We are replacing our failing air conditioner and are considering heat pumps among the options. In heating mode, the heat pump would supplement our existing oil-fired boiler hydronic baseboard heat. I am confused about how thermostats would handle multiple sources of heat in a room, especially when they do not control all of the heat sources.
One of the thermostats seems straighforward: the one that controls the air coming from the compressor/air handler to ducts throughout the whole house (there is a single central air zone). It also controls one of the hydronic heating zones. It's easy for me to understand how this thermostat would be able to regulate heating from the heat pump and oil.
There are several other thermostats, however, that control only hydronic heat to their heating zones (via zone valve switches), despite the fact that these rooms also have vents from the ducts. How will these thermostats behave when heat is being supplied from both the heat pump and hydronic heat?
My guess would be that the thermostat that controls the central air will run the heat pump at a certain level, and then the rest of the heating zones' thermostats will just run the hydronic heat to close the gap between whatever central air they're getting and the set point. Is this fine in practice? Does it cause any problems with temperature swings?
Is it best practice to instead have the thermostats networked together or all wired to a zone panel or something rather than acting independently in this scenario? Our contractor has proposed only replacing the thermostat that controls the central air (since the heat pump is a variable-speed inverter).
