I am in the planning stages of a total gut renovation of a four story row house / brownstone, roughly 4800sf (1200 per floor).

I plan to make the bottom floor a separate garden unit that will provide rental income. I will occupy the top three floors. I would like to have a heating / cooling system for the garden unit, another for the main floor, and a third for the top two floors.

My question is whether I should install traditional split HVAC units, small duct high velocity units, or a combination (for example, a traditional split system in the garden unit and high velocity units upstairs). Space for duct work is not an issue.

My contractor has suggested that a properly installed SDHV unit is better and more efficient than a traditional HVAC unit. Most of the reviews that I have read online suggest otherwise.

Thoughts?