Advise on in-wall Toto install

[TheGewp]

I am leaning towards a Toto AP wall-hung and carrier and it will be up against an exterior 2x4 wall. I plan to butt a second 2x4 wall up against the existing so the tank is not against the siding, but i'm wondering if i should leave the drywall on the existing wall or not. I like the idea of an additional barrier, even though i lose an extra 1/2". Are there any down sides to it?

Also, my main concern about the in-wall tank is having to tear the wall about if there is an issue. Does anyone know how long these tanks generally last? Thanks!

 

[ss3964spd]

The drywall isn't adding any meaningful R value, so you'd be better off with removing the drywall and adding 1/2" foam panels.

If I were doing this I'd strip the wall to the studs and remove the existing insulation - which may not have been installed very well in the first place. I'd then caulk the inside perimeter of each stud bay where the exterior sheathing meets the studs, and check for/seal any holes in the top and bottom plates - thus eliminating or greatly reducing air movement in the stud bays. Install new insulation, carefully fitted. Install 1/2" insulating foam panels, but if the insulation you installed is paper faced be sure to defeat it by slitting it many times in order to avoid a moisture "sandwich" between the face of the paper and the back of the foam panels. Then build the 2nd wall against it.

The carrier tank should last longer than you. All the other "guts" are accessible from the front through the flush plate opening.