The outside of the boiler is just sheetmetal held together with screws. Once you remove the screws and the boiler jacket (outside of boiler), you will see the cast iron sections that the water passes through. There are 2 to 4 long bolts, probably at least 2' long, that hold these sections together. Chances are, the nuts will be rusted to the bolts, so forget about a wrench, just use a sawzall or a hacksaw to cut the bolts and remove them. After the bolts have been removed, you can use a crowbar and a large hammer to separate the boiler sections. This will make it much easier to remove from the house. By the way, being that cast iron boiler sections are flat, they make excellent weights for the beds of pickup trucks for better control when driving in snow. If you or a neighbor own a pickup truck, you might consider saving them for winter use rather than just scrapping them.