PVC vent pipe routing conundrum (pitch) for tankless water heater

[kwhubby]

Hello,
First time poster, Long time lurker on this forum.

In my crawlspace, I've replaced my old tankless water heater with a high efficiency tankless water heater (Navien NPE-240a).

For the exhaust I was assuming I would run another PVC line horizontally along the high efficiency furnace exhaust. HOWEVER, the furnace exhaust starts near the ground, while the tankless water heater exhaust is above the unit near the ceiling. This means I can't pitch the exhaust upwards for the same horizontal run. The space is highly congested with ductwork, so I have limited horizontal options.

I have three ideas, I wonder which I should approach:
1. Run the PVC vent DOWN from the unit to reach a lower starting elevation, and figure out some kind of mid-line condensate trap,
Is there an accepted way to create a mid-line condensate trap (2" reducing T to a P trap?)
2. Run the PVC vent in a different direction with proper upward pitch for ~10ft until it's blocked by the ceiling, and then angle it downwards for the remaining 10ft to the wall. I'm not looking forward to puddles of water outside with this.
3. Put PVC in the old straight 6" vertical chase to run the vent out the roof. I'm not sure how I would terminate at the B vent cap. Asphalt shingle roof, I've added some flashing before, I could begrudgingly replace it.



Thanks!

 

[Jeff H Young]

up and out roof 3rd choice . If flashing the vent is the only issue its usually easy on asphalt shingle

 

[Sponsor]

 

[John Gayewski]

You cap the old vent and drill a hole in the cap for your pvc, then use a metal roof boot.

 

[John Gayewski]

When doing a cascade system the exhaust runs downhill not uphill. If your can see in the picture there's a tee at the end with a pigtailed tube. I would call Navien and ask if this is permissable with a single unit, but only if I needed to. In my opinion straight up and out is gonna be your best bet.

 

[Jeff H Young]

You cap the old vent and drill a hole in the cap for your pvc, then use a metal roof boot.

even a storm collar might work but flashing a vent is no challenge as John points out.

 

[royalflush001]

The 3rd option could provide a clear and efficient venting path, but it might require more complex installation work involving flashing and roof penetration. If you have experience with roofing work and are comfortable with replacing flashing, this could be a viable solution.

 

[Jeff H Young]

I think the first 2 options he mentioned involved the best paths he could find but Maybe look a little harder. Id need a reason not to proceed up through the existing hole . he could very well have one I just havent heard his answer on why not

 

[kwhubby]

Thanks for the help! I think I will pursue option 3.
The only reason I wanted to avoid 3 was for ease of installation and to keep things consistent with the adjacent furnace. I also had a crazy idea to hang a mosquito trap near the exhaust (CO2 attracts them).

I'll have to cut and joint 5ft segments to fit up through the old opening from the crawlspace, and disassemble some of the B vent to deal with a 45 degree turn in the attic.