We are still in the planning stage A friend of The Other Half put in these folding doors/partition to their hall to have an airconditioned home theatre, and she wants to do something similar.Its not about it being practical or not, its whether u need it or not. U must think carefully lor.. If u dont need aircon in ur hall now and in the future, get a system 3. Don't install just for the sake of installing then never use, price difference quite a lot. Our ME system 3 (btu 9k*3) is $2850 and system 4 (btu 24k+9k*3) is $3850. Price difference of $1k! But if u might need aircon in ur hall in the near future, then might as well get a system 4 and have it done once and for all cos it's cheaper to install a system 4 compared to system 3 + system 1 (usually about $600-$700 incl labour fee). Most people go for system 3 + system 1 only because they frequently need to switch on all 4 fancoils at the same time.
Now, both Mitsubishi Electric system 3 and 4 is 2-ticks already.
Like I was saying, I'm new to this sort of thing ... my understanding of your reply is that, a System 4 cannot run all 4 units at the same time? Is that correct?