Based on many inputs a much better solution is the heat pump. Big thanks to Harper and manassehkatz for the help, both answers are great and very helpful.
Long story short, my dad rigged up a crude ~800 sq ft. greenhouse using some 8 mil greenhouse film, and with the weather dropping to about 10°F in a couple of days, I am now charged with somehow keeping our tropical plants alive, outside, through winter. I plan to install a space heater to keep the temperature to about 45°F.
The heater I am about to install is this 5000W unit, but for contingency, should I need to go bigger, let's assume I'll be installing a 7500W unit. At 240V that works out to 31-ish amps, ideally. So the plan is to install a new 240V 50A double pole breaker in the panel, runs wire to where I need the outlet to be, install a weatherproof outlet box, and make a cord from outlet to heater.
This conduit will run from the 200A breaker panel (based on the main breaker, so probably not accurate), into the wall, to the greenhouse, which is about 50ft down the same wall (The breaker panel and greenhouse are on different sides of the same wall). The outer wall is brick. There is no basement or crawlspace (I wished...).
My questions are:
- Does this have to be a GFCI circuit? Or is GFCI even an option?
- I planned to use 8/3 UF wire to be on the safe side, but can I just use normal indoor wire since most of it will be in the wall?
- Do I need any kind of conduit tubing for the wire inside the wall?
- Can I use the same 8/3 UF wire to make a cord (like this) from outlet to heater with some male connector? Is it better to buy one?
- The heater shows two live connection and a ground, so 3 wires total. Does that mean I could just ignore the neutral wire altogether?
- Do I have to worry about the total power of my breaker panel? I have a feeling the main breaker rating isn't what the house can provide.
Disclaimer: I did some indoor 120V wiring for outlets and lights/fan fixtures and replaced breakers and 240V dryers outlets, but this is on an entirely new level. As much as I wanted to learn to do it myself, please let me know if I am making some fatal mistakes and should just get an electrician.