Navien Pipe Length

[RobertK]

Just found the forum, thanks for the add. I'm having a Navien NPE210A installed in my basement next week and have a PVC pipe air resistance question.

My plumber chose the install location based on what he feels is the best location for the unit and ease of install. He's using 2in PVC through the wall of the house for air intake and exhaust. The PVC pipes will each have four 90deg elbows and around 5 to 6 ft total PVC of combined vertical/horizontal pipe.

On paper pipe length is 37 ft but by tape measure its still 5/6 feet. I live in the North East and its freezing right now . I'm concerned with the pipes being so short that any wind blowing into the them will come into the unit and will freeze the heat exchange or storage tank during a short power outage. Do 90deg elbows create any type of restriction for air flowing in?

My basement is heated but basically I'm concerned that with freezing air blowing in them the PVC pipes are to short during a power outage when the units freeze protection can't activate. The only thing Navien mentions about his is to increase the pipe distance, which may not always be practical. Just looking for real world ideas/opinions.

I am currently in "discussion" with my plumber on types termination ends, any help here would be appreciated. I know they have battery back power up units but its already getting expensive and I'm slightly tempted just to stay with my current natural vent set up.

Thanks for any help or suggestions

 

[Breplum]

It would be great if your plumber had real world experience with this challenge.
Your make a good point. This said from a geo-location that never has this issue.
If no luck here, I suggest that the plumber discuss it with the local Navien reps or other colleagues.

I am a complete Navien fan and tech level three trained, but truly, you don't really get a payback on tankless unless you live with it for twenty years. But after factoring in descaling and the more moving parts to break, the only real advantages are:

1. good recirculation if you have dedicated recirculation pipe.
2. it is green to not waste gas
   
3. unlimited hot water

But it still creates greenhouse gas emissions. Heat pump water heaters are greener by far...

 

[Sponsor]

 

[Bannerman]

The Navien NPE 210A Installation Manual specifies each 90-degree 2" elbow is equivalent to 8 linear feet of pipe. Each 45-degree 2" elbow is equivalent to 4 linear feet of pipe.

If the exhaust or air intake pipe each utilize 6' pipe and two 90 elbows, then that will be equivalent to 22' straight piping distance for each.

Wind blowing through the unit will not be an issue when both the air intake and exhaust vents are terminated through the same wall. Any wind against that wall will place equal force against both vents so without a pressure differential, wind will not blow through the unit.

If the air intake and exhaust vents are not terminated with the same building exposure, then a pressure differential is more likely to exist which can result in the situation you are concerned with.

 

[RobertK]

It would be great if your plumber had real world experience with this challenge.
Your make a good point. This said from a geo-ocation that never has this issue.
If no luck here, I suggest that the plumber discuss it with the local Navien reps or other colleagues.

I am a complete Navien fan and tech level three trained, but truly, you don't really get a payback on tankless unless you live with it for twenty years. ..

Thank you for the response. Im not considering payback time as it will probably be a loss for me in the end. The biggest factor is that my current water heater is just "in the way " of my basement set up. It was put in a bad spot when they built the house and since I refinished the basement it has only gotten worse. We are constantly hitting it when we try to put stuff in the crawl space. A tankless would solve my issue. My other option was going with a power vent but I dont have the 4ft exhaust vent clearance they call for. I had three plumbers out for estimates and this guy seemed to understand my concerns and is Navien certified.

 

[RobertK]

Wind blowing through the unit will not be an issue when both the air intake and exhaust vents are terminated through the same wall. Any wind against that wall will place equal force against both vents so without a pressure differential, wind will not blow through the unit.

Thank you for the answer. I did read the manual and do understand the part about pipe length with elbows. Both pipes will exit the house through the same wall, possibly even the same joist spacing. From there they will point in different directions and both will go vertical to above the snow line. The vent pipe will be higher to meet the 12" distance from the intake opening.

So do both pipes have to be terminated the same way? For example if the intake terminates in a 90 deg elbow pointing down but the exhaust is a 45 deg pointing straight forward will they still equalize? I guess what Im not understanding is that the intake pipe comes into the unit and air is freely flowing inside the unit while the exhaust pipe is sealed in the chamber. How does this equal out?

Thank you

 

[Bannerman]

The air intake with an elbow facing downward is intended to prevent snow/rain from being sucked into the pipe whereas with exhaust, warm gases will be forced outward. Even with an elbow on the intake vent, wind forces against the building where both vents terminate, will be virtually equal on both vent openings. Without a pressure differential between them, there will be no air entering one vent and exiting the other while the unit is not operating.

A fan located prior the Navien's exhaust connection will ensure products of combustion will be removed from the combustion chamber and will be forced out from the exhaust pipe to atmosphere. The air entering the combustion chamber for both gas combustion and to supply the exhaust fan, is obtained from within the unit's sealed cabinet. Although the air within the cabinet will be sealed from entering your home's interior, it is not sealed off from the combustion chamber or the exhaust vent connection.

While cold air from the exterior will be drawn into the cabinet, this will be occurring only while the unit is operating and producing heat so there will be little opportunity for water to freeze within the cabinet enclosure located within a heated area.

 

[Dana]

Tankless freeze-up issues are usually only a problem when the combustion air is drawn from the indoors, in homes where the tankless is installed in a basement. In those configurations the whole-house stack effect pulls air out of the top of the house and pulls air in at the bottom of the house in winter. When the burner is not operating there is a steady trickle of outdoor air coming in the exhaust port, through the tankless and into the house. Under various wind conditions the air flow through the tankless becomes even higher than through stack effect drives alone.

But with the piped-in combustion air port terminating near the exhaust vent the air pressures are fairly equal- with effectively no stack effect, and no wind pressure differential.

 

[RobertK]

Thank you both for the help. I do feel a little better about the decision now.