AC Sizing - Ductless Mini Split Upgrade

I have a 10x10 room with 4 Gavita DE 1000w HPS. I live in an area were it get pretty hot in the summer, many 100+ days, and nights can stay relatively warm.

I currently have a 14k portable single hose AC, and it does the job but just barely, and on warmer nights it can't quite keep up.

I'm looking to get one of those ductless mini split DIY units. But trying to decide if the 12k will be sufficient, or do I need the 18k?

Definitely go with the 18k. It's better to oversize than under size with a mini, they aren't just on or off like with a normal AC unit. So an over sized unit can run just as hard as it need to do the job.

If you will use it when it's cold outside make sure the unit has a low ambient rating that will suffice. Some Mitsubishi units I have seen will run to -28F.

Make sure the unit will auto restart after a power outage.

I'd get a 24k btu especially if gets that hot. 18k btu is only 4500 btu per light. For double ended 1k it's recommend to run 6k btu per fixture.

My last room was 4 gavitas and I cooled it with a Daikin 24k btu.