Why is Home Depot the only option? I usually
shop on Craigslist when looking for radiation! ;-)
But there's always those
auction site possibilities too.
Panel radiators can be ordered online from
multiple vendors.
If you don't know how much heat the room needs, how do you know how much baseboard or other radiation it needs?
If that room is one of several on the zone, the radiation to room load balance has to be reasonably close to avoid over or under heating the room. Performing an
IBR or
Manual-J type heat load calculation on a room-by-room basis and comparing the ratio of room radiation to the room load for each room would give you at least a range. You don't want to freeze, but you also don't want to cook yourself out.
Most existing homes in NY could be heated with their existing radiation with 140F water, but not all boilers can operate there without short-cycling or running into condensation issues. That IS a separate discussion, but for now work on figuring out how much heat you need in that room relative to the others, and the proportion of "baseboard-equivalent" that would be to balance reasonably with other rooms on the zone. From that it's possible to spec a radiator that fits. If you're running 160F+ water there's no question but that there are radiators out there that will fill the bill that fit into a 24" width.
Kickboard heaters are noisy and create a wind-chill, and develop rattles, squeaks & buzz over time. It heats the room sure, but it also makes the people in the room less comfortable. If you can get there with radiators (not baseboard convectors) you maximize the comfort.