Central Boiler CLASSIC Owner's Manual page 17

An alternative method is to install a line voltage
thermostat to control the blower on the existing furnace. In
this installation, a 120-volt line is run from the thermostat
to the furnace where one wire is connected to the hot (line
feed) and the other wire to the furnace blower wire. A low
water temperature switch may be installed to shut off the
blower if the temperature of the water is too low. This switch
is connected in series to the wire coming from the thermostat
previously mentioned. This switch must be installed so that
it does not affect the existing system thermostat.
Section 3 - Furnace Installation
NOTE: If a low water temperature switch is not
installed, the fan will run continuously even when
the outdoor wood furnace is out of wood. Not
installing the switch is acceptable if it is desired
to keep the water in the furnace the same
temperature as the air temperature in the house
to prevent the water in the furnace from freezing.
Fig. 23
Section
3
17