Plumbing Remodel Help

I've asked my plumber about this but before I call him back and waste his time, I wanted to see what the Hivemind said:

I want to move my toilet about 40" away from it's current position, but utilize the existing vent and vent-to-main connection. Why? My home's main drain is deep under my slab, which includes hydronic lines. My current plan avoids disturbing any hydronic lines because for some reason there are none in this area where I plan to add the toilet flange.  

The existing toilet flange will be swapped with a shower trap, and become a shower drain. 

My concern is the tie-in point between the existing toilet drain and the new toilet run. It will be at a 45º angle only inches from the vent stack. 

Is that allowable per code? I could've sworn my plumber said "no problem" but just wanted to check with others. 

The problem I see with that is that it's not a 45d angle, it a 135d angle.

You're asking the waste to make a very acute angle.  Combined with the low-volume flush toilet, I see lots of future clogs.

You're also tying in upstream of the future shower drain, which also doesn't fill me with confidence.

I would mirror the exit angle of the new toilet sanitary piping and come in at an angle that is both obtuse and downstream of the shower drain.

I'm sorry I'm not following.

The toilet drain is downstream of the shower. The vent is "down". The shower drain run towards the wall, past the tee with the toilet pipe, to the vent, then back under itself to the main drain. Does that make sense?

EDIT: this actually make me wonder if I have the routing correct in my head. If the vent is upstream of the toilet, which it probably should be, that'll change my plan a bit. 

I see problems.

First the current toilet drain does not have a "P" trap.  The shower will need one.

The angle you've drawn for toilet waste to travel is not good.  (as pointed out above)

I'd be cutting up the floor and plumbing it correct... but your hydronic lines may make that expensive.

pheller said:

I'm sorry I'm not following.

The toilet drain is downstream of the shower. The vent is "down". The shower drain run towards the wall, past the tee with the toilet pipe, to the vent, then back under itself to the main drain. Does that make sense?

EDIT: this actually make me wonder if I have the routing correct in my head. If the vent is upstream of the toilet, which it probably should be, that'll change my plan a bit. 

You're showing the "main drain" dashed in to the left of the shower.  If that is your sanitary main, the toilet as shown is routed at an acute angle over near the wall, whereupon it has to make a roughly 120d bend to head back toward the old location (new shower).  It also joins the sanitary upstream of the shower.  If you take the toilet plumbing from the new location at the same angle - except to the left instead of right - you will be joining the sanitary lateral downstream from the old toilet location and at a shallower angle.

Unless I am misunderstanding your drawing, which is of course possible.

Rule on venting is twice the pipe diameter plus 2.  So a 1.5" pipe is 2X1.5=3, plus 2 equals 5.  So 5 feet max before vent is pulled off.  2" pipe is 6 feet, 3" pipe is 8 feet, and a 4" pipe is 10 feet.  Vent needs to be at least half the pipe diameter but no less than 1.25".  No plumbers use 1.25" pipe, so minimum vent pipe is always 1.5"  Any pipe(DWV) underground has to be at least 2".  But you have a lot more going on then simply trying to find max distance for a vent. 

So I've begun to dig into this some more. 

1) Toilet does in fact drain towards the wall and meeting the vent pipe at a 90º angle. 

2) I've already hit and repaired (temporarily) a hydronic line. It's all fair game now. 

3) Now I'm trying to decide on the order in which to hook this all up. See pic: