Speaking as someone who had a serious leg break in an accident 20 years ago, I was darned-lucky to live in a bungalow and have made very sure that our design enabled downstair living.
Very happy to be " defeatist, pessimistic and generally avoidable "
the end-point is adjustable, to set what depth the nail head stops at, but the power (the dose of gas) is fixed on the 350, not sure about the latest one.
Was this particular AroTHERM split or monobloc? Anything with an indoor Hydrobox is going to take more space, and some units may be less reliant on a buffer tank, depending on your particular system design, temperatures, and volume.