Gas Hot Water Boiler or Gas Furnace?

Bake

Hello.  I have a 2 flat building that is about 60 years old...maybe a little older.  Each unit has 2 bedrooms, 1 bathroom, living room, dining room and  enclosed back porch.  Each unit is about 800 sq. ft.  The basement is finished...as I use it to stay overnight from taking long drives home.  The building currently has a hot water gas boiler with the older cast iron radiators.  I am looking to separate the heat and place that responsibility on the tenant.  I have been told that I can keep the current boiler for the first floor and install either another gas hot water boiler or a gas furnace for the second floor. 

If I choose to install a furnace on the 2nd floor, the only place to set it is on the enclosed back porch...which is insulated.  The contractor would have to get through the brick separating the porch and run the duct work over head.  Can the return be placed on the enclosed back porch or any area that is about 10 x 12?  Or does the return have to be in an open area? The porch has a door and on the other side of the furnace is a bedroom with a door.

If I choose to install the boiler, the contractor stated that he can do most of his work from the basement.  Therefore not making holes in the walls for the duct work and vents....less clean up and patching time. He stated that he would run new copper pipes to the 2nd floor.

Can you tell me:

which system is the better solution? which system would be the least expensive to install? which system provides the better heat? which system is more efficient regarding monthly expense?  Please provide me with pros and cons.

I thank you in advance

Tim McElwain

I believe others answered

you on the Wall section of this site.