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What is the difference between cast iron vs. stainless steel for an electric boiler?

bobt14 | Posted in Mechanicals on

We are installing hydronic concrete slab heating. the slab has already been poured, i thiink the HVAC guy did not use O2-barrier PEX tubing. As i understand it, this means that a cast iron boiler cannot be used. true? how good are the stainless boilers vs cast iron (reliability), what are the pros and cons, which one would you use? Electro seems to come up in my searches, probably a mid-size 34k to 51k BTU/hr seems appropriate. i was surprised to see that they seem cheaper than the cast iron models… but i’m not really sure what features i should be comparing. any education here would be appreciated!


  1. davidmeiland | | #1

    Sounds like you are going electric, not gas. Thermolec makes electric boilers with stainless vessels. I would call and talk to the applications engineers at any company you are considering buying a boiler from. Tell them what you have and what you need.

  2. wjrobinson | | #2

    Bob, you are pointed in the right direction. No cast iron with the PEX you have. Copper and or stainless.

  3. bobt14 | | #3

    Thanks. Stainless it is. This might be a repeat of an attempted post
    1) Installer is giving us a choice of Electro or Thermolec - which one is better? warranty is better on the Electro. price difference is $330 more for the Electro, is it worth it?
    2) Installer says we will need to decide on one of 3 methods for a priming circuit. What do i need to know about this?
    3) One more point of our design is that 2/3 goes to slab, 1/3 to Rehau RauPanel under hardwood and tile (over a raised foundation). Installer says that the supply temp will be the same for both areas, if anything the RauPanel will need higher temps. This seems completely switched to me based on the relative thermal masses and aluminum thermal spreaders. I was thinking that the Raupanel side should need a lower temp and be faster responding. What would the set up be to manage for either situation?

  4. wjrobinson | | #4

    Bob, this is a great site for a bit of steering. Sounds like your are doing your own designing, If you are and have specs you want used then present them to who ever is doing the work and go for it. IF you need a complete design from others for a fee there are sources for that too. For DIY design I suggest you start using the manufacturers for proper spec sources not a chat site such as this.

  5. bobt14 | | #5

    Nope, not a DIY. i don't have near enough experience to do that, i am just an involved homeowner. i am looking for a sanity check and trying to understand the technology to help steer any choices before they become permanent. This site has already been a big help, as a result of input, i have already steered away from using 2 water heaters that the installer wanted to use, in favor of a boiler. Perhaps i am using the wrong terms, by "installer", i don't mean to imply that i am spec'ing and buying the equipment, then hiring someon to install. The HVAC company, hired by the builder, is doing it all, i am just trying to get a handle on it to see if i agree or need to modify. isn't that what this site can help with? provide other people's experiences with various approaches, or tell me if i'm right or smoking something? I still hope to get some feedback on my questions. thx.

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