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Boiler with indirect water heater only

roberto764
roberto764 Member Posts: 2
in Domestic Hot Water

I am going to be installing a Lochinvar Noble 199 boiler with a 110 gallon indirect tank. The boiler will only be used to heat the indirect tank.

What would be the best way to do the hydronic plumbing? I was thinking of just doing a full flow with the boiler circulator pumping the water through the indirect, but then got to thinking about when the tank temp is met and the boiler shuts off the boiler circulator will continue to run for the couple minutes during cool down and that water will still be circulating through the indirect tank.


So what would be the best way to do this? Primary and secondary loop (which seems kind of overkill since it’s only one zone)? Zone valve?

Thanks

Comments

  • Kaos
    Kaos Member Posts: 603

    I would connect it directly to the boiler with a single pump in space heat mode with fixed output say 160F. Run the indirect aqua stat to the tsat input on the boiler.

    I would check your gas supply as that unit needs a bigger supply than a standard water heater.

    An indirect in DHW mode is about 80% efficient, maybe 85% if everything configured right. That is similar efficiency as a power vent tank and less efficient than a tankless unit. It is also about 2x to 3x the BOM cost of either option and significant labor.

    It makes sense only if you are looking to add space heat to it down the road.

    Alan (California Radiant) Forbes
  • hot_rod
    hot_rod Member Posts: 24,967

    Do you know how much DHW you are trying to generate? With a hi performance tank, lots of coil surface, you can generate DHW at a lower boiler opertating temperature. Possibly get in condensing range.

    Take a look at some of the HeatFlo high and extra high output tanks.

    This example with 150 SWT

    Pump directly from the boiler to the tank coil. No need for zone valves.

    Is this boiler going to supply heat at some point? If so the piping should be designed to accomodate that.

    Screenshot 2025-04-24 at 7.33.00 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • roberto764
    roberto764 Member Posts: 2

    This is actually in a plant where in this section of the plant the hot water is provided by a steam heat exchanger and the steam comes from a boiler room about 400 feet away. So we are going to get rid of the steam heat exchanger and go this route. The exchanger was undersized from the start and it’s hard to keep enough steam in it in the winter time to keep it working half way ok.


    It’s hard to nail down an exact dhw usage as it is used for clean up and hose water and that usage can vary day to day. This is the only thing this boiler will be used for. To heat the indirect for dhw.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,807

    Hi, I'm trying to understand this. Wouldn't it be less expensive and simpler to go with a commercial, underfired, tank-type water heater? You could add a second tank and circulation if needed. 🤔 I feel like I'm missing something in the decision making process.

    Yours, Larry

    ethicalpaulAlan (California Radiant) Forbes
  • GroundUp
    GroundUp Member Posts: 2,341

    That's a LOT of hot water. But if that's what it needs, yes just pipe it direct to the boiler in 1-1/2" with a Grundfos 26-99 or equivalent and wire the circ to the orange "DHW pump" output in the junction box underneath the boiler. You can adjust the post-purge time in the settings but they are 30 seconds or less from the factory, I have never timed it. No harm in letting it post purge a little bit to scrub any excess from the exchanger. Easy peasy.

    hot_rod

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