I thought about going straight up with it, but I don't have a lot of room due to the angle of the ceiling. Plus, I am going to be using a canopy style hood, so the chase would have to be rather large to be in proportion with the hood, and I'm not sure how that would look. I did think about placing cabinets on top and then a chase above that, but again I am probably too close to the rafters in the attic due to the slope of the ceiling. Consequently, out the wall and into the garage attic seems to be the simplest way to go. Plus, that gets the inline fan away from the house and makes everything more accessible. I don't mind enclosing the vent in drywall to bring it up to code. While the vent needs to be in a soffit, what about the inline blower? It seems like the blower should be left out in the open, with the remainder of the duct enclosed? That said, I can see what you are saying about direct penetrations from the garage into the house are not permitted due to fire concerns. However, would a solid duct running from the kitchen into the garage attic and out the roof fall within that logic? There are no breaks in such a duct run, since the only openings are at the hood itself and wall/roof cap. So as long as the penetration where the duct goes from kitchen to garage is sealed with fire caulking around the duct, how is there an issue? Again, I don't mind enclosing the duct run in a chase if need be, but it seems like overkill....

If your hood is on an outside wall, your not going to want to protrude through the roof too close to an overhang, especially if you are in cold country with ice dam concerns.You would have to elbow up to a higher location.In our area,a fire stop is required where the ducting enters the cieling/attic with any framing required to be 2" away from the duct.A fire stop is a sheet metal jack that accepts the ducting in the center.The fire stop is attached in your attic to cieling joists or blocking or both.The fire stop isn't so much for heat,as hoods aren't high heat,but are required to slow fire through penetrations.Your roof sheathing should be cut 2" larger than the ducting as well. The roof jack will easily cover that. A t-top roof jack is simply a jack that has a horizontal "hood" that keeps water out of the jack/ducting. You are going to want to study how other vents on your roof were flashed as well concerning your roofing, as an improper flashed jack is a guaranteed leak.If you use foil tape on the seams of your ducting,(my choice), make sure it is rated for heat.Good luck on your project! You might want to check in with your local yocals for venting requirements in your area. That's what they are there for and is a safer bet.

I'd like to add my (civil) 2 cents: TexasCatherder has a good question, and there are many right answers here. - Do you "need" a kitchen range vent? Yes, in most jurisdictions using international building code, some kind of kitchen ventilation is required. If you don't want it, don't put it in. But it may haunt you upon inspection at resale of the home. - No, few jurisdictions require a big ole' "range hood" over the range. In my community, it just needs to be some kind of vent that can circulate the right number of CFMs for the space. For example, a friend recently renovated her kitchen; she didn't want a big hood over her range in the island; and according to code, she went with a small wall-vent on the other side of the room on an exterior wall. That's enough for the "needs" of code. - But yes, like many have noted, a range hood does a better job of capturing grease and moisture than a wall vent. I'll bet my friend's lovely white kitchen wall gets a grimy film around that wall vent in a year or so. - Besides grease and water vapor, yes, gas-fueled heat sources produce toxins. It's not enough to kill or annoy most people, but the cumulative effects of the toxins isn't good, and those who are sensitive to allergies may suffer, and it's generally not a good idea to burn stuff (including chicken or toast) without ventilation. - Ventilation is important for indoor air quality and the structural integrity of the home. One thing that we recently became aware of is the need for ventilation just to get rid of moisture. If you have a well-sealed and insulated home, every-day water vapor from cooking, cleaning, bathrooms, laundry, etc. can build up and not escape the house. It can cause condensation inside walls and windows, which can lead to mold, which is a major indoor air quality issue in our part of the country. Additionally, although it doesn't seem logical at first, it can lead to structural problems. Air in a home circulates from colder regions to warmer regions, and the moist air goes with it. There's a photo in a an old-house-renovation book we have that shows rotting roof rafters in an attic: Rotting not from a leaky roof, but because of long-term water standing in a basement and crawl-space! It was three floors away -- how could that be? Air circulation moves the moisture up. - Anyhow, it sounds like our dear OP TexasCatherder got the point that ventilation is important. So maybe we can help her now focus on where to put it? Rather than debating the pros and cons of ventilation, perhaps we could start a new thread to help her with layout? She's going to have a beautiful kitchen, and folks here are great at taking the cook's priorities and giving suggestions for layout to help reach those goals.

I understand it's pretty easy. And required by law in some jurisdictions (like ours). Who installed the ventilation system? I think that's a pretty big booboo, though apparently done all the time. I think if you mention it to the installer they'll do a gratifying two-hands-over-mouth, wide-eyed "oops", be so red with embarrassment they'll fall over themselves getting over there fast enough to fix it. Could be wrong of course, but I do think this is like forgetting to put oil in the car after an oil change ... well, maybe that's a bad analogy; your house won't blow up. But it's really not the done thing though forgotten distressingly often enough. Just call and mention it. Even if they want to charge you something really, they should have known to have installed it so they ought to give you a substantial price break. It was the professional's job to tell you about it. IMO. ....on second thought I imagine the difficulty might depend on how much stuff is between the hood and the cap; springs and braces, etc. Regardless, you need to do it. Let the installer make excuses....