Gas furnace question

[dt67467]

The air from my gas furnace starts out hot and cools to nearly room temp as the unit runs. This causes it to run for hours with no progress in warming the room. If i shut it off for 10 - 15 minutes and turn it back on, it starts out hot again, but the end result is the same. Any help? Thanks

[4ftBanger]

Two things to check -

1st - Are the burners staying lit through the cycle. If they are not staying lit then you likely have an airflow condition causing a heat exchanger overheating situation or a faulty temperature limit switch.

2nd - Check your ductwork. Even a small leak in the return air ducting, especially in an unconditioned space like an attic, can cause the relative supply temperature to be a lot lower than normal.