help with wiring wood boiler thermostat to run gas furnace forced air blower

It was the heat exchanger in the plenum, not the boiler. Jeez, and English is my native tongue....

I'm a bit lost here and probably not asking this correctly because I don't really understand the discussion so far. I'd like to use my oil furnace with a heat exchanger from a biomass boiler. I'd like the normal function of the oil furnace to be preserved in case I can't tend to the biomass. I'd like a circulator to come on, get hot water into the heat exchanger, and only then for the blower fan to come on, both in response to a T-stat. Isn't this best? How do I do it? Put me out of my misery here....

This depends on how the user sets it up. Most OWB's run a single circ pump that runs 24/7 and the house thermostat only controls when the fan comes on in the furnace. Many of us indoor burners, especially those of us with storage, will have a circ that sends water into our tanks when the boiler is running at proper temp but we'll also have a second circ pump that sends water to our heat exchanger/load when needed.

I personally control both the furnace fan and my second circ pump (for the heat exchanger) with a second thermostat and a relay. I only run water through the HX when there is a call for heat.

Run your circulator off the room thermostat and launch the furnace fan with a snap switch attached to the return line of the coil. That way you won't get a blast of cold air before the coil is up to temperature.