> The jobs they were describing the limit switches as doing are done on
> mine by the thermostat... as in "delaying fan start until a settable
> period after ignition" and "continuing fan use until a period after
> flame off".
>
> Now, the digital one does it by time and not temperature but....
So in other words, your thermostat combines the functions of the fan
thermostat and the room thermostat in the older designs. The fan delays
still have to be set, but they are set by time in the room thermostat
rather than by temperature in the furnace. Yours may be as good (does it
compensate for whether the bonnet is still warm from the last time the
burner ran ?) but I can't see that it's enough better to warrant replacing
or re-engineering the furnace. (On my furnace, the fan control loop is
entirely contained within the furnace itself, so is not low voltage suitable
for control by an external thermostat.)
Randall
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