We have a gas boiler and radiators for heat (original to the house), and forced air A/C retrofitted. The A/C is mounted in the attic above the 2nd floor and it took some closet space to run vents down to the 1st floor, but it works very well.

Is your priority for heat or A/C with the new system? Attic mounted A/C works well for cooling, but the heating unit may have trouble pushing heat down to where you want it. A basement mounted forced air heating unit with floor registers works better for heating.

I don't know what fuels you have available, but we also reduced fuel costs a lot by converting from oil to gas. We used a mid range Buderus gas boiler that is marketed as a "conversion" unit and it is much cheaper to run than what our neighbors pay for oil.

Bruce

Thanks for this. Once our oil furnace is ready to be replaced we will move to a propane one. Good point about pushing hot air down.

Yes, you could use an air handler. It is essentially a furnace without the burner. It has a hot water coil in it and you pump water from the boiler through the hot water coil and the blower will move the air. The unit should be provided with the correct cooling coil to match your current condensing unit. The boiler will continue to drive the radiators. ADP First Co and others make air handlers.

Thank you. We have to heat two stories. Is it better to do so from our basement Ac unit rather than the attic one?