You can cut a rectangular hole in your duct work and insert the heat exchanger. You need a blower to circulate air through your house. Usually there is an excising oil or gas furnace that as a blower in it.
My EFM 350 feeds a heat exchanger in my forced hot air system. It works very well. The boiler also feeds my kitchen zone (1 radiator and 1 kick space heater), and makes domestic hot water. It runs all year.