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Best Combi Boiler with Cascade Option

Hello!

First time poster here. I've been looking around for some information on cascading combi boilers and just haven't been able to find answers. Found this site yesterday and there seems to be a ton of useful info. Now on for my question.

Currently I have a Navian NCB-240E. I love it. Had it install two years ago along with radiant floor heat.

My heat loss is about 100btu currently but now I am looking to add radiant to my basement (currently use a pellet stove) which will push me past what the NBC-240E can handle.

At first my plan was to simply add an additional NCB-240E.

The problem is that Navien doesn't allow you to cascade two NCB models. You can add their space heating only or DHW only models but not combi.

On the surface thats fine, I could just add the space heating model. But now I am finishing my basement and will be adding another bathroom. So I wanted the additional DHW capacity as well.

This got me looking around and I really like the Lochinvar NKC199N.

So that is the backstory.

Started to read the manual on the Lochinvar and it does cascade but only on space heating not DHW.

With all that being said I have two questions.

1) Would simply two of Lochinvars work by cascading the space heat and then running the DHW from both at the same time? If I'm pulling 5gpm it would just pull 2.5gpm from each at the same time correct?

2) From my research I can't find any combi that does cascading on both space and DHW, do you know of any that do?

Thats all for now. Thanks so much for any input.

Comments

  • bob eck
    bob eck Member Posts: 928
    The Navien NBC-240E has 125,000 BTU input for heat with 199,000 BTU input for domestic hot water.
    Lochinvar Noble NKC199N will have an 199,000 BTU input for both heating and domestic hot water. No need to install two combi boilers. This Noble boiler will deliver 4.8 GPM at 77 deg F temp rise. Should be able to run two showers at one time.
    If you need a larger domestic hot water demand do one condensing boiler with an indirect water heater.
    DZoro
  • justaphotoguy
    justaphotoguy Member Posts: 3
    I would like to have the additional dhw. Upwards of 7gpm (it's a big house).

    The reason I want to go with two combis is to have redundancy. If one goes down I still got one running.
  • bob eck
    bob eck Member Posts: 928
    Are you on city water? If you have your own well does you pump even deliver 7 GPM?
    I you really want redundancy install two heating only boilers and install one 80 gallon or 119 gallon indirect water heater. Store the water at 140 or 160 degrees and put an mixing valve on it to send water out to the showers at 120 degree.
    You can get a Vaughn indirect water heater with electric elements in it so if the boilers go down the electric elements will still produce hot water.
    DZoro
  • Wellness
    Wellness Member Posts: 123
    Second what bob eck said, although I set my DHW tank at 130 at night and at 140, 90 minutes before expected usage in the morning. At 140 °F Legionellae die within 32 minutes.
  • justaphotoguy
    justaphotoguy Member Posts: 3
    bob eck said:

    Are you on city water?

    Yes.

    Due to renovations I don't really have the room for a tank. I could do a tankless water heater on the wall but why not just stick with a combi?

  • BigEHead
    BigEHead Member Posts: 11
    what did you end up using? I have a larger house and want to convert to a cascaded setup of 2 combi boilers. thanks!
  • bob eck
    bob eck Member Posts: 928
    BigEHead
    What is your heat loss.
    Navien NFC 175 and NFC 199 combi boiler.
    I believe you can add another Navien tankless gas water heater to get more GPM for your domestic hot water needs.
  • BigEHead
    BigEHead Member Posts: 11
    edited January 25
    Thanks Bob Eck.  I am not sure of my heat loss.  I've looked up tons of brands but the only one that seems to cascade a combi and a tankless water heater is Navien.  I currently have 2 - 75 gallon tanks and an old Weil McClain boiler for hydronic heat.  The other option is sticking with just a condensing boiler and have 1 or 2 indirect tanks.  I haven't seen 2 indirects piped with a boiler though. I'd prefer the combi and tankless cascade but I'd go with 3 separate units since they all modulate.  The initial costs would be the biggest hit. Thoughts?  I appreciate it!
  • bob eck
    bob eck Member Posts: 928
    You can get a 70 or 119 gallon indirect water heater that would have two coils in the tank. 
    Store the water at 160F and mix down to 125 F going out to your faucets. 
    Reduce your shower heads to 1.5 GPM 
  • BigEHead
    BigEHead Member Posts: 11
    So you think a condensing boiler and an indirect?  Are there brands you recommend for both?