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Copper fin boiler vs Cast iron boiler

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john123
john123 Member Posts: 83

I am considering a Lars mini-therm copper-fin mid efficiency boiler vs a Weil Maclain cast iron mid efficiency boiler. Would there be any advantages in the copper-fin boiler? (besides being a lot lighter and easier to lug into place). Would I still require a boiler protection loop—evidently the copper-fin heat exchanger heats up a lot faster than the CI boiler?

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  • Alan (California Radiant) Forbes
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    Both are great boilers. Yes, you still need low return water temperature protection. The Laars would be advantageous if you have non-barrier PEX.

    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
  • SuperTech
    SuperTech Member Posts: 2,200
    edited April 26
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    Proper sizing and quality of the installation is the biggest factor that affects reliability and efficiency. Both boilers would need protection from condensing. I lean more towards the Weil McLain than the Laars myself. I'd probably go with a cast iron Peerless over either of them, I see less problems with Peerless. But if you size your boiler based on an accurate heat loss calculation and install it according to the installation manual you should have a good results either way.

    Intplm.EBEBRATT-Ed
  • hot_rod
    hot_rod Member Posts: 22,348
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    I would be careful not to micro zone a copper tube boiler. The efficient copper and small water volume allow them to heat up very quickly. This can lead to inefficient short cycling, and shortened life


    Copper tube are great for pools and snowmelt applications. Consistent loads

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GroundUp
  • HomerJSmith
    HomerJSmith Member Posts: 2,477
    edited April 28
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    Just installed a LAARS JX 150. Mini-therm boiler have come a long way since the Lochinvar mini-therms. I'm impressed with the LAARS. If you are installing a boiler less than a 150, I would order a low loss header which is an add on. If you are connecting it to an indirect tank, the indirect tank control board is an extra and very expensive, but makes the connections very easy. I created a schematic for that control board that would allow the installer to mimic that board for less than 25 bucks.

    The drawback is that with an indirect tank the boiler has only one high temp setting which is for space heating. Whether that is a drawback depend upon what the boiler is heating baseboard or infloor tubing. If baseboard 180 degs is ok, no drawback, fast tank recovery.

    Based upon your conditions, proper installation and water quality is extremely important.

    The benefits are outdoor reset, economy mode, easy programing with a digital readout, LWCO, adaptable to side wall venting, , programmable delta-T, etc.

    The mini-fin that the LAARS replaced lasted 32 yrs and was originally improperly installed, but was updated with Caleffi manifolds and 172's and periodic maintenance. I expect the LAARS to last that long.

    All boilers will short cycle, especially so when the boiler reaches close to high limit. It is sustained short cycling over the whole heating curve that is undesirable.

  • john123
    john123 Member Posts: 83
    edited April 29
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    Thank you, thank you @HomerJSmith I too installed a copper fin boiler which lasted 35 years and am considering replacing it with another copper fin boiler (subject to comments that the CI boiler/mod con would be a better idea for this project.)

    Regarding the Mini Therm: How does the ODR work; does the boiler modulate at all? Can you use a 2 stage gas valve?

    Did you install a boiler protection loop? (or think you need to?—the boiler must heat up quickly?)

    Does it have an internal circulator pump? —- The diagrams in the brochure show the LLH right on top of the boiler.

  • hot_rod
    hot_rod Member Posts: 22,348
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    what type of heat emitters are you connecting it to?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • john123
    john123 Member Posts: 83
    edited April 29
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    @hot_rod Thanks for your interest. I am using (more or less standard) 4 and 5 tube cast iron rads.

  • HomerJSmith
    HomerJSmith Member Posts: 2,477
    edited April 29
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    If you have the LLH that is the protection loop. It has a boiler pump built in to the LLH. The sys pump turns on when the boiler RWT is above flue condensation.

    The ODR runs on a chart that is called a reset ratio that is programed by choosing a setting in the programing. It also works with the WWSD function. The ODR sensor (10K) is an extra cost.

    No, it is not a modulating boiler, nor does it have a two stage gas valve. But it does have an economy mode.

    Might be a good fit with cast rads.

    It is technologically a much better boiler than the ones that were made 35 yrs ago. I think that this boiler is more economical to run than a CI boiler.

  • HomerJSmith
    HomerJSmith Member Posts: 2,477
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    The LAARS is considerably less expensive than a Mod/Con. If your flue is 35 yrs old, you need to examine it to determine its serviceability. You can side wall vent with a Tjernlund vent. The boiler has the connections for that.

  • hot_rod
    hot_rod Member Posts: 22,348
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    The downside is no modulation or opportunity to condense. But a solid well traveled design in the copper fin boilers.

    it is getting tougher to find a basic boiler without any electronics or microprocessors involved.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Derheatmeister
    Derheatmeister Member Posts: 1,555
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    Alan FYI…. The Headers on the Copper tube Laars are made of Cast Iron which will corrode when subjected to non-Barrier /O2 rich systems 😕.

    HomerJSmith
  • HomerJSmith
    HomerJSmith Member Posts: 2,477
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    YES, the @Derheatmeister is right. LAARS sez that a flat plate heat exchanger is required between the boiler and the non barrier pex.

  • Alan (California Radiant) Forbes
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    @Derheatmeister @HomerJSmith Thanks, I didn't know that. I just see a lot of them on non-barrier jobs.

    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
  • hot_rod
    hot_rod Member Posts: 22,348
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    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream