We're in a 3100 sf 2-story cape house (with attached garage underneath) in New England and will be remodeling/expanding part of the 2nd floor with higher rooflines, etc. As part of the remodel, we'll be adding a new heating & A/C for the remodeled portion of the 2nd floor. Our current setup is a gas furnace (forced hot air) in the basement with central A/C. We also have a snowmelt system for a 1300 sf driveway running off a 5-yr old Viessmann boiler (net 230-240 BTUs).

the new remodel would have closed cell insulation in the roof and walls, so the attic would be conditioned space. the new zone upstairs would be ~1000 square feet.

We have 3 heating options for the remodel and are at a loss:
a) gas furnace in the attic
b) hydro air off the Viessmann boiler with a flat plate heat exchanger, isolating the snowmelt antifreeze on its own loop. the boiler would run hot water to an attic air handler for hydro air
c) hydro air off the Viessmann boiler with an indirect water heater as a heat exchanger. in this scenario, the snowmelt and boiler would run antifreeze/glycol mix and there would be a separate loop to the water heater. the water heater would run hydronic water to an attic air handler for hydro air.

the 2 hydro air options would have the benefit of being able to run a small garage unit heater as well. however, they are substantially more ($5-10K) than the attic gas furnace.

Interested in thoughts on which to choose and why. Thanks!!!