is this how a residetial boiler with a fan works?...
There can be differences but with most hydro-air systems the stat calls for heat, the zone valve opens starting the circulator and boiler. The fan can start at the same time or it can be controlled by an aquastat on the return water line from the coil. When it gets hot it turns the fan on. This just keeps the fan from blowing cold air until the coil heats up.
also would there be a seperate coil in the duct for each zone and therefore a limit or temp sensor at each coil to start the fan?
There is a separate fan coil (air handler) unit for each zone with it's own associated ducting. Like I said, the fan can be started as soon as the stat calls for heat or they can use an aquastat on the water line.
I have seen systems that are further zoned with dampers in the ducts and a controller that interfaces the T stats and dampers then operates the zone valve as above.
Keep in mind also that each air handler usually has an air conditioning coil also so it is used for both heating and AC. This further complicates the fan control and the way it is wired to the T stat.
I should add that the T stat is wired to the air handler which in turn controls the zone valve and outdoor AC unit, except when additional dampers are used.
-Hal
[This message has been edited by hbiss (edited 12-03-2005).]
