For a building with two boilers serving separate apartments, I'd like to simplify my design by having only one auto-fill and backflow preventer, and only one expansion tank.
These are combi boilers using a primary/secondary loop for each.
A single supply could fill both loops--it's all coming from the same cold water line anyway, right? The only risk would be mixing of loops under weird pressure conditions--should I use check valves? Is this common practice?