Range hoods are complicated. One rule of thumb that may apply in you decision is borrowed from HVAC, minimize 90 degree turns. 45 degree turns are acceptable. So, plan on whichever pathway gives you either a straight shot out or can be planned using 45's.

You may need make up air (MUA) depending on where you live. The farther north, the more likely.

Whether you need makeup air or not has nothing to do with where you live, it has to do with how powerful your hood is, how tight your house is, and what gas appliances you have.

Whether you need heated makeup air depends on where you live.

Thanks for the info, guys!

First, regarding Make-up Air: Where we are building in British Columbia, the code requirement is that if there are other non direct-vented gas appliances in the home, MUA is a requirement, otherwise it is not mandated by code. As hvtech pointed out, if we were to supply MUA, code does mandate that it should be heated. That puts us in a bit of a tight spot, as I am aiming for below 1.5 ACH50 on our blower door test, which is a fairly tight house, and all of our heating/cooling will be radiant based - no ducts or furnace to tie MUA into.

Kaseki - thank you for the detailed information! I realize that I won't be getting no noise at all (although this is new construction so I can make reasonable accommodation ot minimize noise). From my understanding of your comments, if I have an in-line blower installed in the attic before venting out the roof, and the kitchen is on the ground floor, a silencer somewhere in-between would not do anything to reduce noise in the kitchen itself, correct? It would be more for the purpose of reducing noise between the silencer and the blower?

From the responses so far, it sounds as though my best bet would be the ~25' run straight up and out the roof, as far as noise goes, right?

Thanks!

Sorry if I was unclear, but the silencer removes noise that is beyond the silencer relative to the listener. So, not that it would matter, but hood baffle noise would be partially silenced when listening on the roof.

Relative to the cook in the kitchen, the silencer removes noise beyond it. So, hood baffle noise and local duct noise and local hood interior transition noise won't be affected by the silencer when listening at the cooktop, but duct noise on the roof side of the silencer and most importantly blade tip turbulence noise from the roof blower or the in-line blower that is past the silencer (relative to the hood) will be attenuated when listening at the cooktop. The blower noise is typically the loudest, so the silencer is important to minimizing noise.

(It is worth pointing out as I think I did sometime in the past that blade tip turbulence noise dominates baffle noise given well designed baffles. I only have personal experience with my Wolf/Independent hood, so it is possible that a particular baffle design could be noisier than a particular blower design.)

So the silencer should be as near as feasible to the hood (past any dampers), and the motor closer to the roof or on the roof.

A duct that passes heated rooms should be insulated from the rooms passed, and possibly partially coated with damping material (I use automotive sheet metal dampener sheets).

A damper is needed at the hood (probably part of the hood) and another should be at the roof. The Wolf/Broan low profile blower I have has its own damper which opens upon flow. Abbaka and Broan blowers look similar and appear to use the same approach. An upblast or downblast quasi-commercial blower and housing design may need a conventional damper just below it.

Dampers should be checked for function without hanging up on errant screws before workmen can escape the project.

A straight run will have minimal duct bend turbulence noise (caused by flow separation, perhaps). It may or may not make adding a silencer inconvenient, architecturally.

kas

Kas - that was super helpful, thanks a ton! I think you have pretty well summed up everything I needed to know in your two posts. Now I just have to choose which hood to go with, though that is a topic of many, many existing threads already. (Zephyr seems like a nice choice for quiet, but not for the pocketbook)

Camembaron:

My hood and vent system, not even including my under-construction self-balancing MUA system, cost far more than the induction cooktop plus induction wok under it. Maybe throwing in the wall ovens' cost would make the venting system cost secondary, but the ovens aren't directly handled by the hood and have a separate quasi-useful vent system.

I think this relationship could also be true of commercial kitchens. Certainly their ventilation operating costs dominate their cost of business.

Good luck with your project.

kas

When I purchased my exhaust hood the installation manual gave the specifics of air flow and loss each duct component reduced the flow. The size of mine was 8 inch and the duct was limited to 100 feet. An example a 90 degree elbow is rated at 17 feet from the provided chart. You can find information at GEAPPLIANCES.com including MUA which may be useful

@kaseki If you're still reading, are you aware of a duct silencer that is 18" long? The shortest I can find is 24" and I don't have room for that. But from your excellent explanation, it seems if I use an external blower then maybe I don't need a duct silencer.

In principle, if Fantech made a silencer half as long as a present model, the low frequency cut-off might be expected to double. The resulting annoyance impact is unclear to me, and likely depends on the acoustic spectrum of the blower. I am not aware of 18-inch silencers for reasonable hood sized round ducts. I did run across a source of internal rectangular duct products that I mentioned to a forum member once, but I don't seem to have kept the link. These were shorter, I think. I recommend searching on 'duct silencing' and 'duct silencer' to see what might be out there.

The threshold of "need" versus "nice to have" is hard to define, and clearly individual dependent. A distant roof blower will appear quieter at the cook than one only two feet from the hood, but might still be too loud for comfort.

Another approach given adequate duct diameter is to use an oversized blower and operate it at partial power. This slows the blades, greatly decreases blade tip turbulence as well as noise from duct turbulence, and generally proves to be quieter at the cooktop.

However, in various circumstances the MUA maximum flow will have to be designed to match that of the oversized blower, so some cost inconvenience will arise.