Not too sure if the problem with my furnace is it being undersized or an issue with furnace. The furnace is a brand new Goodman GMS8 80% 60000 btu in a 926 bungalow 9ft walls, ceilings are insulated, walls are not insulated, and 4 inch rectangle high supply duct(house was build in 20s). The problem that i am finding is that it is producing luke warm air and the furnace continues to run and run. I tried to adjust blower speed but even with setting set on high it will not even heat above 50. The supply duct on top of the furnace seems to be warm but not hot. Any ideas on why the furnace is only producing luke warm air and not hot air? And will this furnace even be enough to satisfy this size house requirements? I know ive seen some newer construction houses larger with a 60k looking for some imput.