Welcome to ECN forums.
Additional information on the project is required;
Why are heaters required, other than freezing? What type/use group of structure/building?
Is the gen a legally required system, or is it an optional system?
Supervisory circuit to bldg mgt sounds like a good move. The FACP? Perhaps, if the water is destined for fire supression use.
More info will get you more answers and opinions.