Gas and Oil Home Heating Furnaces - Question about 2 stage variable speed furnace

If you have a two stage furnace and the output for example is 72,000 high and 48,000 low would the furnace automatically kick into high stage when the demand exceeds the low stage output? More specifically, if you were in low stage and the demand exceeded 48,000 BTU by 1000,2000, or 5000 BTUs will it kick all the way up to 72,000 output(high stage)? I don't know if it would make a difference or not but the furnace would have a variable speed blower. Thanks.

if it is on a 2 stage heat tstat, the second bulb would bring in high heat. if it is jumped at the board, i believe there is a time delay. not sure how the VS blower would affect this.

the switch between low and high output can be done as hvac4u says.....but in Carrier two speed furnaces it may also depend how th original installer set the little dip switches on its circuit board. they can be set to run off a two stage stat, or to run in high fire only or to follow the internal program that Carrier puts in which is that with a single stage thermostat on an initial call for heat ot will start in low, after 16 minutes (don't ask why 16, that's what it is) if the furnadce is still running it will kick up to high and run in high till satisfied. on the next call for heat it will start in high, and then if satisfies in less than 10 minutes it will start in low again the next time.........that's engineering for ya

Thanks. Those responses cleared it up.