The most common way to build a zoned system is to use a separate piping circuit to and from each zoned area, equipped with either a circulator or a zone valve. Heat input is controlled by individual thermostats in each zone. Hot water flows through the zone circuit only when its thermostat is calling for heat. Although both circulators and zone valves have been used in thousands of systems, I prefer circulators. The cost is slightly higher, but so is the long-term reliability. If you install a multi-circulator system, be absolutely sure a "flow check," or spring-loaded check valve, is installed in each zone circuit to prevent off-cycle heat migration and reverse flow.

One piping alternative is called a "monoflo" system. With this approach, the baseboard in each room has its own thermostatic valve and can be separately controlled. The piping is arranged so that hot water is always flowing through the piping loop from which all the baseboards are "tapped." This creates a constantly...

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