dont get a small liner/insert for a big hood. get the biggest size that will fit. I'd go with removable baffle filters. the insert is basically a box. it'll have a duct hole that can mount an "internal" blower or an adapter to mate with your ducting for a remote blower.

usually a hood will have some internal framing. find out what the dimensions are. someone is going to need to mount the insert and make sure it is properly installed with no gaps.

@Filipe Custom Woodwork - I actually have a good handle on what the range and room require as i plugged it all into a calculator. It's more trying to understand what the various pieces are and how they should be sized to fit inside one another.

Your photos help clarify a bit, so the insert sits inside the liner and it may or may not contain the blower as well, is that fair?

Why do you recommend BEST as a product? What features do you like about them?

@mishmosh OK that helps clear things up a bit...can you give me some idea of relative dimensions? Like if the hood is 66 what should the liner be? 66? 60? what about the insert? And is the blower always part of the insert component or do they have the blowers located further up within the ducting? (not talking about an external blower, I understand those live outside)

The insert is the blower. People use those terms interchangeably.

I do not recommend any vendor. Many of our clients use BEST as well others, but have noticed a trend with BEST. Please check with your appliance person in terms of what insert/blower etc fits you best. The above statement was worded wrong. We leave the appliances to the appliance vendors but have noticed trends.

Basically what you really need to relay to your appliance guy is the model number of the stove you have which should be purchased along with the hood/blower etc. At the time of purchase they will let you know what you need. You also need to let him know the dimensions of the wood hood/or stucco hood etc you are intending to use as well. you need to go and see these work and hopefully they have functioning displays so you can hear the noise etc. Do not purchase online unless you have already spoken to an expert and know what you are looking for. Based on the size of your hood are you using either a 48" or 60" range? Are they the professional kind because they will need a LOT of CFMS = noise.

@Filipe Custom Woodwork

I think you misunderstand what I'm seeking a bit. I don't have an 'appliance guy', I have a contractor who is doing the kitchen and will be in charge of installing the hood and ductwork and I have a fabricator who will be building the outer shell of the hood to our specifications. The contractor has already run all the numbers and told me the required CFM (at least 1000, 1200-1500 even better) and the fabricator will put any insert/liner we chose into it. What I am trying to figure out is what physical size the insert/liner/blower should be given a 66x28 inch hood. I know you said you don't support any particular vendor but if you have examples of what I should be looking at for my range hood size that might help me on my search.

I understand perfectly. You are in charge of purchasing the appliances right? If the answer is yes then you have to go to an appliance store, hence appliance guy or is your contractor purchasing the appliances, if he is then I would still make sure you know what you are getting and the model #'s etc.

The numbers he gave you are to be expected. The physical size depends on what I have already said on my last post which is a conversation you need to have with the appliance vendor. The appliance vendor should be the ones installing them too. this is what we have our clients do so there are no mistakes etc.

>I understand perfectly

No you really don't. It's OK, I got the basic information I needed, I'll do some more research on my own

This is also an issue of a standard insert/liner, such as Wolf or others might sell, or a custom inset/liner, which fabricators such as ModernAire might sell. You can start with a standard design and build a cabinet around it, or start with a cabinet design and have the custom fabricator build an insert that snugly fits into it. If you are locked into a cabinet and a standard insert, then some sheet metal pieces may be needed to keep effluent from causing grease accumulation between the metal and the wood.

@kaseki - it is a metal hood, not wood, and it's an island install so cabinets don't matter. I'm leaning towards an external remote blower so I guess I just need a liner and the baffles/lights, not the fans and guts that are in an all-in-one insert? Right?

You seem quite knowledgeable on this topic as I've seen your name pop up in multiple other posts as well. Tell me, is it possible to use sound dampening foam to wrap the ducting in to minimize any noise it generates? I already plan to install a silencer in-line to help with this? What about with how the exterior blower unit is mounted? Can anything be done there that will help? (ours would be wall mounted, just above the roofline, about 8 ft from where the range hood goes up into the ceiling)

I'm sure in all of your research you have also learned that a hood with CFM of 1000-1500 will also likely require makeup air. Without it, you risk a dangerous backdraft issue.

I would share your fabricators shop drawings for the hood with Modern-Aire and or Prizer and ask them to propose an appropriate liner/insert. Give them as much info as you can about dimensions, remote blower, duct size etc. They should be able to give you what you need.

@Kristin Petro Interiors, Inc. Of course, why?

I must have misunderstood. I thought that you were installing a (metal of course) liner into a wood surround (generally called cabinetry), the whole of which might be called a hood for simplicity.

In any case, to answer your questions

(a) I use an automotive product for sound dampening made by [without running to the garage to check] Evercoat. It is a very heavy for its volume plastic sheet material used in automotive doors. It should be available at any auto parts dealer who supports the body shop trade. With 10-inch ducts, I use very long Ty-Wraps to supplement the material's sticky side to ensure that the material stays in place.

See also http://www.acoustiproducts.us/

(b) The down-slope roof blowers (I have one) are also used for down-wall blowers, and are normally hard mounted. I think it is helpful to ensure that it doesn't vibrate the structure it is mounted on, so some added support between rafters or studs (as applicable) may help stiffen the area. For extra fanatic points, you could take the blower fan blade assembly to a balancing shop and have it balanced. The large radial roof blowers tend to use cast blade structures probably not as well balanced as they might be.

I don't understand what wall above the roof line exactly means.

@kaseki Awesome, thanks for the detailed reply. I was looking at this line of products for sound dampening as well, looks promising: https://www.soundproofcow.com/soundproofing-101/how-to-soundproof-a-home-2/how-to-soundproof-hvac-systems/ 

I've worked a bit with acoustic panels for soundproofing music rooms so that's what got me thinking that if a lot of the noise is being carried by the ductwork, why not target that?

>I don't understand what wall above the roof line exactly means.

The kitchen is one story, the house it is attached to is 2 stories, so where the ducting will come out is on the wall just above the 1st story roof.

One final question if I may. I've read that in-line silencers can really cut down on the noise too (much like how a muffler in a car's exhaust works). I've asked a couple manufacturers about this but they don't formally have these (Wolf for example). Is there any reason I can't install one anyway though (like a Fantech one)?

I installed the Fantech 10-inch model. As far as I know, they were the original source of these devices. As expected, most of the high frequency blade tip turbulence noise from the blower, and similar turbulence noise from the duct on the roof side of the silencer were attenuated. Dominant noise in my system is hood baffle hiss, followed by some low frequency rumble due to not taking the effort to have my blower balanced (I think).

@kaseki thanks so much, very helpful. We need all this stuff in an FAQ!

@kaseki I did some measurements today, I have no room to fit the silencer in the ductwork near the fan (ceiling joists only provide about 12 inches and the silencer is 14 in diameter). Would there be any benefit to mounting it in the chimney part of the hood (this is an island hood so it could conceivably be attached directly to the liner on one end and the exit ducting on the other. I don't know if that would have any effect though...any idea?

The silencer can functionally be mounted anywhere between the blower and the hood. The closer to the hood the more duct turbulence noise is suppressed. I have an attic above my kitchen, so I just routed the duct in the attic quasi-horizontally to the blower and put the silencer into that space. Otherwise, one needs a duct path through a garage, or up an exterior chase, or (in extremis) through a second floor living space to get the needed space (diameter).

I should note that I have two kitchen vent blowers, the second one for ceiling registers above the wall ovens. This blower was originally (long ago) allocated to helping a LItton Cooking Center's pathetic vent path around its microwave oven. This (now 8-inch duct, I think, becoming forgetful) path also has a Fantech silencer on the way to its roof blower. This blower is a Nutone mini down-blast style and is fairly quiet. This second silencer is also in the attic.

kas

@kaseki - On silencers, I looked at the fantech silencers everyone likes here, unfortunately the 10" inch duct model is huge (14" outer diameter and 35 1/2" long) and I have no place in my install for this to be accommodated. I've searched for other models that might be shorter that would work but nothing, this model seems to be an industry standard size. So in the event I cannot find a compatible size, what steps can I take to limit the blower noise? They make acoustic wraps for ducting, mass loaded vinyl sheets, etc. It's an external blower that is wall mounted after about a 12-15ft duct run.

the first question is are these stock cabinets or totally custom cabinets. If stock the the hood will be a specific size and the liner and insert will have to meet these measurements. If custom or build to design then you can pick a liner and hood and have the cabinet maker make a hood exactly to fit. I have a remote blower on the roof so only the baffles inside need to be cleaned. The blower and motor are external. Your contractor, cabinet maker or manufacturer of cabinets should be able to guide you as to what you need to get .

The wrapping will help with vibration carried down the duct sheet metal, but not so much with acoustic noise carried down the air path.

The silencer has to be larger than the duct for the same reason that a car muffler has to be larger than its exhaust and tail pipes. The acoustic waves have to be partially delayed to mix with out-of-phase waves to cancel some of the sound, without adding significant pressure loss.

An alternative to the silencer for reducing blade tip turbulence is to operate the blower at a lower speed. For the same flow rate, this requires a blower that is larger in diameter than the usual manufacturer matches to desired flow rates. (Compare and or contrast a Casablanca type ceiling fan -- many CFM with no noise.) For kitchen ventilation, I would look into a commercial up-blast blower. These often have a belt drive between the fan part and the motor, and the belt sheave ratios can be changed for various purposes. So a, say, 2200 CFM rated blower operated with a sheaf ratio such that at full power the flow rate is actually only 1200 CFM, or whatever you need, should be considerably quieter than say a Broan 1200 CFM unit operated at full power.

There are many up-blast blowers available from commercial ventilation distributors, but determining what you need may be difficult. It would be for me without getting the necessary literature. You may find a source such as Greenheck to be willing to provide some advice over the telephone or someone at a local commercial HVAC outfit.

It is also possible (I've never looked into this) that Fantech could provide some low speed in-line blowers that together moved enough air and could be set to be lower in speed. This might be asked of their engineering support via telephone. But I would be surprised if they could do so without exceeding your duct diameter and still interface to the duct without pressure loss issues. Anyway, usually roof installations are easier to access than duct installations when the duct is nestled in the joist space and covered by gypsum.