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Adding zones to a newly converted gravity system

arborus14 Member Posts: 4
We have a three storey building with a gravity hot water system. Because of the location of the boiler room the basement cast iron radiators are mounted on the ceiling so the water can fall back to the boilers. Not an ideal heating location.

We are replacing the boilers, adding primary/secondary pumping (Grundfos Magna) with low loss header between - connecting to existing, now oversized piping. We would like to add Runtal RF3 radiators to the lower basement wall with a thermostatic control valve to provide some heating control to the basement occupants. The new rads would be tapped into the existing gravity (now pumped) system.

If the upper two storey rads will not receive new control valves will there be any flow through the new Runtall rads? I believe the pressure drop through the existing gravity system is negligible so the system water may want to go to the new Runtal rads even though the pressure drop through them and the valves is very low. I guess I am just wondering if anyone has experience adding rads to an existing pumped (previously gravity) system.

Can a contractor easily add thermostatic control valves to the existing 60 year old cast iron rads so the entire system is controlled the same way?


  • Paul48
    Paul48 Member Posts: 4,470
    I don't know how feasible it would be, but you would be better of zoning the basement seperately.