Helyn
Yes, we are only getting single phase, the largest single phase available was sufficient for our house which is not large and we do not have extremes of climate here.
If building new if you can get 3 phase if available in your area supply charge for meter is same price only extra is for additonal cable electrian has to run.
I had 3 phase installed for brivis 18 kw unit draws 8-9 amps per phase but when combined only 18 -20 amps single phase unit same size i fyou can get one would be 25-26 amps?