R290 is just propane, and it has a low Global Warming Potential. I see a lot of the new portable A/Cs use it. Apparently it's also more energy efficient. Obviou

R290 is just propane, and it has a low Global Warming Potential. I see a lot of the new portable A/Cs use it. Apparently it's also more energy efficient. Obvious downside is that it's flammable.