Tankless Water Heater Venting through Attic

[Zande]

Tankless water heater to be in basement. Intake will be stubbed out sidewall and under porch. However, not preferred to run exhaust out same sidewall as it will need be ran up wall and above roof line (snaking around gutter). I have a closest chase that already has room in back and provide run from basement to attic (with an existing gas line already in it servicing A/C unit in attic).

So if I run a 3" exhaust vent up and out roof with suitable vent cap, any issue with water coming back into vent pipe and fooling tankless water heater?

Thanks,

 

[Bannerman]

You didn't specify which brand and model tankless unit you will be installing. I presume the vent material is to be PVC or CPVC which will be utilized with a high efficiency condensing tankless unit.

Each manufacturer will specify appropriate venting materials and configurations within the unit's installation manual.

For example, the Navien NPE Installation manual shows on page #42, the exact venting configuration you described. The Navien manual shows a PVC Tee to terminate the vertical PVC vent above the roof. Your unit's manual may specify an alternate termination method.

https://www.navieninc.com/products/npe-240a/downloads

There will be provision to drain water that may enter the vent stack since some moisture condensation will typically form from the warm gases being exhausted through the pipe. The bottom of the exhaust vent is to be plumbed through a trap to discharge to either a home drain or to a condensate pump.

 

[Sponsor]

 

[Zande]

Thanks.

It is a Navien 240a and this is also the literature I have been referencing. So it sounds like the condensate drain takes care of this anyway if it where to collect moisture.