12ft ceiling “loft”, and yes, two separate spaces (rooms) within.
Even a relatively small (theoretical 8000BTU) 12SEER LG window AC can cool the space with air circulation between rooms but the heating is the more problematic factor. I’ve insulated as much as is practical in an all exposed brick 19thC building (my walls are lined with R7.5 Foamular and so on) but I still use around 4kW (for good number of hours) to keep the place warm. I am all electric out of necessity.
I’m “handy” so intend to do most of the install myself but keeping the warranties & codes intact involves a licensed HVAC/electrical installer to do the final hookup (vacuum pumping) … and in striking a deal it was determined I could get 2 for almost the price of one (installed) so I went with a “redundant” system.
My space will be more RAID 1 than RAID 0.