Actually the fire is never regulated by the Tstat, only the amount of time it burns at full blast. There are several adjustments on a stoker, the two main ones are:
1. the amount of coal that is fed into the fire, generally made by adjusting the stroke of the coal pusher
2. the amount of time the unit runs at idle (when the Tstat is not calling for heat), this setting is usually controlled by a timer which tells the stoker to push coal for a certain amount of minutes per cycle (which is usually a 1/2 hour or an hour)
When the Tstat calls for heat it tells the unit to run continuously at the stroke set in item 1 above.
When you set up the stove you adjust the stroke first to limit the amount of coal so as not to push burning coals off the grate, then you set the idle with the timers. Then when the Tstat calls for heat it runs the stove till the set point is met.
I know this may sound a little complicated but it isn't, it just involves a slight learning curve when you first get the stove.
As far as the burn rate, an 80 hour burn on a stoker is most certainly at idle (the lowest possible fire). Typical times for refill interval when it is cold out (colder than 20* F) is once per day (give or take based on about a million variables!
Hope this helps, welcome to the wonderful world of saving tons of money while keeping your house toasty warm!