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old cast iron mixed with new munchkin

ken_6 Member Posts: 33
apt blg scenario. owner wants hi eff.concerned about going
straight munchkin. would like to split btu.leave say half of existing cast iron capacity and front load with munchkin.
a. how to control (don,t want mixing or injection reset.just want plain non 140 degree limited reset based on condensing boiler)

would i have to be concerned about corroding the cast iron

how would you set up

john sawyer of htp say there was an article about this in pm


  • Mark Hunt
    Mark Hunt Member Posts: 4,909

    I would not worry myself over the deterioration of CI rads due to the higher O2 content in lower temp water. In fact, I have never had to replace a CI rad for such a problem.

    A neat thing about old CI rad systems is that, like it or not, they kinda' reset themselves.

    I would be more concerned with the corrosion of the cast boiler block with lower water temps. I have definately replaced old boilers for this reason.

    The Munchkin LOVES low water temps. We installed a unit for a slab RFH system and activated it in February. I tested the combustion efficiency at 96%. The boiler was condensing like crazy!!!!!! Even with the burner at high fire, it had a time getting to 112* due to the "frozen" slab.

    For the application that you have described the Munchkin would fit perfectly!!! And come October the new boards will be available that will allow DIRECT reset of the modulating gas valve.

    This BTU generator is really making a name for itself and we quote them to all of our wet heat customers.

    Try it, you'll LOVE it!!!!!

    Mark H

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
  • Boilerpro
    Boilerpro Member Posts: 410
    I baseload often

    Control: tekmar 262 with Minimum supply off and sensor on system supply.
    Connect both boilers together with common supply header and common return header and then connect this P/s to main system loop. Install check valves on boiler outlets. Size boiler pumps to the load they will be carrying... The cast iron boiler will probably need alot less gpm than its capacity dictates since it now only recieves part load. To provide return protection to the cast iron boiler, if load is small enough you could use a Esbe thermix valve 1 1/2 inch--CV =20.4. Or you can use variable speed innjection: tekmar361. Program it for setpoint control and set mix target at a temp higher than max system supply. Install this sensor on cast iron boiler return and set minimum return temp (120F to 140F). I just set up a 361 similiar to this to protect both the lead and lag cast iron boiler in a church while the 262 provides full reset and am installing another like this reight now. I try to figure out the real typical day heating load and size the lead boiler this way. Here in northern IL that is about 25F outdoors and since there is so much internal gain in apartment structures, you can probably figure no heat is needed down to about 55F. Your typical day load would be 30F times the heat loss per F degree. You'l end up with a lot smaller boiler than you'd think (probably 1/4 to a third total calculated heat load on a design day with no occupancy and no sunshine). Hope this gives you some ideas, that owner can look forward to a very big dop in fuel usage.

  • ken_6
    ken_6 Member Posts: 33

    dear boilerpro.
    thank you so much for your very full reply

    being that the cast portion of the boilerplant is old and existing.(and i'm cheap and lazy)(the owner is cheap to)
    i was thinking.if the iron boiler will only come on in more
    extreme weather (the munchs would handle it till then[no rotate-fixed lead])when the reset would call for temps above 140, couldn't we simplify things
  • ken_6
    ken_6 Member Posts: 33

    dear mark
    thanks for your reply. radiation is copper fin. question
    was concerning :condensing boiler can reset all the way as stage 1 but cast iron stage 2 can only tolerate down to 140

    have you thought of this scenario and what would be the simplest way to handle it
  • Boilerpro
    Boilerpro Member Posts: 410
    Cheap or less expensive, which one do you want?

    There are likely to be many other ways to do this than I have come up with, but doing it cheap almost always is the most expensive solution. The owner will probably pay higher fuel bills than necesary and have to replace that old boiler alot sooner.

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