navien tankless intake air piping

[ratsandtats]

i work in maintenance. our 8 unit navien tankless water heaters have a 10 inch air intake that i need to extend 3 - 5 feet as the original installer placed it at the top of an 8 foot pit with dryer exhaust coming from the bottom. the goal is to give the units more fresh air than they are currently getting to get a cleaner burn. the current plan (not mine) is to use a 10 inch straight fernco and just add a length of pipe.

 

[breplum]

It is fine to use a rubber or glue coupling. However, be sure pipe is sufficiently supported.
Unshielded couplings are to be avoided because they tend to offset and sag, but, in your case, you'd have to make the call.
O.D. of plastic 10" pipe may be a challenge to find in a coupling, so keep that in mind.
You don't say if the pipe in question is fully connected to each of the 2" connectors on the units or if the 10" is just a combustion air feeding a larger room.
I doubt it is large enough if it is the only screened opening for combustion air.

 

[ratsandtats]

The combustion intake is 10” galvanized (I believe) on the outside of the building, and breaks of into 8 individual pvc branches when it reaches the heaters. They are directly connected to the navian units. A 10” fernco has been ordered for me to use as a connector for an additional 5 ft of 10” galvanized.

Thank you for the response…it’s actually not my call, I just get to do the work.