Outdoor boiler plumbing

This is the year that I'm building and installing the big outdoor boiler that has been on the drawing board for several years. I'm planting this about midway between the house and the fabrication shop. The pipe run to the house will be about 65' and I plan to tie this into the house's existing boiler system via a 50 plate stainless heat exchanger. The zone to the fab shop will also be about 65'. The fab shop is currently heated by an oil fired hot air furnace. I'm using all 1" bundled and insulated PEX tubing. My big question is about the fab shop. I have 2 options here. I'm keeping the oil furnace in place as back up.
Option 1 is to install a water to air heat exchanger such as a truck radiator on the cold air inlet to the furnace. This would be convinent to distribute air thru the existing system in the 2000 sq-ft shop. But as with forced hot air it would be on-off/hot-cold all the time.
Option 2 is to install along the wall facing the boiler, 2 iron radiators I already have (pictured). These are a 22 plate and a 32 plate. hot water would be circulated full time thru these and a thermostatically controlled fan could be used to boost air flow as needed. As my experience with radiators is the heat is constant and the enviroment quiet and comfortable. In the floor heat would have been the most desirable route but it was practically unheard of back when the floors of the shop were poured. Which option sound the most viable? By the predictions of where the price of oil is going to go, I think having heating options will be a good idea this year.

I would use a liquid/air exchanger as that would be more efficient at delivering heat faster to a cold room. I would use a seperate high CFM rated fan running at a slow speed as that would deliver a high air volume with less noise and felt cooling breeze.

A belt driven fan would be best as it has more options available than a fixed motor drive. If no static pressure(resistance to air flow) then a box fan could work well here. A evaporitive cooler blower would also work well. A used AC/HP blower is another option as well a source for a used liquid/air exchanger(evaporator).

I would use a digital T-stat with programable set points to control a TDR(time delay relay) that would delay fan on for 1min until a relay controled zone valve would open thus preheating the heat exchanger before the fan kicked on. Using this method would keep that blast of cold air from hitting you when the unit first started.

So a block digagram would look like this:
T-stat(on)---zone valve open---TDR 1min delay---Fan on.

A second thought too your underground piping would be to use a empty
3rd PEX pipe in close contact with your supply/return pipes. If the S/R pipes every frooze then turn on hot water to the 3rd pipe would quickly thaw out the S/R pipes. The 3rd pipe would set empty at all other times.

T_Bone

I currently heat my 4000 square foot shop with a coal stoker fired hot air furnace.

I am working on an outdoor coal boiler setup, and have collected 150' or so of used commercial baseboard (1-1/4 iron pipe core) and plan to use that. I also have a LARGE (forget the BTU's) hanging water-to-air heat exchanger that I plan to plumb in, for extreme cold temps, and quick recovery when the overhead door is opened in bitter weather. HOPEFULLY, it won't need to run (howl) most of the time.

I will also heat an old farmhouse (office) with the same outdoor boiler.