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Mixing radiant floor and steel rad on the same boiler

PieCa Member Posts: 31
Hello there! First of, I know pretty much nothing about heating... So bear with my silly questions...

I have a McLain ECO 70 at home and some 70 year old cast iron rads. I wish to remove half of them (the ones on the main floor of my house) and install heated floor instead. I might also replace the cast iron rads with steel rads on the second floor.

Can that be all connected to the same boiler at the end? Or would that imply that I'll need to change the boiler or add another heating appliance? The boiler is quite new (from 2016) and that would be a pity if that investment (which was from the previous owner) was for nothing...


  • Zman
    Zman Member Posts: 7,355
    edited November 2019
    It can all be done with the boiler you have. You will need to find a competent designer/contractor to work out the math. You may need to add a mixing valve if the different zones require different water supply temps.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • PieCa
    PieCa Member Posts: 31
    Very interresting! Thanks!

    I think the current temp of the boiler for the cast iron rads is 145F. But I'll replace the cast iron with some steel rads on the second floor of the house and have heated floor on the main.
    Can stell rads and heated floor use the same temp?
  • psb75
    psb75 Member Posts: 571
    It's a shame that you are replacing the cast iron rads. They are excellent heaters.
    Steel panel rad. water temps. can match-up with radiant floor especially if the radiant floor is "underfloor tubing with aluminum plates and insulation. Not so well with radiant slab.
  • mattmia2
    mattmia2 Member Posts: 5,737
    Why do you want to replace the ci rads? the ci will be more even because the mass will retain and radiate heat a lot longer than the steel rads. if you get the anticipator on the t-stat dialed in right and maybe add some TRVs for balancing the ci will be a much better system
  • PieCa
    PieCa Member Posts: 31
    The ci I have are quite bulky. They were installed a while back ago (probably more than 60 years ago) when the windows were single glased and the wall not insulated. I guess I could replace them by smaller units too but I also really like the look and feel of the modern slick steel one.

    In the main floor they will have to go. I'm opening the space and changing the layout and rads on/next to the walls are an issue.

    If I were to keep the ci upstairs and have radiant floor on the main, would that be a mote challenging configuration?

    Also, I'm planning to use engineered bamboo floor on the main floor where the radiant floor will be installed. Is that an issue?

    Thank you all for your inputs!
  • hot_rod
    hot_rod Member Posts: 16,550
    Ideally a load calculation and system design would spell out what temperatures and gpm flowrate is required for the various emitters. Probably the radiators cast and steel could be on one temperature, outdoor rest controlled ideally.

    The floor will need to be supplied with a mixed down temperature. A 3 way thermostatic, properly piped, is a simple way to do a mix down.

    I think any of the engineered floors work best with radiant, bamboo over radiant has worked well for me. With any wood care taken to not over-heat it, or the subfloor. A design would spell out what temperature and if in fact the radiant can handle the load alone. In some cases radiant floors need some supplemental heat.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream