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I cleaned out the inlet screen, piped 2 26-99 in series. I'm now getting better results but nothing consistent as far as flow rate.

Now I have one pump away and one toward the boiler. Do I need to have both pumping away from the boiler?

Please explain the purpose and function of a "bypass". Two guys have suggested it and I suspect I might learn something here.



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  • Tankless Rinnai in Hydronic Application

    I don't know about the rest of you, but I have had nothing but trouble trying to use tankless water heaters for hydronics. Here's my latest money-wasting scenario:

    I have a house that will have a NG Vitodens 200 15-60 and Vitocell for DHW and aprox. 30) 250ft radiant circuits in 7 zones. Total heat loss is somewhere around 70MBH. The NG is not yet hooked up as the house is not yet finished and I have been asked to slowly bring the concrete subfloors up to temp prior to and just after installation of hardwood floors.

    Okay. I bought a Rinnai 2532 (to8.4GPM) Propane tankless water heater, hung it on a wall outside, piped my radiant loads primary/secondary. My goal is to bring the floors slowly up to 82°. I installed a 15-58 pump on my secondary and am getting 1/4GPM through each radiant loop. No problem.

    My problem is that I cannot seem to get enough flow through the Rinnai to make anything happen. I want 5-6GPM. The published pressure drop for that unit is 10ft./hd at 6GPM. I have a 26-99 in the primary loop (50ft. 1" pex each way to the Rinnai) I am getting 1.5GPM through the boiler! I quickly installed another 26-99 in series and got 1.9GPM! Has anyone EVER had success pumping water through one of these, because I haven't. According to the pumps' performance the head through the ***** thing must be something like 70 ft./hd! Can that be true?

    Help please. Any suggestions?

    I thought about parallel pumping but I think I have a head problem not a flow problem.

    What say ye?

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  • Ken_40
    Ken_40 Member Posts: 1,320
    You neeed a

    Bypass around that water heater lad. A simple valve array will allow you to dial-in the actual dT
  • Mark_77
    Mark_77 Member Posts: 1

    Have you checked the filter screen, in the water inlet to the heater? Sometimes they can get plugged up.
  • BartMan
    BartMan Member Posts: 4
    Sounds like

    the debris filter on the cold water port is plugged. Or there is some other flow restriction from the installation proccess. Check the filters or call Rinnai Tech support, that heater is probably not the best choice for that application but they will work.
  • Jerry_15
    Jerry_15 Member Posts: 379

    You can't install pumps of different capacity in series, all you get is cavitation and oscillation. Two of the same in series gives twice the head, same flow. In parallel, twice the flow, same head. If you pump away from the boiler, and put in a bypass between the pump and boiler on the suction side, you should have it all, and you can't push more flow through a tankless. Sucking a malt through a straw. You might get away with just the 99. Kill the power to the other one for a quick test before repiping. Good luck.
  • JackFre
    JackFre Member Posts: 225
    I've found

    That a 009 will give 5-6 gpm through a 2532. You want a high head, low flow pump. I don't know the curve on that which you reference. They tend to work best pumping thru the Rinnai. Be aware that the "gpm X delta t x 500 = btu" can play on you pretty good. I'm assuming your delta t is pretty high.
  • JackFre
    JackFre Member Posts: 225
    Missed your ft of head

    I do not have the chart with me and my computer is not co-operating. You are incorrect on 6gpm at 10'head. It is way off. More like 26-30 ft I think. Go to www.rinnaisolutions.com, select the R85I (2532), select "charts and calculators" and your correct pressure drop/flow chart is there.
  • Correct

    You are correct. I was reading PSI at the left of the chart.

    Nevertheless, the Grundfoss is equivalent to a 0013 and is rated at 6GPM @ 29 ft/hd. Now I do have 50'of return and 50' supply piping so there's some head loss there. But two of them in series --- I should be getting all the flow I need. Flow rates at 95° or so seem to be 6GPM at times little more than 3GPM at others. I believe the lines have been well purged and this is not the first time I've a hard time trying to get these things to act like a real boiler.

    I have a customer who wants me to use one of these for an indirect. I need 6GPM that I can count on.

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  • kevin coppinger_4
    kevin coppinger_4 Member Posts: 2,124
    why not just....

    save a whole lot of money and use a propane tank water heater...less hassle...kpc

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