Someone offered me a four foot long under window cast iron radiator. Perfect for an under window spot in my office. But, I already have slant fin baseboard radiator in there. Someone told me that you can't mix the new and old stuff. Any thoughts on this?

Its not that you CANNOT mix these two types of radiation - the fact is you already are and you have first hand experience in seeing that the old system heats far better at lower temperatures than the new loop of expensive baseboard.

now that written -- if you were to place this fine old radiator in line with the baseboard already in place -- the base board would sort of simply become a conductor line - and not radiate much energy into the room as the radiator would give off so much more heat with the correct water temperatures to heat the rest of the house.

Do you see a down side???

hint -- not really - Whats the waste? - its free and the existing baseboard radiation is already there. You cannot look back on that.

So let me testify that I have a zone - my master bedroom - working almost the same way but instead of baseboard - I have modern pex and transfer plates under the wood floor - makes for nice warm feet in the morning - but the heat loss of the room is too great for that alone - so I have a cast radiator in the room also - and I built a custom bypassing control valve on it so when the weather is mild most of the energy is diverted away from it but when its darn cold --- it AND the floor are nice and warm.

This is why I tell folks the need to pay me to build temperature reducing loops for their old system zones and send boiler temp energy out to the baseboard. It usually doesn't happen - some lower bidder gets the job and then they whine about how the house is uncomfortable. Thermal reacting valves in old gravity conversions just don't flow enough to stay trouble free.

Just thoughts here

lets hear from others too!

Sting, you nailed it, nuff said.......