Switch to condensing- Question on one fan assisted radiator

My parents want me to switch them out from an old cast to a new combi. I'm not even sure they care about efficiency, they just want the room back the boiler and hot water tank are in as their house was built in 1827 and storage space is a premium.

In any case, my question is about one room which uses a mini forced air radiator. I'll have to take some measurements on it, but it is a metal box consisting of tube and fin which bend back and forth with a low velocity squirrel cage fan forcing air through it. The total length of tubing in this room/device is about 25% of other similar rooms, which I assume is why they had the forced fan.

I'm worried about the low output temperature of the condensing unit not heating this room. Do I need to treat this radiator any differently than the other baseboard units? Lower temperature = longer run periods, but if a radiator worked before regardless of type it should output the same btu as before? Or is there some drastic difference in btu output vs temperature curve on a fan forced radiator? If so, is it even possible the fan forced unit will be more efficient at lower temperatures than draft baseboard and heat MORE compared to the other rooms after the upgrade?

Thanks.