One thing to think about - if you need to heat the room, will you also need to cool it during the summer?
If the answer is "Yes", you might consider one of the more expensive portable heat/AC units. They ain't cheap but they're effective & easy to incorporate. Figure around $600.
I've got an enclosed garage that's aprox. 12 x 18 that I keep temps about 70 degrees in with nothing but a small household electric space heater. I live in a mountainous region of the tri-state area of NC/TN/GA. Days with temps not getting above low-mid 30s. And some days not even that high, but mostly averaging somewhere around 40 or so.
The 220/240 watt baseboard heaters are fairly expensive to run. That's what's in my home, and rarely used. They're just not ver efficient. There's also on in my enclosed garage but the space heater heats the room much better, so I don't use the baseboard heater.
The more you put into insulating the room the more heating/cooling options you'll have. Lining a room the size of yours with Refletix can be costly but will save money in the long run and well worthwhile.
Have a good one!
HH
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Due to political correctness run amuck,
this ol' hillbilly is now referred to as an:
Appalachian American