The advantage to a hot water coil instead of a hot air furnace are from domestic hot water requirements. Oil is an inexpensive way to heat water. This would work well in situations were there is only one flue in an existing home, and 2 appliances are using it. Also, old electric hot water heaters can be a burden to an electric bill. Using an indirect hot water heater or a hot water coil, one appliance can serve two functions.
Electrical savings are often the best reason to use oil to heat domestic hot water.
We use ADP air handlers with hot water coils and air conditioning option. These are compact units which can be installed vertical or horizontal.