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Thread: Paloma PHH-32DV condensing Tankless water heater installation

  1. #1
    DIY Junior Member saphman's Avatar
    Join Date
    Jan 2012
    Northwest Florida

    Cool Paloma PHH-32DV condensing Tankless water heater installation

    Hello All, This is my first post here on the forum. I have spent many long hours searching the internet for assistance on the installation of this tankless heater. I am replacing a conventional natural gas 50 gallon heater with the Paloma PHH-32 Condensing series tankless. The new heater is .90 % + efficient and vents with 3" PVC. My installation is such that I am planning to use the existing roof jack/penetration in my roof from the old heater to vent the new tankless heater.

    The Paloma has two pipes. One is the 3" Air Intake, The other is the 3" exhaust. I purchased the PVC Vertical Concentric termination Vent pipe kit so I could combine both the exhaust and air intake pipes into one roof penetration. My question is this: My installation will be Straight up Vertical with the two 3" Pvc conduits, Up thru the heater closet and then straight up thru the roof.
    I could not get a clear answer from Rheem whether this is ok. The manual mentions a condensate trap on a horizontal run of the air intake. Can I run my vent system straight up or do I need to actually create a horizontal section for the trap.

    Also on the Concentric termination vent that goes thru the roof there is no rain cap or cover on the exhaust vent. That means rain water will spill into the heater. How do I correct this or is rain water entry allowed into the exhaust?. I really want to do this installation right the first time and I appreciate everyones assistance. I would look forward to your comments. Thanks!!

  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    Is there any reason you're not side venting it?

    I'd be surprised if Paloma didn't have a termination cap to deal with concentric vertically vented installations, but if you ran the intake & exhausts separately you can use an inverted U the top to prevent rain penetration. See page 8. A U at the top of the termination kit you bought may have issues with exhaust mixing with the intake- don't do it unless you find it in the fine-print, but a simpler rain-cap might be OK.

    If you're replacing a 50 gallon tank you'll almost certainly have to upgrade the gas plumbing to a bigger diameter for the 199KBTU/hr burner. Don't be fooled by the 3/4" gas hookup.

    With 3/4" gas piping the tankless has to be within 20' of plumbing from the gas regulator, and that's counting ever ell as 2.06' and every tee as 4.12'.

    With 1" you can push that to ~60', counting ells at 2.6' and tees at 5.12'.

    Most big-burner tankless heater installations will need 1-1/4" to work (as in work well), 1-1/2" or more if there are any other loads teed along the path (either before or after the tankless.)

    You may be better off calling in a pro to install it- somebody who has the tools knowledge and experience for debugging it. It's more expensive to pay somebody to rip it out and start over than to get a good plan of attack ahead of time. You may be able to find somebody willing to give on-site guidance, tell you what you need and let you do the work, but they should also inspect it before you turn the gas valve and throw the power switch This burner is about 4-6x the burner of a tank heater, and bigger than that on most home-heating boilers & furnaces, and being a modulating burner it's more sensitive to the supply line pressure (and pressure spikes/drops) than dumb 80% bang-bang on/off furnace burners. The fuel pressure drops are best measured under a variety of conditions and combustion efficiency tested as part of any real commissioning of the unit. There are a thousand ways that it can kinda-work or be almost-right and still bite you in the end. (In some states DIYers aren't even allowed to do their own gas line plumbing- not sure what the status is in FL.)

  3. #3
    DIY Junior Member saphman's Avatar
    Join Date
    Jan 2012
    Northwest Florida


    Dana, thanks for the reply. I am venting this vertical as that is where my current water heater vent pipe is now. I was planning on using that existing access. As I mentioned earlier, it is straight up vertical to the roof jack. One of my main concerns is the PVC vent system. I did purchase the 3" concentric termination kit. There is no rain cap on the top of it. The vent is wide open and rain will come down that pipe. How do you fix that? I cant get a clear answer from Raheem. Putting a "u" on it will cause vent gases to mix with the intake.

    My entire house is all gas and the gas company installed a 2lb meter. I have regulators at each outlet where there is an appliance including my existing water heater. the plumber that did the original install felt there would be enough gas flow / pressure to use this heater.

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