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  1. #1

    One Tankless Water Heater for Hydronic & Potable?

    Hi to all those wiser than myself,

    My Plumber is an excellent craftsman but is lacking in knowledge in this matter, so here I am. I am interested in installing a Rheem RTG-66DVN (Paloma PH-25RDVSN) Natural Gas Fired Direct Vent Tankless Water Heater in my Single Bath, Single Story (with finished basement) 1200 square foot Home located in Long Island, NY. The main floor in my home has Forced Air Heating via Gas Fired Furnace, but the 3/4 Finished Basement has Hydronic Baseboard Heating via 30 gal. Gas Fired Water Heater. My question is: Is it possible to run (plumb) the homes Potable Hot Water and the Basement Hydronic Baseboard Heat to a Single RTG-66DVN Tankless Water Heater? I live alone, so there is not a great Hot Water Demand. And the Basement Hydronic Baseboard Heat is used only occasionally in the Winter months.
    Last edited by VIPSpecialNeeds; 07-29-2009 at 07:18 PM.

  2. #2
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    The first thing that comes to mind is the gallons per minute rate of the heater. You would need to figure the Btu/hr needed and see if you have enough water flow to transfer enough heat.

    The next thing is that with the small heaters, they can have resistance to water flow. You'll need a good high head, low flow pump. Brass, not iron. You'll have to match a pump curve against the system curve.

    Because you'll be heating in a loop, you will need to bleed air bubbles and provide for flushing scale.

    This is a job that requires more than a heater and a pump.

    And, your warranty will go from (I think) 10 years to 3 years because the heater is being used for continuous operation.

  3. #3
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,039
    They make units that will do just what you're wanting to do. Hydronic and potable water from one unit.

    The only one that comes to mind right now is:

    Quietside DPW dual purpose water heater
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    May 2009
    Posts
    196
    Quote Originally Posted by VIPSpecialNeeds View Post
    My question is: Is it possible to run (plumb) the homes Potable Hot Water and the Basement Hydronic Baseboard Heat to a Single RTG-66DVN Tankless Water Heater?
    What's physically possible, what's a good idea, and what will pass code inspection are three very different things.

    It's not necessarily legal to use a water heater as a heating boiler unless it's specifically rated for the purpose.

    Ask Rheem and your jurisdiction's building inspector.
    Last edited by beenthere; 08-28-2009 at 11:21 AM. Reason: Removed links to other forums

  5. #5
    Join Date
    Jun 2009
    Location
    Fairbanks, Alaska
    Posts
    77
    "...What's physically possible, what's a good idea, and what will pass code inspection are three very different things...."
    Good one

    I use a Paloma hot water heater as a boiler once. It was not reliable or especially effecient, probably because it was not designed for that use.

    The domestic hot water system should be all copper and brass or other non corrosive pipe such as oxygen barrier Raypex including the circ pump. If you do that and add the appropriate hydronic equipment it will work.

    A small boiler with a domestic storage tank would be much more efficient and reliable albeit not as cheap up front.

  6. #6

    Still Not Clear...

    Thank You All,

    For the helpful replies, but pardon my ignorance. I am still not quite clear as to how the Domestic Water would stay clear of the Hydronic Heating Water. I was able to find a Diagram (see link below) showing how a single unit would be plumbed to both DHW & HHS, but despite all the check valves, circulators and priority switch I am still not clear as to how it (separation) is accomplished since the heating system would no longer be closed loop. I am also concerned if it would be a problem having the Hydronic Heating Loop remaining idol for long periods of time.

    http://www.plumbingwholesaler.com/takagi/TK2Rad&Dom.pdf

  7. #7
    Join Date
    Jun 2009
    Location
    Fairbanks, Alaska
    Posts
    77
    The problem is that this is not the place to get the instructions.
    Last edited by beenthere; 08-28-2009 at 11:22 AM. Reason: Removed names of other forums

  8. #8
    Join Date
    Jun 2009
    Location
    Lomita, Ca
    Posts
    34
    I have done quite a few tankless installations. I started working with them in 1989 when they were very uncommon here in the States. I have never installed on for heating purposes though . Most manufactures have excellent resources on their websites, with detailed drawings, for many hydronic applications.

  9. #9

    Dual Purpose Fix

    Click on this link below to find out all you need to know about Dual Purpose water heaters that provide both space heating and domestic hot water.

    http://www.quietside.com/Quietside/i...&id=50&Itemid=

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