HVAC solutions for 1300 sq ft addition
We just bought a house with an unfinished addition and are trying to figure out what the best HVAC solution will be.
The original house is approximately 1500 sq. ft. built in 1940. It has insulation in the ceiling (rockwool maybe?), no insulation in the floor, minimal insulation in the walls, and single pane windows (may be replaced in the future). Currently has an older split system which also may need replaced at some point in the future. It also has a chimney with an Ashley wood burning insert. We do have access to plentiful firewood.
The addition is two story, base floor approx. 1000 sq. ft. and upstairs is an"attic room", 4 ft. side walls approx. 300 sq. ft. Attic room currently has spray foam insulation on the ceiling, base floor has fiberglass bat in the walls, and insulation suspended within the floor joists. It will be connected to the original house through one hallway and the upstairs through a staircase w/closing door from base level. Base floor will contain large master bedroom, his/hers master closet, large master bath, laundry room, pantry, and half bath. Attic room will be used year round as upstairs "den".
Several concerns have been brought up; insulations differences btw new/old, costs of running multiple HVAC machines, and maintaining upstairs comfort year round.
We do have access to a cheap mini-split, would that type of system be appropriate for the upstairs? Will the base floor need separate systems for the new and old sections? Would having 3 "zones" save electricity since we often would only need to cool/heat one area (ie at night the master bedroom).
Ultimately we would like to heat and cool the entire space in the most efficient way, that will also provide reasonable comfort in all sections.