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Replace H/W Radiator with Baseboard Heat Question

Tboans Member Posts: 5
I have a house that has a one pipe hot water system. I want to replace the Cast Iron radiators with baseboard heaters. Do I have to replace the feed and return pipes? How do I determine the length of baseboard that will be used? I have used the slantfin heat loss calculator, but the numbers look to be too low. They are saying to replace an 5 foot section of radiator with 8 feet of baseboard. If I were to "unlooop"the radiator, the tubing would extend about 30+ feet. I am not expecting to need 30 feet of baseboard, but I assumed it would need more than 8 feet.

I know my return lines will be in a different location, so will I have to move the return line connection to the main or can I just tie the PEX back into the return near the main? Whould I be better off changing this to a loop system?


  • A.J.
    A.J. Member Posts: 257
    Do not mix

    T do not mix cast iron and copper thin tube on the same zone hey have different cycle rates. The room with copper will always run colder!
  • Tboans
    Tboans Member Posts: 5

    I didn't know about the cycle rates. i know you shouldn't mix baseboard and radiators, but can i seperate them into seperate zones on the same furnace. If i keep the 2nd floor cast iron rads and make it a seperate zone, can I cap off the feeds/returns for the first floor and make it a baseboard loop? have the 2 returns meet right before the circulator pump and then have 2 zone valves. how will that work?
  • tim smith
    tim smith Member Posts: 2,752
    changing radiators

    If you want to make zones, you will have to repipe at the boiler to allow for boiler protections. ie primary/secondary piping. Then yes you could have one floor of cast iron and one of baseboard. PS Rather than baseboard fin tube, look at Runtal UF series steel rads. Quiter w/ better output in same dimension and also look quite a bit better. Closer to cast temps also than fin tube. Good luck, Tim
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