I have an infrared space heater that I’ve had for close to 10 years now, it still works as well as the day I got it. They don’t make the model I have anymore, the only thing online I could find about it was from 2010 and it didn’t even have a picture. Here is something similar though. It’s going for like $80 on Amazon (I think I paid closer to $100 for mine).
I use the space heater for my bedroom specifically but,I like it because it is portable so I can bring it into any room easily (mine has wheels and is pretty lightweight). It’s also cool cause it doesn’t get hot so there’s no burn or fire risk.
I had one of those infrared box heater things (like this one). Kept my house to sweatshirt-level comfort when my central heat died one week. Area was bigger than your request, but also insulated living area.
I use two Lifesmart heaters. I also insulated the garage door and put a new weather stripe down.
LIFE SMART LifeSmart 6 Element... https://www.amazon.com/dp/B00F4BHC24?ref=ppx_pop_mob_ap_share