, like their Best/Broan hoods, so I think either is a safe bet. Hoods are simple, there aren't that many differences between them or things to go wrong with them. In this case, I'd be willing to bet that the Best and Broan are exactly the same hood, the only difference being he logo and the price tag.