Boilers are really slick. I have a wood furnace for primary winter heat and keep thinking about trying to rig up a means to heat water for water changes, but haven't.
I don't see why the baseboard heat wouldn't work presuming it's enough wattage to heat the room well enough. I've considered some of the freestanding, rotating heaters, but haven't made a purchase yet. Currently I just have a handful of tanks with heaters, but not a heater in every tank. That combined with a dehumidifier has kept all the tanks warm enough.
All of my tanks below waste height have a heater and the biggest tanks above that do as well, but since warm air rises, the rest do not. The heated tanks are ~77-78F, while the rest are 74F-76F typically.