I have two zones in my first floor forced hot water heating home. Each has a separate thermostat. There are no doors between zones and the air flow is unobstructed.

One of the zones (LR, DR) is hardly used. Hence, I want to keep the thermostat low.

The other zone (Kitchen, family Room) is inhabited constantly and set at 70 degrees during the day and 65 at night.

My question is: What thermostat setting should I use in the non-used zone? I am tempted to set it at 55 degrees but would that cause the other zone to work too hard to maintain temperature?