jill: 1/ it sounds to me like this will work, since the window is high enough. 2/ There being a big window in the wall, don't worry a lot about what is "possible structurally under a load-bearing exterior 4" wall" because someone before you has already done the work to get whatever structural reinforcing was necessary to allow the window in the first place. The question is best when reworded: the window have already been "framed" and you want to put some thingie between studs, under the window. A plumbing forum is not the place to ask this. When you open the wall, underneath the window you will see studs but know this: they are not the studs that hold the building up; they happen to be the same size and spacing as all the other studs everywhere else, but this was done in order to remain standardized, not to hold the roof up. Of course you may wish to have all this confirmed by a couple other people including real on-site visitors. The remodeling forum might be a good place to go to. 3/ To put a wall carrier under the window might mean that you move a stud over by an inch or two. No big deal, not at all. Under the window you could also replace them with smaller ones and have more room for some continuous insulation (because you want to reduce air, wind, cold from coming in). Take this to the remodeling forum. - Plumbing. The drain pipe "angle" is also no big deal. One day you can post again with a link to a photo on the internet, to get tips where to cut and which fitting to buy to connect to the drain. One of the numerous advantages of a wall hung toilet with an in-wall carrier is that you can have a vented drain instead of a long S trap drain. (b.t.w., all toilets are designed to work on S trap drain configurations, so it will be OK either way, i.e. with or without a real vent or an AAV vent.) The toilet wall carrier has a drain : you could connect it to a vented drain line (e.g. using a real vent or an AAV (search "AAV").) Just one thing to know. Good to know. When it comes time to connect the carrier, you could remind the plumber of this. About the elongated bowl: people get used to the bowl size they use all the time, so I would urge you not give in to the impluse to try to find the largest bowl possible. Any reasonable size bowl will be fine, if it's larger than the toilet you currently have. Hth

When you install a wall hung toilet you are remodeling in a bigger way than if you just replace a floor-mount toilet bowl. What to Do about The hole: - you can remove it. This is work. - you can use the same drain for the new toilet, if this improves your layout. This is also work. Doing so works well with new venting from above, but it also works unvented, because toilets are designed to be generally unvented. Wallmount toilets and rear mount toilets have the advantage of being able to have their drains be vented before going down under the floor. The Geberit drain can be oriented left or right (sideways) to pick up a vented drain. Or they can be oriented to go straight downhill. Hth

Thanks for the responses. Look like I can't use the Geberit as my wall is 2 x 4 build, and there is no room to use 2 x 6. I'm not sure if having the tank inside the wall will be a maintenance issue. Probably a really dumb question... but I assume you would have to tear the wall apart if you ever needed to repair/replace the tank and associated parts? I'm somewhat hooked on a cabinet vanity. To me, pedestal sinks are not very useful... small bathrooms need all the storage space they need and pedestals don't offer any. But thanks for the links. I do like the design... I do have a primitive drawing but don't know how to upload to this forum. I have a CAD drawing but I've made so many changes to the original (which was approved by the city for permitting) that it would be misleading. The reason why I think a shallow 48" would be nice is that I can run it the entire length of the bathroom up to the shower partition... which I would like to tile up to about 40" or a few inches above where the vanity would end, and then glass up to 8" shy of the ceiling. From the shower partition, the shower is about 32" x 66". So it works well in the 7' x 5' 6" square box. Also, going with a long 48" vanity allows me to go really shallow. A very shallow sink/countertop is not as bad if it can be stretched out across a wider area. Total countertop/sink space is what I think people are most concerned with. I might try to find a really shallow sink/vanity... around 14" perhaps. Do you guys think 14" is too shallow for a sink vanity? This would allow me to go with a more standard toilet (round bowl) that hopefully offers dual/flush options. This is an urban zero-energy/smart home with water catchment so I need to go with the most water-sensitive models. I'm hoping to find a model that has a tall tank that will be a little tighter to the wall, now that I know an in-wall tank (e.g. Geberit) won't work. If I can find a nice 26" toilet and a 15" vanity, that will leave 25" of clearance between the vanity and the toilet... and I think this is reasonable. Oh, and the Neorest is very nice... but I'd like to keep my toilet expenditure in the $500-$1,000/each range. I actually need 4 shallow toilets for the project so I have to be a bit more sensitive to the price.

Now that our installation is complete, i thought I'd answer my own question in case anyone else is interested. We used the Geberit Sigma tank designed for 2 x 4 installations. We wanted to go straight down, not the angled option it allows which they indicate does require more depth. But even the straight down option still did not quite work in a 2 x 4 framed wall and we had to shim out the wall a little bit. Not a big deal for us, but just a heads up. In addition, Geberit has a Sigma tank for 2 x 6 walls and an Omega tank for 2 x 6 walls that is designed for half walls and so the frame is not as high. The Omega tank does allow for the flush plate to be mounted either on the front wall or on top of the wall - the Sigma models do not have that option. I am looking at the Omega option for my next bathroom remodel because I want a ledge behind the toilet and don't want the ledge too high. I do note however, that the access area (through the flush plate opening) is smaller than on the other tanks. Not sure if this will be a big deal or not and if anyone has any experience with the Omega model please comment. By the way, we love our wall mounted toilet. Definitely more expensive and difficult to install, but worth it IMO.