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Thread: Modulating V Non and Aluminum Heatx v Cast Iron

  1. #1
    DIY Junior Member srbell's Avatar
    Join Date
    Jul 2011

    Default Modulating V Non and Aluminum Heatx v Cast Iron

    1. Iím looking to replace my only natural gas boiler with something more efficient and have been in the process of getting bids. The house was built around 1905 and uses the old cast iron rads. Iíve been leaning towards a high efficiency (90%-97%) Weil-McLain. Iíve been going back and forth between the modulating and not. So my first question is that. What should be considering when choosing between modulating and non-modulating.

    2. Secondly, I had a contractor in today and recommended against any of the high efficiency boilers instead recommending that I go with something in the 80ís. Again he suggested Weil-McLain and then the Aruba 3 by Crown Boiler. Does anyone have experience with Crown?

    3. My third questions comes from his reason not to go high efficiency. He stated that since Iím running an old system that the rust from the water could gum up the aluminum heat exchanger so Iíd be better going with a cast iron heat exchanger. Has anyone every heard of this?


  2. #2
    DIY Member tk03's Avatar
    Join Date
    Jan 2011
    Harrisburg, pa


    As far as boiler operating efficiency the most efficient operation would be the modulating boiler. When the boiler is condensing you gain btu's from latent heat until the condensing mode is over. Now the efficiency drops quickly. Even though the efficiency drops it never drops below or in most cases as low as cast iron boilers. The most important thing to remember is proper sizing, installation and outdoor reset. Keep in mind that system efficiency is more important than boiler efficiency.
    Let's compare these things also. Life cycle costs which include, installation cost, operation costs, maintenance costs and service costs.
    When all things are compared there is not much difference between the two units over the life of the products. The cast iron boiler will last much longer but that may not be the best thing wither. I believe even though the boiler is still good 15 years from now, life expectancy of a mod/con boiler, you may still want to change out the cast iron boiler due to technological improvements.
    If I was going to install a cast iron boiler I would be looking at cast iron boilers that are capable of returning cooler return water temperatures. Most cast iron equipment the minimum return temperature should be a minimum of 130f. There are other cast iron boilers that can return 100 - 110f which will increase system efficiency.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    There are mod-cons that use SS heat exchangers verses the aluminum one in the Weil-McCain. I do not know how they've been working, but the earlier ones reportedly had some leaking problems. I ended up with a Buderus unit that has been working well for me, has a wide modulation range, and a SS boiler assembly.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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