The conceptual drawing below shows how easy to connect the outdoor boiler to any existing
boiler or hydronic heating system. (The plate exchangers and pumps need to be properly
sized to match your indoor heating loads and the required hydronic system the delta T)

There are many variations from the above described "typical heating systems",
the most common would be adding slab heat to your basement and garage concrete floors.

The conceptual drawing below depicts a
"Typical Indoor Pressurized Boiler Connection"
to an outdoor central heating system.