As long as both the blower and duct size are correct. You could do internal blower or in your case you could do an in-line blower in the addict and reduce noise level and increase effect.

There is a significant loss in exhausting power for every turn the vent makes, and a 90 degree turn has to be made GRADUALLY, never a tight turn. The shortest run possible is always best, all other things being equal.

We installed a Broan hood 14 years ago that vents straight up through the attic with the fan motor placed in the attic just within the wall where the vent exhausts to the outside. The system is a bit outdated by current standards, but has worked very well. The remote fan location really cuts down on the noise. We're thinking of updating with a new Broan, one of their "Best" product line. But there are others out there that may be as good if not better.

While it is true that long runs and 90-degree turns decease efficiency, it is also true that a system can be designed to correct for those losses. I was in a situation very similar to yours. I chose not to punch one more hole through my roof. My experience has been that any time you cut a hole in a roof it is a matter of when, not if, it will leak. I needed to go to 10" ducting and a larger blower, but it was worth it to me. I found the technical support staff at Prestige very helpful in specifying a system that would work for me.

Thank you for the responses.

It's going to have to go through the roof at some point. What's the difference if it goes straight up or runs along until it goes through at the peak? You're not talking putting the exit in the vent at the peak, are you? Your attic won't have adequate ventilation if a gable vent is compromised. That vent has a purpose and is already sized for that purpose and cannot be downsized by having a 10" duct running through the middle.

It'll be a lot costlier to engineer a complex run, and you'll have to upsize the vent piping and the blower. Roof penetrations DO NOT LEAK if they are properly done. Any that leak, have improper flashing and sealing.

You're not talking putting the exit in the vent at the peak, are you? Yes I was.

Or maybe I didn't understand the question right. We will install the vent hood above the stove and have duct going from that to the attic, then will take a wide turn to do ductwork all the way to the peak. Duct would be exit at the peak. The only fan is the one in the hood in the kitchen.

If your house's attic has a ridge vent or you ever plan to switch from pot or gable vents (or whatever it has now) to a ridge vent, you should put the exit somewhere other than at the peak. Doing so may also allow you to shorten the run.

We will also be exhausting our Best by Broan hood (either K260A or WP29) through the garage attic, using an in-line blower (probably 1100 CFM). We could have gone through the wall but decided not to for cosmetic reasons and because going through the roof will be easier and cheaper than going through masonry.

The vent has to go through the roof at some point. Period. It cannot run through a gable vent (Vent on side of house at the top where the two flat sections of roof form the peak). It can either go through the roof straight up, or, for aesthetic reasons, can be ducted over slightly (For instance so the vent protrusion is on the rear of the roof rather than the front face). Your gable vents are sized so that your attic receives proper ventilation and remains at ambient temperature. Decreasing the attic ventilation by running a 10" vent through the gable vent will result in higher attic temperatures during summer (higher utility bills for you), shorter lifespan of your shingles, and a warmer than needed attic during winter leading to possible ice dams that will damage your roof.

it would run out to the peak but need to cut a hole there on the side of the garage.

"The vent has to go through the roof at some point. Period."

I don't understand this statement. We had a side wall mounted centrifugal blower exhausting a commercial hood for 18 years and it seemed to work just fine.

I agree that a proper installation will not leak, although the flashing will have to be checked periodically because it is not likely to last as long as the roof. I would also avoid exiting at the peak. It seems like the most complicated way to go. Can you make the duct turn slightly so that it ends near but not directly on the peak?

i do not have a gable vent on the garage side.

GO straight through the roof and have a real HVAC person do it. It'll be engineered properly and the roof penetration will be properly sealed. And, it'll be cheaper and more effective.

HVAC?

Heating
Ventilation
Air
Conditioning

In other words, a professional.