I desperately need help trying to find a heat/cool solution for a small space. I have a stand-alone studio next to my house that is approx 160sf, brick contruction, located in Atlanta, GA. Currently it has no heating or cooling in it (just electricity and hot & cold water, and natural gas could be easily extended to it if that made sense to do). It has tons of cellulose insulation in the attic (about 2 feet deep) and fiberglass in the 2x4 walls and 2 normal-sized energy-efficient windows. Bascially, the heat/cool needs are very small (guessing 5-7k btu max). However, I'm having a difficult time trying to figure the best way to heat & cool the space. I have only 110 going to the building, so would like to stay with that (to go with 220 I would have to add a circuit and run about 120 feet of new wire). There is no ductwork and it is only one large room w/ a bathroom in the corner that isn't totally isolated from the rest of the space. I would only use this space occasionally as a work/hobby space, but could be any time of year. Summer temps in the 90's (and humid) and winter lows generally in the 30's and sometimes 20's.
So given that information, I'm just not sure what type of heating and cooling system I should use. I thought maybe a through-the-window heat pump, but most seem to be sized too large for the space and I've heard they don't heat well when temps fall below maybe 45 degrees or so, but I like the idea of the efficeincy if it would work OK. Another option is through-the-window AC with a heat strip, but because of the lower heating btu's on those units (and what I've heard about them) it seems that it might not heat sufficiently using 110 power (was looking at an LG 7k BTU A/C w/ 3850 heating btu heat strip). I've also considered through-the-window AC only, plus wired in base board units for heat, but not sure how many feet of heating I'd need. I've also heard of ceiling fans that have heat built into them, but not sure how much heat that offers or how efficient. And of course, a small mini-split is an option. I like that idea the most, except the cost seems to be quite high for those units (well over $1,000 plus installation).
Most of the time I wouldn't be heating/cooling this space to normal "comfort levels." I would mostly want to turn it on and make it comfortable when I plan on using it. However, I occasionally might want to let guests stay there when they visit, so would want them to be able to be comfortable too.
Is there anything that you could recommend that might best meet those needs? I know there is probably no perfect solution, but I'd like to keep the cost somewhat reasonable, while making sure comfort is possible when needed, which won't be that often in general. Any suggestions you could offer would be much appreciated.