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EK Hi-Mass/Low-Mass Kit: Layman's Explanation

wjcandee Member Posts: 3
Here on Long Island, we are close to pulling the trigger on replacing our 70+ year-old Fitzgibbons oil/water boiler (and Bock HWH) with an oil-fired EK2 System 2000 with an 80-gallon HW tank. The Fitzgibbons is a beast, running dual 1.75gpm nozzles, and might run for 20 minutes in an hour when it's 15 degrees outside. Obviously way-oversized. Had a Manual J done, which computed 190K heat loss, which I think is high. (On a 0/0 day, we would use at most 45 gallons based on K-factor. Doing the math, if that boiler is 60 percent efficient -- a stretch I think -- then we're putting 154,553 BTU/hr into the system on a 100-year cold day.) One advantage of the EK2 is the ability to adjust nozzle size to get the actual output where it's going to be most-efficient. Reassuring when I have multiple differing estimates of how large the boiler should be.

House is long with boiler in the middle, so it has two zones, each with a 70-ish-foot run from the boiler, one East, one West. Cast iron radiators exclusively. 3500 sq ft 1st floor footprint, duplicated on second floor. I do notice that in mild weather, the boiler quickly satisfies a call for heat, so the radiators on the end of the runs do not get fully-warm before the boiler shuts off. They get very hot when the thing is pounding away on a cold day. (A better-sized boiler probably wouldn't do this, because it would run longer on a mild day, so it's not clear that this issue wouldn't be addressed simply by downsizing the boiler. I just don't know.)

So, my question: In simple terms, what would be the purpose of including the EK High-Mass/Low-Mass kit in this install, and how would it help? It appears to be essentially a primary/secondary loop injection; I'm just not clear on whether/why to include it. Can somebody explain and make a recommendation in a few sentences? I would be very, very appreciative!

Thanks for all the wonderful information I have read on here over the years.


  • Alan (California Radiant) Forbes
    Often the ideal system flow is not the same as the ideal boiler flow; the two might not get along.

    The EK High-Mass/Low-Mass kit (aka primary-secondary piping) allows the boiler to circulate independently of the system.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • wjcandee
    wjcandee Member Posts: 3
    Thank you! I really appreciate it. Any sense of whether given our circumstances it might be a good thing to have? Or is more information needed? Again, thank you so much.
  • Jamie Hall
    Jamie Hall Member Posts: 23,544
    What is your radiation? Cast iron big radiators? Cast iron baseboards? Fin tube baseboards? Those three -- and others like them -- are arranged there in order from high mass to low mass. The EK boiler is low mass. Now -- what is the significance of that? Simple this: high mass devices respond slowly to changes in the temperature of the water supplied, but retain heat. Therefore they work best with the circulation going for a nice long time at just the right temperature to heat the space, whereas low mass can respond quickly both ways. The EK kit makes it much easier to match the relatively long run low temp required by the radiation with the relatively quick response of the boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • szwedj
    szwedj Member Posts: 66
    Everyone's comments are pretty much spot on.

    The high mass/low mass (primary/secondary) kit from EK is really just a pre-made injection header kit that includes a loop circulator that EK has available to make the install a little easier. It is a popular option used by installers when connecting to large water volume cast iron systems.

    It's basically a very efficient way for a low mass boiler to evenly heat up a large water volume system. When the heating zone thermostat calls, besides giving the boiler a heat demand, the system manager will start a loop circulator on the heating zone to get the water circulating throughout the zone. The manager also controls how the boiler injects the hot water into the loop. This results in very even heating of the loop, allows the manager to provide condensing protection to the boiler and to post purge the heat in boiler to the heating zone once the call is satisfied.
    Joe Szwed
    Energy Kinetics
  • wjcandee
    wjcandee Member Posts: 3
    Thank you, everyone! As I mentioned in the original post, we have exclusively cast-iron radiators, and long runs, so presumably a lot of water to be heated. Our giant boiler heats that water quickly, and probably excessively, under most conditions. Except when it is quite cold outside, the radiation at the end of the loop doesn't heat much by the time the closer radiators (near the thermostats) have satisfied the call for heat. The explanations above, especially how EK integrates the package's operation with the System Manager, make a lot of sense and make me think that this is something I should ask the installer to consider.

    Thank you all again so much!