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Replacing old cast iron heat pipes in basement

demar Member Posts: 1
My 85 year old home originally had a steam boiler. The former owner in

the early 80s converted it to gas hot water. The original cast iron

radiators are in place, as are the original steam races that

circumnavigate the basement at a height just above my head.

I have a plan to have these pipes removed and replaced with PEX so that

they can be run through the joist bays and I can finish the basement.

At the same time I'd like to add a second zone for the 2nd and 3rd

floors (currently the entire house is on one thermostat). All the

first-floor radiators, and it seems, most if not all of the 2nd and 3rd

floor ones, have individual supply and return pipes to the basement. I

imagine for steam heat regulation this was a requirement, since there

are steam valves still in place on the radiators (most stuck wide open),

and no evident bypass lines/valves.

I've had a number of HVAC firms come in - some have refused, others have

sounded hesitant and bid accordingly, and one gentleman - a licensed

plumber and licensed HVAC guy, bonded and insured, is willing to go

forward with the work at what seems to be a reasonable price. He has a

design to use 1 1/4" copper mains and branch PEX off of them in order to

maintain circulation. I'm impressed with his knowledge and he has

done other work for me that I have been pleased with (mostly system


Without critiquing his design, I'm wondering if anyone out there has

done a similar project and can let me know about the potential pitfalls

of this "major surgery". How risky is this job? I would really like to

clean up the basement and have better temperature control upstairs

(we've already insulated and air-sealed btw) but would just like to know

what the risk of major trouble is if we embark on this project.




  • CMadatMe
    CMadatMe Member Posts: 3,086
    Done Plenty

    I take it the boiler is staying so I'll approach this as a cast iron boiler.

    Heat loss, heat loss, heat loss broke out per zone and measure the cast rads for their sqft of EDR. Then calculate my heating curve (my water temp starting point). Write it down you will not need 180 degree water. May only need one temp but never know that's why the breakout.

    Pipe the boiler primary secondary or hydro separator to protect it from cold return water temps. I'm a mixing valve guy so I would use a motorized mixing valve that can provided outdoor reset you could also do injection pumping. I use radiant style manifolds and homerun the rads with 1/2" pex. Dependent on budget would add thermostatic valves and let the system fly on outdoor reset using a Grundfoss Alpha or similar pump as my system pump. If no thermostatics and want zoning then zone the manifolds with full port zone valves while still using the Alpha or similar pump.

    There was an error rendering this rich post.

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