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Old 01-07-2014, 09:28 AM   #1
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Drill hole in conentric vent for tankless water heater?


I have a recently installed Rinnai RU801 Tankless Water Heater. The WH was installed with the concentric vent option. The WH is mounted on an interior wall, and the vent goes directly to a 90 degree elbow, then slopes UP to the exterior wall over about a 10 foot distance, then 90s up, second 90 to horizontal, exits the house, then 90s up in a snorkel for about 18" (for snow), then 90's horizontal with the dual pipe outlet/inlet.

The house is still under construction, and the WH has not yet been fired up yet.

I've had some intermittent water drips that appeared on the bottom of the water heater, but I was not able to determine the source. Yesterday, there was a lot of water on the ground, and I took off the cover and traced the water up to the intake fan. It appears that water is entering the intake air pipe and running down to the tankless water heater (I thought it was wrong to slope DOWN to the water heater, but the instructions indicated that this is how to do it).

I've read the WH manual, and while it addresses condensate from the exhaust, it says nothing about the intake.

I can try to better protect the intake from rain, but is there anything I can do on the intake pipe? Can I drill a hole in the exhaust section of the pipe and run it to a drain?

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Old 01-07-2014, 09:40 AM   #2
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Drill hole in conentric vent for tankless water heater?


you cannot drill any drain holes for safety reasons. sounds like the pipe is sweating and may need to be insulated. not uncommon in cold climates. post some pics of the venting and heater. if the heater was running then some heat from it may keep the pipe warm enough to prevent sweating.

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Old 01-07-2014, 06:15 PM   #3
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Drill hole in conentric vent for tankless water heater?


Post pic of concentric. It may be installed incorrectly.
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Old 01-08-2014, 07:20 AM   #4
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Drill hole in conentric vent for tankless water heater?


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Old 01-09-2014, 04:39 AM   #5
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Drill hole in conentric vent for tankless water heater?


Looks right.

I would have the installer contact Rannai to see if they okay tapping a drain into the intake.
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Old 01-09-2014, 09:51 AM   #6
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Drill hole in conentric vent for tankless water heater?


or try stuff fibreglass pink insulation around the pipe where it enters inside the house for a couple of feet temporarily until the heater is fired up. I think you are getting cold conduction down the pipe from outside causing sweating. may go away once it is fired up and there is heat in there. we insulate the first 3-6 feet of our intake pipe in my area if they sweat. you can leave the insulation in the joist space permanently. You are going to have a SERIOUS problem later if you don't keep all that snow away from the pipes. the exhaust will recirc into the intake and the moisture will destroy the burner from corrosion etc and it won't burn properly or safely. It needs to be 3 feet above the max snow level or relocated to a non snow area.
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Old 01-09-2014, 11:13 AM   #7
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Drill hole in conentric vent for tankless water heater?


Your piping is sweating, due to it is warmer inside, then the surface of the pipe. I just had that issue with the intake on our furnace. Placing two 1500 watt heaters in my basement, solved that issue real quick. No more moisture dripping off of the PVC piping.
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Old 01-09-2014, 11:49 AM   #8
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Drill hole in conentric vent for tankless water heater?


expensive way to get rid of sweating though. usually if you insulate the intake about 6 feet then the air warms up enough and it does not sweat.

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