To heat a 10X10 wall tent with 3 foot side walls and a 6 foot peak. I am not really sure what size I need, but figured something used would suit me just fine if you need to clear some garage space out.

I don't have one for sale, but in case it's helpful, my tent is about the same size as yours and I have the medium Kni-co stove, which is 19x12x12 and it has worked well for me. One size smaller would probably be ok except in deepest cold.

Thanks Jay!