I am just beginning to research this topic and find that there are many more options than I originally thought. So far one of my favorite products is the Envi wall mounted heater. It only weights 10lbs. And is run on the standard 120v.
I am continuing to read up on this unit and encourage you to... Knowledge is power right! Here is a link to their site http://www.eheat.com
If you prefer a wood burning stove I found a great option and the reviews are extremely positive! You can read more here: