Wondering if this venting configuration is OK or if there could be an issue with a larger WH unit upstream of a smaller one? This is in an unfinished attic.
There are other issues there, but im just wondering if the venting is all good
No, the venting is not good. The single wall pipe in the attic would be enough to refer it out let alone the lack of supports, eh?
Did you fire them both up and check for backdrafting? 
From what I can see, Ken was telling Smith it was getting hot in there and to take his jacket off, and looks like they both agreed. :mrgreen:
LOL :D:mrgreen:
I didn’t fire them up - it was an occupied two flat.
Your right- there already was some other goodies, leaking gas valve, possible asbestos insulated pipes ( could be combined with cloth covered insulation) Not to mention they were not wearing their coats. Both units have that plastic TPS discharge pipe.
The single wall doesn’t touch any wood or combustibles though.
I was considering if the set up would allow for back drafting.
Single wall pipes need 6" of clearance. Taped pipes are not acceptable, needs mechanical connections(ie screws). Check for back drafting at the top or the water heater with a mirror(condensation).
Now if you found all that other stuff, they need a specialist anyway. 
Looks like inadequate rise/run for a naturally drafted appliance too.
That is kind of what i was thinking but was looking for an echo.
The whole building was full of home owner DIY SHORTCUTS
That should also be a Y connection Joe.(did someone mention hangers?)
The gray panels in the background may be asbestos transite too.
The main pipe must be equal to the largest connector +50% of the others.
anyone have the code for rise on exhaust?
M1803.3 of the IRC
[FONT=ArialMT]The horizontal vent run
[/FONT][FONT=Arial-BoldMT]must be pitched down toward the terminal end[/FONT]
[FONT=ArialMT]1/4” per foot for condensate drainage. The slope applies to the entire length of
the horizontal vent run. Failure to pitch the vent run properly may damage the
heater due to condensate running back into the unit.
Use non-combustible supports on vent pipe. Support lateral runs every six feet
(1.8M). Support vertical runs of Type B double-wall vent pipe in accordance
with the requirements of the pipe manufacturer. Support lateral single-wall pipe
in accordance with accepted industry practices. Do not rely on the heater for
support of either horizontal or vertical vent pipe.
[/FONT]
Were the CO levels checked??
Should be, but that does not always show properly and this is in the attic where hopefully one finds circulation.
Needs to be re piped anyway.
First of all I think everyone can agree that this is a “hack” job to begin with…Joe… Refer out for evaluation by a licensed qualified plumber…
Second If this is in Chicago, It has to follow some basics on installation… Our “code” is clear as mud… All installation within attics are NOT allowed with new installations BUT they can be in attics IF they follow 18-29-502-6 BUT
the venting is NOT the best yet single pipe is allowed in attics…YES per Peoples Gas… Now the slope connections and such…well that is a hack job…
The problems… Combustion air? Flooring? Solid or just a sheet under the W/H// Access? Sizing… TPR extension is WRONG if it is PVC… How about CPVC??.. Drain at the floor? Drip pan? Can’t have the TPR drain in the pan… Yes it’s that confusing… How about the location of these appliances… What do you think the combined weight is… Over the living room ceiling or bedroom…
NOT allow per City Code… How is that for confusing…
Yeah, there were vents just to the right and left. At least ventilation was good.
The pipes may be covered in asbestos insulation at some sections.
This will be very hard to see in the pic, but the " roofer" installed composition shingles over the existing wood shingles 
It was a 1918 two flat.
So, they are just venting sewer gas into the Attic?? Nice
That way the birds nesting in the waste stack aren’t subject to the sewer gas. 