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Installing a Combi Boiler without using the heating part for a while

hotsaucehotsauce Member Posts: 5
New to this board so I hope I dont commit any violations. We just moved into an older house. The existing water heater is leaking badly and probably going to fail more catastrophically sooner than later. To replace it I bought a Navien NCB-180e which is a combi boiler. It is my intention to install this asap to replace the failing hot water heater but for the time being I only intend to use the DHW side of the boiler. I bought the combi boiler so I could plumb the heating side to radiator and baseboard heaters later this year but for now other priorities prevail.

Will there be any problem with running this combi boiler but only using the DHW side for now? I am thinking this should be OK as the situation will be similar to a summer shutdown of the heating side while continuing to use the DHW side but I worry about protecting the heating side heat exchanger which is primary in this unit.

Are there any special precautions I should take to ensure that the heating side wont overheat when I am only using DHW? Should I hookup a temporary primary loop or something similar?

Comments

  • IronmanIronman Member Posts: 3,542
    edited October 2
    You will need to hookup the back flow/fill valve; the expansion tank and the relief valve at minimum on the boiler side.

    What is the heat loss of your house? The NCB may or may not be sufficient the supply enough btus for baseboard at design temp.
    Bob Boan







    You can choose to do what you want, but you cannot choose the consequences.
  • kcoppkcopp Member Posts: 2,774
    edited October 1
    The IBC DC combi boiler has 2 coils through the heat exchanger. One of the benefits to this unit is that you dont need to do any heat-side piping period to use the hot water. Gas, vent, hot and cold piping then power it up and you are off....
    I have done this a few times to get hot water on to the home fast during an install.
    Prob the most underrated unit on the market.
  • hotsaucehotsauce Member Posts: 5
    Thanks kcopp - Did you really mean IBC DC? I have an NCB-180e.
    Cheers
  • Bob BonaBob Bona Member Posts: 2,081
    You've got to pipe in the secondary manifold kit, air seperator, feeder, expansion tank, you can valve off the supply and return piping after that. The boiler has to be under pressure and air free on the heating side to operate for hot water.
  • kcoppkcopp Member Posts: 2,774
    hotsauce said:

    Thanks kcopp - Did you really mean IBC DC? I have an NCB-180e.
    Cheers

    Yes I meant IBC-DC... Can you return the Navien?
  • hotsaucehotsauce Member Posts: 5
    Ironman said:

    What is the heat loss of your house? The NCB may or may not be sufficient the supply enough btus for baseboard at design temp.

    Thanks Ironman! Yes, I have a full Manual-J study so I have heat loss/loads (and cooling) for each room. The 180e will deliver and hold 180 f without overrides and will hold 195 f if you tweak a few things. Man-J says this is more than adequate if not downright overkill for my climate zone and the panel radiators and baseboards I have selected (Slant/Fin).
  • IronmanIronman Member Posts: 3,542
    edited October 2
    hotsauce said:

    Ironman said:

    What is the heat loss of your house? The NCB may or may not be sufficient the supply enough btus for baseboard at design temp.

    Thanks Ironman! Yes, I have a full Manual-J study so I have heat loss/loads (and cooling) for each room. The 180e will deliver and hold 180 f without overrides and will hold 195 f if you tweak a few things. Man-J says this is more than adequate if not downright overkill for my climate zone and the panel radiators and baseboards I have selected (Slant/Fin).
    Uh, you're missing some pieces to that puzzle:

    First, any boiler (except the Vitodens) will supply 180* water. But that makes the boiler operate at 86% efficiency. If you're installing new radiation, it should be sized so that the RWT to the boiler doesn't go above 140*. This way the boiler will condense ALL of the time and the efficiency will be at or above 93% all of the time.

    Second, water temperature is just one component in factoring how much heat can be delivered. If it were the only factor, then why use a 180k btu boiler? Why not a 50k btu boiler? They both make 180* water.

    Third, let me give you the universal hydronics formula:
    Btus = (gpm X 500) X delta T.
    From this you can see that flow (gpm) is a factor in how many btus you get. That's why a 180k btu boiler can deliver more btus than a 50k. Not only does the 180k have a larger burner to input more btus, but it needs more flow (gpm) to remove the btus and carry them to the radiators.

    Now, here's the point: the onboard pump on the NCB can deliver about 6 gpm if memory serves me correctly. It's limited to that because it has to be sized for DOMESTIC water heating. There is a much wider delta T (temperature difference) when heating domestic: 50* incoming; 125* out. That's a 75* delta T. Plug it into the formula above and you'll see that you only need 4.8 gpm to get 180k btus. Remember, a 75* delt T.

    Normally, medium to high temp American hydronic systems are designed for a 20* delta T. Plug that into the formula and you see that you get 48k btus at 4.8 gpm or 60k btus at 6gpm. It doesn't matter that the burner can produce 180k btus, the flow can only carry 60k at 6 gpm. Remember again, the onboard pump can only move 6 gpm.

    The only way that you can get more btus to the radiators is to DESIGN them around a higher delta T between the BOILER'S supply and return. It is possible to design the system so that the radiation sees a 20* delta T while the boiler would see a 30* delta T or more. Again, this involves sizing your radiation to give the needed output at a lower SWT and sizing the secondary circulator and piping so that it has more flow than the boiler loop.

    What is your TOTAL heat loss for the house?

    Bob Boan







    You can choose to do what you want, but you cannot choose the consequences.
  • hotsaucehotsauce Member Posts: 5
    Ironman said:


    What is the heat loss of your house? The NCB may or may not be sufficient the supply enough btus for baseboard at design temp.

    Thanks Ironman - I have a full Manual-J study so we have detailed heating and cooling load/loss data for each room of the house. The NCB-180 is capable of delivering a max constant heat of 180 f (and more if you tweak the settings) and its BTUH output is more than adequate by the Man-J figures for my climate zone and this houses loss profile.
  • hotsaucehotsauce Member Posts: 5
    Thanks Again Ironman - outstanding explanation. Sorry I couldnt respond sooner. We spent a final week camping in the high country before winter sets in and just got back.

    Man-J reports a total heating load of 48,017 Btu/hr. I bought an NCB-180, which at first glance seems to be overkill, to address the very issues you are referring to. I also do not plan on using the built-in circulation pump and have designed in a Taco or Grundfos ECM-based pump that can pull more GPM's when called for. Lastly I have a large buffer tank in the primary loop that will supply all heating zones and circuits through secondary circulation pumps pulling out of the buffer tank.

    I used HeatCAD and LoopCAD to compute all of the flows in the system taking into consideration the CV of all the piping, joints, fixtures, and devices. The resulting numbers will determine the size of the circulation pumps required throughout the system. HeatCAD also gives me the heat losses of all components and systems and computes the return temps for a given supply temperature. I have one mixing valve in the return loop to ensure that the return temperature is in the condensing boilers sweet spot.
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