Consider yourself ridiculed since you didn't put your ducks in a row before starting the project..

Thanks for no information whatsoever. If I read between the lines, I'll have to rip out the ceiling. I can afford to do so - I just don't want to. I also don't want a crappy all-in-one range so this was inevitable - whenever the ducks decided to line up. So if I have to rip out my ceiling and have it redone, so be it. At least my kitchen will be worthy of the word - and not what the builder thought was adequate.

First, the height of the space between the floor joists above the kitchen ceiling needs to be 14", or so to allow for 12" ducting and clearance. Most floor joists are 2" by 10" or 2" by 12", both of which do not create the necessary space, The space created by 2by12 lumber is only 11 and 1/4" high. If the joists are set on 16" centers, the width of a cavity is 14 and 1/2" wide.

Round ducting cannot fit so rectangular ducting will be the only option. That means the necessary area will be close to that of the round ducting if the ducting is 14" by 11". If the joists are 2" by 10", that height is down to 9&1/4" and the necessary area is too small.

So, yes, the ceiling gets cut as a minimum. However, given the space requirements for the 12" recommended ducting, it seems probable you will need to do some extensive reworking. Maybe create the chase(framing around ducting) which will protrude down from the ceiling for the distance from the stove to the outside wall.

The above is an educated guess, since I am not an HVAC person, but have some experience in planning and building.

If you can fit a 8x14 square duct that will give you about the same area as a 12" round (112 in^2), so you should be good, if I've done the math correctly.

Cutting out the ceiling is not a big deal, just cut on the joists so you have something to screw the replacement blueboard or drywall into. Tape the edges and skimcoat the whole span. If you want it to look perfect you'll need to feather the plaster out by 12-18" on each side of the taped joint. If you hire a pro to do it in our neighborhood I'd expect the cost to patch the ceiling with blueboard and plaster to be $350-500. You're lucky it isn't textured, matching existing texture is a pain, and takes a really competent plasterer.

You will be very happy that you've opted for good ventilation, it is well worth the cost and effort.

How many cfm is your fan? My 1260 cfm fan requires a 10" pipe. I thought that that pipe was big. 12" would be a monster.

We installed a similar vent-a-hood (48" with 900 cfm triple blower fan), and you will definitely need to do some work on your ceiling. We installed in a 1 story house, and we were using the vent-a-hood liner, not the stand-alone housing. They built a decorative plenum above the range (cathedral ceiling) and recessed the hood liner up into the plenum. The ducting then connected straight up to a vent through the attic and to the roof.

I believe that the unit you picked is actually two 600 cfm dual fans that each require an 8 inch duct. You can then use a duct combiner (about 17" tall) to bring them together into a single 12" duct. The centerline of each 8" duct is about 11" away from the centerline of the hood.

Do you plan to build any type of decorative plenum/trim above the hood to get the hood to the correct height over the range? If so, that could give you some working room for ducting options. The option I am considering is whether you could use two 8" ducts, but jog one over so you could run them between two adjacent floor joists or one above the other (hidden by a plenum). It still requires removing quite a bit of ceiling, but will fit well with typical joist spacing. The other choice is to run each 8" duct a different direction along the joist, but you will probably run into a load bearing wall in one of the directions.

The other option is to look at the floor above to see if you could route the 12" duct (or two 8" ducts) vertically. If you could grab space from a closet or the corner of a room, you could run the duct(s) straight up and out the roof.

The code requirement for make-up air when a fan moves more than 450 cfm is a relatively new requirement. If your city follows code, you will have an added expense for an automatic make-up air vent that opens when you run the exhaust. However, I installed a 600 cfm fan during renovation of my current house in 2014 and the inspector never even mentioned make-up air, so YMMV.

Removing and replacing sheetrock ceilings is messy, and looks bad when its out, but its really very straightforward construction work that does not require a licensed professional. I would not get very concerned about how much ceiling has to come out.

Bruce

HandyMac, Rwiegand - spacing seems is adequate for rectangular ducting (2 x 12 joists). If it wasn't, I could move the range + hood to the other side of the kitchen (outside wall) - was hesitant to do that because it could be viewed from the formal dining room (and who wants their guests to see the mess that made the meal?). Thanks for reminding me how hard it is to patch textured ceilings - had them in a former condo and just changing light fixtures left ugly patches. We are installing additional recessed lighting - so the ceiling will be cut up anyway (decision made recently).

Sophie - We have a HRV already but it may be too small (I really don't know the Ontario Building Code very well) - only 77 cfm continuous ventilation for a 2600 square foot by 9-10 foot ceilings (tiny Toronto home) - but have space in mechanical room for an upgrade if necessary.

Bruce - only load-bearing wall is the exterior wall. Toronto homes are usually one room wide! I'll let my builder make the final decision regarding vent size/shape but you raise an option that sounds plausible to me! We have the stainless going to the ceiling so no trim, by the way. Our kitchen will have modern stainless for appliances and fixtures - and rustic American colonial cabinets on the working side and American Federal cabinets of the storage side and island.

As for CFM size of this hood - it was best choice re price and width for us. Deep fryer must be 15" from gas cooktop - and both need venting. We're venting a 15" area of countertop but two hoods would look ever so stupid.

Thanks everyone - I now have an image in my head about what's needed and what it will look like through the process.

Here are some ideas you might try to repair the ceiling texture:

Sprayer

Roll on texture

Several years ago, I used a kit with two rollers to apply the texture. I had to cover everything under the area(application is messy) and was able to make almost seamless repairs on sections where the sheet rock was cut out and new sheet rock installed. In most cases, I also repainted the entire ceiling with ceiling white.

"As for CFM size of this hood - it was best choice re price and width for us. Deep fryer must be 15" from gas cooktop - and both need venting. We're venting a 15" area of countertop but two hoods would look ever so stupid."

You might want to explore this a little bit. The cfm of the hood dictates the size of the exhaust pipe. Perhaps you dont actually need a 12" pipe. bcarlson says that your unit is two 600 cfm units where the ducts come together in a junction where two 8" pipes are brought into one 12" pipe. Maybe you could avoid that 12" pipe by selecting a blower that is not 2 separate units? My 1260 cfm unit only requires a 10" pipe. That could make a world of difference in terms of what you have to do to get that pipe to the exterior of your home.

As an aside, I have been very disappointed in the level of knowledge about these issues from my local brick and mortar appliance retailers. One guy was ready to sell us $7K worth of cook top and range hood and was unfamiliar with the concept of make up air. Not that he was not qualified to compute what was needed. He clearly had no idea that forcing 1250 cfm of air out of the house required that 1250 cfm of air come in to the house to make that up.

Good luck!

Found a Fantech system that will augment current HVAC for a reasonable price ($4000 plus installation) - what's another hole in the wall? There are already plenty - and if you saw what they did with our upgraded electrical box, you'd fall over laughing - safe but they pretty much just ripped a hole in the wall and shoved a bigger pvc pipe through with the rough electrical - didn't refinish the wall - built a 48" x 54" x 6" barn - or dart board box - around it - we're going to have to pay a few thousand for that mess - it's in the open - by the back door! Open the barn door and all you see is particle board and wires around the panel. UGLY). 1600 cfms - and probably the Builder should have thought about air exchange when we asked for gas connections in the kitchen and laundry room - with 4 bath fans, gas dryer, and current hood we're probably pushing it right now! Seems when you buy even a new build, you have to answer your own questions - thanks everyone for helping me answer mine.