|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
|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.|
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.