Adjusting Inclination of Navien Exhaust Pipe

See a previous post for an explanation of why this repair is being done.

Removing Navien connection to exhaust pipe

Sheet rock cut out around inlet and exhaust pipes

Condensate (~1.5") trapped in exhaust pipe

Original set of exhaust pipe

Exhaust pipe hole expanded and pipe lowered

Cover placed over open sheet rock space

Piping refit to Navien

Water Collecting Under Wall Below Navien Tankless Hot Water Heater

We've noticed water collecting under the baseboard below the Navien Hot Water heater. The problem is intermittent; it isn't constant, and it's a small amount of water. We've noticed the water collecting during the day, when water is being used in the house, and when the heating system is more likely to be running. As an example, there was water on the floor along the baseboard yesterday. The water had dried up overnight.

Although the water is below the tankless hot water heater, it isn't coming directly from piping on the hot water heater itself. We've checked the hot and cold water piping, the drain, and cycled the pressure relief valve (in case water is splashing), and found no leaks. The water is definitely collecting inside the wall.

Water is collecting along the baseboard below the Navien
tankless hot water heater. Notice the vent on the wall.
Cold air pours through this vent during the winter.

The water runs all along the baseboard.

Drains (black), main water (blue), and plumbing
for the tankless hot water heater

Drain pipes

Intake and exhaust for tankless hot water heater. Line above
white pipes is HVAC power and condensate drain.

Exhaust goes into garage

and up garage wall

up through roof

Installation of vent ducting.

Installation of Navien tankless hot water heater.

Navien tankless hot water heater as it stands
today. Line above system is condensate drain
from furnace and power to HVAC units outside.

Condensation line exiting storage room to outside under deck.

Condensation line drain by AC unit.

Given the situation, the best guess as to the nature of the problem is condensation forming on the cold water pipe inlet coming to the Navien unit from inside the wall. There's also possibility of condensation forming on the exhaust pipe from the unit.

Pipe insulation can prevent condensation forming, as the surface temperature of the insulation will vary from the surface temperature of the pipe. Condensation will not occur, provided that (a) the insulation surface is above the dew point temperature of the air; and (b) the insulation incorporates some form of water-vapor barrier or retarder that prevents water vapor from passing through the insulation to form on the pipe surface.

Of course, another possibility is a slow leak in one of the water lines. The fact that the problem just showed up in the winter cold weather seems to mitigate against this, but doesn't rule it out.

The Navien Tankless Hot Water Heater

We're having a tankless hot water heater installed in our new house. These systems heat the water only when needed, rather than keeping a supply of water heated all the time. We used this sort of system when we lived in Vienna, Austria, and it worked fine for us.

The diagram below shows how the system works.

1 - Exhaust

2 - Heat exchanger

3 - Burner

4 - Fan

5 - Control panel

6 - Flow sensor

7 - Hot water to faucet

8 - Gas supply

9 - Cold water coming in

10 - Cold water to faucet

Plumbing for tankless hot water heater in in storage room downstairs

The Navien tankless system is much smaller than a hot water heater

The large diameter pipes above the unit are intake and exhaust pipes

The intake and exhaust pipes for the Navien exit the house under the deck. A chase has been built to hide these pipes.

The exhaust pipe travels along the back wall of the garage up to the roof 

Bottom of the Navien unit showing water inlets and outlets, as well as circulation inlet, and gas inlet.

Navien energy guide

Navien cover has been removed to permit testing

Closeup of insides of Navien unit

Mother Board -- Error codes show on display (showing 8888)