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Opossablethumb; Generally, a high efficient (90+) furnace will not perform any different temperature-wise than a mid efficient (80). The main difference is the high efficient will normmally consume LESS fuel.
When a T stat calls for heat, the burner will start, and when the air temperature in the unit gets to approx 120 the blower fan will also start. The burner will continue to run until the T stat is satisfied and shuts the burner off. The blower fan will continue to run until the air in the unit is cooled off to approx 95.
If any overheating of the furnace occurs during the burner cycle,(caused by restrictions, dirty filter,dirty ac coil,etc the High limit will shut the burner down (safety)
Some units have pre-set controls, some units have adjustable controls.
Generally a heat cycle goes like this; ,air temperature in the warm air plenum will be in the 125-150 range. The fan should kick in at approx 120 -125 and continue to run until all warm air is expelled from the unit, usually around 95.
A high limit will usually kick out at 180 or so ,depending on the unit,etc.
Any air temp less than, say 90 or so will feel cool at the supply registers.
If you have a probe type thermometer $ 10. check out the temps at the plenum with burner(and running for at least 5 min) on ,and at the closest and furthest supply register .
Post back with these results and we can advise you further.
Also, check to see if you have 'adjustable' fan/on/off and High limit controls. If they are not the adjustable type, record the printed settings on the control.
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