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Munchkin 199,000 BTU, Is Armstrong Astro 50 enough pump?

JUGHNE Member Posts: 10,914
Asked to service a Munchkin 199. It feeds existing fin tube convectors from the 60's.
No primary/secondary piping, no DHW. All water passes thru boiler.
1 1/4" copper in and out.
The only pump in the system is Astro 50, 108 009365...110 watt, .92 amps.
I could not find specs on the Astro 50 as such.

Seems to cycle a fair amount. High temp cut out is 180.
2 story with a fair amount of BB and convectors.
Does heat OK though.


  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,827
    edited November 2018
    The boiler is cycling because the water isn't moving fast enough to pick up all the heat that the heat exchanger is generating.

    Page 15 in the Munchkin installation manual shows you pressure drop charts and pump selection for the different boiler sizes. Page 16 shows you that for a 199M, it will flow 19 gpm at 17' of head.


    And that's just through the boiler. You have to add pressure drop through your piping, fittings and devices.

    The Astro 50 at top speed comes nowhere close to this:


    A Taco 0011 will do the job.


    A Grundfos 26-96F will also work.

    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
    IronmanSuperTechkcoppdelta T
  • Ironman
    Ironman Member Posts: 7,225
    edited November 2018
    The 011, 013 or 26-96, 26-99 are sufficient for pumping the boiler, but not the house. Every pumping diagram calls for p/s piping. You could use the Astro for the house loop with p/s.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    JUGHNE Member Posts: 10,914
    Thank you Alan and Ironman.
    This has been like this since install in 2010.
    Munchkin piping diagrams do show a single pump w/o PS piping.
    The book is from 2006, build date.

    Just by looking, it looks to be physically small for the job.
    I did install another 199 with P/S with the larger 26-96S.
    Lochs come with the pump included probably for this very reason.

    The installer put the 1 1/4" isolation valves between the pump and boiler. Just another PIA for bleeding air.
    The fan on this failed twice since install, was blamed on rebreathing exhaust because of concentric venting.
    But with this baby pump on it, it obviously ran hotter and longer than needed. Do you think the hi temp contributed to the fan failures?
  • SuperTech
    SuperTech Member Posts: 2,032
    edited November 2018
    I would definitely think it would attribute to it. I've seen a few boilers with the Giannoni heat exchangers fail prematurely when the installers didn't pipe them primary/secondary.

    Flue gas reversion due to concentric venting seems to be another big problem.

    I had a problem with an NTI Trinity where I found the installation instructions had changed regarding the boiler pump size over time due to the high head heat exchangers
  • hot_rod
    hot_rod Member Posts: 20,827
    I've seen a number of old Munchkins piped direct like that, the circulator is undersized for that size boiler, it looks to be about the same as a 15-58.

    I would suspect recirculating flue gas more that 180F operating temperature for the fan failures
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    JUGHNE Member Posts: 10,914
    The header got a lot of attention.

    Thank you all for confirming what I thought.
    Just looking at the pump it was immediately suspicious.

    I see the newer Munchkin piping diagrams all call for P/S pumping for everything. That was a learning curve for all I would imagine.

    Do you all agree with Ironman that the Astro 50 could pump the house with the 0011 or 26-96F for the boiler if set up P/S?
  • hot_rod
    hot_rod Member Posts: 20,827
    If the fin tube is not small diameter 1/2" for example, or exceptionally long zones, the Astro should be sufficient.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream