Electrical – What’s the wattage of the heater

The controlled AC outlet you linked to in the comment above seems like overkill unless you were intending to run all of them from one thermostat. I'd actually recommend putting all of them on individual thermostats so you can keep them in 3 different heating zones. Not only would this be much cheaper (the relays don't even include the thermostat), but it would be a "plug and play" solution without having to wire all of the signal wires back to the relay. I'd take a look at something like these.

Well the fan is going to need 240 volts. If the existing wiring has not been wired for a 240 volt fan then it needs to be changed. This would involve opening the main breaker panel. I would recommend an experienced electrician for this. If it is already set up for 240 then that part is good.

The owner's manual for the fan should explain the wiring but my guess would be since the fan is rated for 240 or 208 then one of the wires labeled L1 (possibly the blue) would not be used for 240. The other black wire should be labeled L2. The two blacks would then be connected to the black and white of the cable, and the green is your ground wire that gets connected to the bare wire of the NM cable.

If this is your first project with electrical work I would recommend getting the assistance of an experienced electrician to guide you.

Good luck! 😊