Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Adding radiant to cast iron hot water system

dmcsdmcs Member Posts: 19
Hi, Question for a family member who has a small 2 bedroom house with single zone hot water system with cast iron radiators. She is finishing off the top floor to be a master bed and bath suite, where she wants radiant heat.  They are using Quick-Trak.  When I added radiant zone to my single pipe steam system, I used a flat plate heat exchanger so as not to introduce water from the steam system into the radiant loop.  Is that a concern at all with adding radiant to existing cast iron hot water system? 


  • Paul PolletsPaul Pollets Member Posts: 3,360
    RFH for HW

    The radiant floor heating zone would use either a 3 way or 4 way mixing valve and pump for the new radiant zone. If there's a mod-con boiler, a 3 way valve is used. If a cast iron boiler, a 4 way motorized valve is used with a control (usually Tekmar) to prevent thermal shock of the cast iron boiler.
  • dmcsdmcs Member Posts: 19
    heat exchanger not required?

    Thank you for the response.  So there is no problem with running the same water that goes throuh cast iron hot water radiators through the pex for radiant system (with appropriate mixing valves of course to get the right temperature)?  For cast iron steam boilers I understood rust and debris in the pipes would cause problems in the pex and just wanted to make sure that issue is not present with hot water cast iron radiators. 
  • Paul PolletsPaul Pollets Member Posts: 3,360

    as long as you use barrier PEX piping, and the correct mixing valve/control, there will be no problems.
  • dmcsdmcs Member Posts: 19

    Ok, thank you.
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!