As others have said mixing units wont respond the same in overall
comfort, your cast iron will retain heat for maybe an hour while even
cast iron baseboard will be cooled of much earlier. This will lead to
that room getting cool even while others are holding and radiating heat.
Cast iron have alot of mass, water and release the heat slower.
I was looking at heating a room someone-a hack, removed the large 4
ft x5 ft x 14" cast rads and put in forced air water units for more
furniture room, they never maintained even temps even though the Btu
was there. When the boiler went off so did the heat but the cast iron
kept warming for an hour. We got in real pro who pointed this out and
indicated a separate zone with new piping, thermostat and pump would be
necessary for him to guarantee comfort for baseboard or just put in the
same cast iron as was in the rest of the house, we went with cast iron
since this guy was a real pro that guarnteed his work in writing and did
everyones work in the town. Yes we are happy, it works as originaly
I dought you will ever be happy as the retention and slow heat
release of large cast iron will not be the same as baseboard unless you
run a separate zone, meaning piping, pump, and thermostat for baseboard.
Sure you can match the Btu but it wont hold the heat and the room will
cool faster when the boiler is not running, unbalancing your home.
Cast iron radiators sell for alot used and give great heat.